Bénédicte Aldabe

Robert Anderson

Maija Lyly-Yrjänäinen

Agnès Parent-Thirion

Greet Vermeylen

Cecily Cecily Kelleher

Isabelle Niedhammer

Maija Lyly-Yrj

in the explanation of social inequalities in health in

Keywords: Adolescent, Adult, Europe, Female, Health Status Disparities, Health Surveys, Humans, Male, Middle Aged, Occupations, statistics & numerical data, Quality of Life, Regression Analysis, Self Report, Sex Distribution, Sex Factors, Social Class, Social Environment, Social Support, Socioeconomic Factors, Workplace, organization & administration, psychology, Young Adult

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Social inequalities in health have been described across a range of European countries for many health indicators, including [1 -13 ] self-reported health (SRH) which is considered as a powerful predictor of subsequent morbidity and mortality.

The association [START_REF] Idler | Self-rated health and mortality: a review of twenty-seven community studies[END_REF] between socioeconomic status (SES) and health is one of the most well-known findings in the epidemiological literature: the higher the social class, the lower the prevalence and/or incidence of health problems, illness, disease, and death.

Whilst many studies described social inequalities in health in Europe, studies trying to explain these inequalities are still lacking.

Identifying the factors that may contribute to these inequalities could be useful to reduce the prevalence of exposure to these factors, especially among the lowest social groups, and thus to reduce inequalities. Determinants of social inequalities in health are complex, and there are likely to be a number of important mediators, such as material, occupational, psychosocial, and behavioural factors.

Various theories have been developed to explain the pathways and mechanisms underlying these inequalities.

These theories [15 -17 ] include the materialist explanation, that put the emphasis on material conditions (i.e. access to goods and services, and exposures to material risk factors in the living and working environment), the psychosocial explanation, that focuses on psychosocial and stress related influences with a plethora of risk factors such as those related to social support or sense of control, and the behavioural explanation, that emphasizes the importance of behavioural risk factors in explaining social inequalities in health. The relative contribution of these factors has been very rarely explored to date at national level. Furthermore, very few studies explored occupational factors, that include [18 -20 ] specific material and psychosocial factors of the work environment, among other mediators. As explanatory or mediating factors probably are interrelated, some authors have suggested a simplified causal model to disentangle the direct (independent) effect of mediating factors, and their indirect effect through other factors.

;

According to this explanatory model, material factors might affect health [18 19 ] inequalities directly or indirectly through psychosocial and behavioural factors, and psychosocial factors might work directly or indirectly through behavioural factors.

To our knowledge, no study has attempted to explain social inequalities in health using harmonised data for Europe as a whole. Most previous studies were based on national or selected samples, and explored only a limited number of mediators that may contribute to these inequalities.

In addition, some studies describing social inequalities in health in Europe were based on surveys pooling data from [19 -40 ] several surveys/countries, making comparisons between European countries and generalizations for the whole of Europe difficult. ; ; [2 7 11 Mackenbach, in fact, underlined a serious lack of internationally comparable data on the topic of social inequalities in health.

] [START_REF] Mackenbach | Health inequalities: Europe in profile[END_REF] Our study aimed at providing an original overview of social inequalities in health in Europe, and at determining mediating factors for these inequalities. Thus, the objectives of the present study were to analyse the associations between SES, measured using occupation, and health, measured using SRH, and to examine the contribution of various material, occupational, and psychosocial factors to social inequalities in health in the working population of Europe.

Methods

This study was based on the data of the European Quality of Life Survey (EQLS), carried out by the European Foundation for the Improvement of Living and Working Conditions in 2003. Data were collected through face-to-face interviews in the respondent s home.

'

The basic sampling design used in all countries was a multi-stage, random one. Overall, more than 26000 interviews took place, [START_REF]First European Quality of Life Survey: Methodological review[END_REF] covering 28 countries in Europe (see ). Total response rate was 58.4 (range: 30.3 91.2 across countries, see ). For Appendix

% - %
Table 2 the purpose of this study, people who were not working at the time of the survey were excluded in order to concentrate on the role of occupational factors. Our final study sample included 12421 workers (6038 men and 6383 women).

SRH was the health indicator studied and was assessed using the following question: In general, would you say your health is and

" …"
response categories were excellent , very good , good , fair , and poor . The variable was dichotomised as good health versus poor " " " " " " " " " " " " " "

health ( fair and poor ).

" " " "

Occupation was used as an indicator of SES. Occupational groups were constructed according to the International Standard Classification of Occupations (ISCO-2008). Educational level was also used as an additional SES marker.

Results

The description of the sample is presented in . Many variables were significantly associated with gender, and almost all Table 1 variables were also associated with SRH. Only household tenure, work contract, and additional paid job were not associated with SRH. Significant differences were found for SRH and occupation between countries (

). The highest prevalences of poor health were Table 2 observed in eartern countries, and the proportion of manual workers was the highest in these countries, and the lowest in the scandinavian countries.

The association between occupation and SRH was significant for both genders, manual workers being at higher risk of poor health ( ). In each country, after adjustment for sex and age (

), the OR of poor health for manual workers was higher than 1 in most Table 1 Table 2 cases although not significant for all countries.

All potential mediating factors were associated with occupation, except commuting time for men and marital status among women (

). Strong social gradients were found for many of them, manual workers being more likely to be exposed to housing problems, Table 3 overcrowding, material deprivation, financial problems, low quality of public services, low access of medical services, temporary contract, dangerous working conditions, job insecurity, low decision latitude, low reward, low social support and network, low social participation, low level of trust, and social exclusion. The factors that displayed inverse social gradients (managers/professionals were more likely to be exposed to long working hours, high psychological demands, responsability for others, and additional paid job), or no clear social gradient were excluded from the analysis. The final selection of potential mediators is presented in . Table 4 presents the changes in ORs for manual workers after inclusion of potential mediating factors in model 1. Among material Table 4 factors, deprivation, financial problems, and housing conditions contributed to the decrease of social differences for both genders. Quality of public services for men, and access to medical services for women were found to be specific contributors for each sex. Taking these factors into account led to a reduction of the associations between occupation and SRH by 76 and 59 for men and women respectively.

% %

Among occupational factors, the biggest contributions to a reduction of social differences were found for reward and dangerous working conditions, and to a lesser extent for economic activity and decision latitude for both genders, as well as job insecurity for women only.

Taking these factors into account led to a reduction of the associations between occupation and SRH by 52 and 35 for men and women % %

respectively. Among psychosocial factors, social exclusion and social support contributed to explain social differences in SRH for men and women. Trust level contributed to explain social differences for men only. Taking these factors into account led to a reduction of the associations between occupation and SRH by 46 and 44 for men and women respectively.

% %

The ORs were further reduced when adjusted for combinations of two groups of factors ( ), the biggest reductions being Table 4 observed for the combination of material and occupational factors (91 and 73 for men and women). The independent contribution of ( 100 91) and 5 ( 78 73) for men and women.

% = - % = -
Finally, the inclusion of the material, occupational, and psychosocial factors together in model 1 reduced further the ORs by 100 in % men and by 78 in women, meaning that all groups of mediators independently contributed to the explanation of social inequalities in % SRH. Final ORs were consequently no longer significant.

Additional analyses were performed using educational level as a SES marker. The results were essentially the same, initial ORs of 2.10 (95 CI: 1.65 2.66) and 2.01 (95 CI: 1.61 2.52) for poor health were observed for the less educated men and women (model 1),

% - % -
and the main mediating variables were the same. Only access to medical services was found as an additional mediator for men. Material and psychosocial factors contributed to social inequalities to the same magnitude: 75 and 60 for material factors, and 45 and 54 for

% % % %
psychosocial factors, for respectively men and women. Two occupational factors were not found as mediators: economic sector for both genders and decision latitude for men. The contribution of occupational factors was found to be lower using education as a SES marker: 36 and 22 for men and women.

% %

Discussion

Social inequalities in SRH were observed, with ORs of around 2 for manual workers. Material, occupational, and psychosocial factors contributed to an explanation of these inequalities, and the four biggest contributions were found for material deprivation, social exclusion, financial problems, and reward at work. Material as well as occupational factors played a major role in explaining social inequalities in health. All mediators taken into account together explained social differences in health by 78 100 for men and women, the final ORs -% being no longer significant for manual workers for both genders.

Comparison with literature

Poor health was more likely to be reported among manual workers than among workers in higher occupational groups. This inverse relationship between SES and SRH is well documented in the literature, which consistently shows a higher level of poor health for people with a lower educational level, occupational category, or income. ; ;

The result from the EQLS data covering 28 countries in [10 24 39 ] Europe is in keeping with a previous study investigating educational inequalities in health in 22 European countries and showing ORs of 1.65 and 1.81 for the lowest educated men and women respectively. [START_REF] Dem Knesebeck | Education and health in 22 European countries[END_REF] Significant differences in SRH were observed between countries. Our study showed that the prevalence of poor health was higher in the eastern countries compared to others for both genders, as other studies had already demonstrated for both morbidity and mortality. ;

;

A differential reporting of SRH across countries may also be suspected due to cultural differences for example. Occupational 43 44 ] differences in health were found in almost all countries. Differences between genders were observed for SES, SRH, and mediating factors, and this reinforces the relevance of studying each gender separately. In terms of social inequalities in health, no difference was found between genders, the magnitude of these inequalities being similar for men and women. Some previous studies have reported however that social differences in health were more pronounced in men than in women.

;

Our study also showed that gender-specific factors may play a role in explaining social inequalities in health, [ 24 37 ] such as trust level and quality of public services among men, and access to medical services among women.

In this study, strong social gradients were found for almost all mediating factors. This is in agreement with previous studies showing that low SES groups are more likely to be exposed, for example, to high material deprivation, low decision latitude, or high job insecurity than higher SES groups. Some exceptions may be worth noting such as the occupational factors of psychological demands, [22 -24 ] working hours, and responsibility for others. Other studies have underlined the inverse social gradient for psychological demands.

; ; In our study, material factors were the set of mediators that contributed the most to reduce social inequalities in health, confirming previous results at national levels.

[
; Material deprivation played the biggest role in the explanation of these inequalities for both [18 19 ] genders, and this result was consistent with existing literature.

Financial problems also accounted for a substantial part of the observed [START_REF] Sacker | Dimensions of social inequality in the health of women in England: occupational, material and behavioural pathways[END_REF] differences, as previously reported by other authors studying educational differences in mortality in the Netherlands. ; Housing [ 19 36 ] conditions, quality of public services (men only), and access to medical services (women only) were also found to contribute to occupational differences in health in our study.

Occupational factors contributed to the social differences in health for men and women substantially. Important mediators were reward, dangerous working conditions, and economic activity -that may be an indirect marker of working conditions or occupational exposures-, and also decision latitude and job insecurity (women only). Previous studies have demonstrated the contribution of occupational factors, especially decision latitude and various markers of ergonomic/physical/chemical exposures, in the association between social class and health.

; ; ; Studies reported that 50 74 of occupational differences in health for men and 38 51 [24 31 -33 35 38 ] -% for women were explained by these factors. ; Job insecurity was reported as a mediator of social inequalities in self-reported

% [ 32 35
] health in a previous study in Spain.

In the present study, reward was also found as a mediator for social inequalities in health, [START_REF] Borrell | Social class and self-reported health status among men and women: what is the role of work organisation, household material standards and household labour?[END_REF] something never reported before.

Psychosocial factors also contributed to reduce social inequalities in health although to a lesser magnitude than the two other sets of mediators. Social exclusion was the factor which contributed the most to the reduction of inequalities, a finding never reported before. Our results were in agreement with studies showing the contribution of social support to social inequalities in health. Our findings suggest [START_REF] Sekine | Socioeconomic inequalities in physical and mental functioning of Japanese civil servants: explanations from work and family characteristics[END_REF] that trust level may be an additional mediator in social inequalities in health.

The retained mediating factors in our final models were able to explain social differences in SRH by 100 in men and by 78 for

% %
women, the final ORs being finally non significant. A previous study exploring simultaneously physiological, biological, and [START_REF] Arendt | Do risk factors explain more of the social gradient in self-reported health when adjusting for baseline health?[END_REF] behavioural factors observed a reduction of the educational differences in SRH by 40 in a population of Danish employees. The % contribution of material, psychosocial, and behavioural factors was also explored in a recent study from South Korea, tending to explain 56.5 77.5 of occupational inequalities in all-cause mortality, for men and women together. Material, psychosocial, behavioural, and -% [START_REF] Khang | The contribution of material, psychosocial, and behavioral factors in explaining educational and occupational mortality inequalities in a nationally representative sample of South Koreans: Relative and absolute perspectives[END_REF] biomedical factors contributed to reduce social inequalities in mortality by 73 83 in a Norwegian sample.

Social inequalities in

-% [START_REF] Skalicka | Material, psychosocial, behavioural and biomedical factors in the explanation of relative socio-economic inequalities in mortality: evidence from the HUNT study[END_REF] mortality were explained by 100 by material, psychosocial, and behavioural factors in the Netherlands.

% [19 ]

Limitations and strengths

The response rate (58.4 ) in the 2003 EQLS may be considered as low, and differed across countries. Consequently, it may be % [START_REF]First European Quality of Life Survey: Methodological review[END_REF] difficult to evaluate the impact on the results. However, previous studies reported that non-participants may be more likely to belong to low social groups, to have poor health behaviours and health outcomes, and such a bias may lead to underestimate the prevalence of [START_REF] Goldberg | Socioeconomic, demographic, occupational, and health factors associated with participation in a long-term epidemiologic survey: a prospective study of the French GAZEL cohort and its target population[END_REF] health outcomes as well as the association between SES and health outcomes. This cross-sectional study was necessarily restricted to working men and women. A selection bias may have occurred, i.e. workers in poor health may have changed or left their job and/or healthier workers may be more likely to work in more difficult jobs. Thus, the associations between work factors and health outcome may be underestimated as well as the contribution of these factors to social inequalities in health. The relative importance of material and psychosocial mediators might be different if the population studied was the whole population, and not only the working population. This study did not take into account lifetime exposure to the different mediating factors. This may lead to an underestimated contribution of the mediating factors to social inequalities in health. Some mediating factors may have been neglected in this study; this may be especially [START_REF] Monden | Current and lifetime exposure to working conditions. Do they explain educational differences in subjective health?[END_REF] the case for behavioural factors (e.g. smoking, alcohol consumption, physical activity) which may play a role in the explanation of social inequalities in health. ; However, behavioural factors may also be consequences of material, occupational, and psychosocial [23 30 ] mediators, and consequently their independent effects may be low, as underlined by others previously.

All variables studied were [START_REF] Van Oort | Material, psychosocial, and behavioural factors in the explanation of educational inequalities in mortality in The Netherlands[END_REF] based on self-reports. The use of SRH might introduce a reporting bias in our study, but a previous paper showed that measurement [START_REF] Crossley | The reliability of self-assessed health status[END_REF] errors were limited and SRH may have many advantages as a summary health measure. Furthermore, authors have reported that the use of SRH may lead to underestimate social inequalities in health, and not the reverse. [START_REF] Delpierre | Using self-rated health for analysing social inequalities in health: a risk for underestimating the gap between socioeconomic groups?[END_REF] The use of a large scale and comparable data across Europe allowed us to study each gender separately and to avoid problems of data comparability between countries. ; An additional advantage of this study was to be based on face-to-face interviews. Our study was [2 7 ] also able to determine the specific mediators of social inequalities for each gender. Our study aimed at describing social inequalities in health and also at determining mediating factors of these inequalities. For this purpose, three different sets of mediating factors were studied, each containing various variables. The relative contributions of material and psychosocial mediators were confirmed in additional analyses using education as a SES marker. However, these analyses were less powerful to identify occupational mediators, maybe because education is a more general SES marker than occupation.

Conclusion

Overall, this study sheds some light on the factors that may mediate social inequalities in health among working men and women in Europe. It emphasises the disadvantages experienced by manual workers and some categories of service workers. This study also underlines the need to address material deprivation, financial problems, social exclusion, -in other words all dimensions of poverty and deprivation-, as well as poor working conditions, to reduce social inequalities in health. More studies are needed to evaluate prospectively the role of a large variety of mediators in these inequalities, to better understand the underlying mechanisms linking these mediators to social inequalities in health, especially as regards specific indicators of morbidity and mortality. Finally, as the mediators and their relative contributions may differ between European countries, forthcoming studies should also focus on contextual factors that may contribute to a better understanding of social inequalities in health in Europe.

What is already known on this subject

There are social inequalities in health in various European countries Explanations for social inequalities in health have been reported but studies exploring a large range of mediating factors are still lacking.

Explanatory studies using European harmonised data are also missing.

What this study adds

Social inequalities in self-reported health have been found for both men and women across Europe.

Selections of mediators covering material, occupational, and psychosocial aspects were able to explain these inequalities by 100 and % 78 respectively for men and women.

%

The strongest mediators were those related to material deprivation, financial problems, social exclusion, and various working conditions underlying the importance of material and occupational factors. Some specific mediators were found according to gender.

Preventive actions focusing on these mediators may contribute to reduce social inequalities in health.

Appendix Countries and codes in EQLS 2003

  in relation to occupational factors was 39 ( 91 52) and 38 ( 73 35) for men and women, and was higher than the % = -% =independent contribution of occupational factors in relation to material factors: 15 ( 91 76) and 14 ( 73 59) for men and women. The % = -% =final contribution of psychosocial factors in relation to both material and occupational factors was lower, as their independent effect was 9

  The associations between SES and SRH, between SES and mediating factors, and between mediating factors and SRH were studied using Chi-square test. The associations between SES and SRH were also tested for each country separately, using logistic regression analysis after adjustment for sex and age, SRH being the dependent variable. Managers/professionals were used as the reference group.

	family/friends/neighbours, 4 items), social participation (voluntary work, political activities, and religious services, 5 items), trust level
	(towards people in general, state pension and social benefit systems, 3 items), and social exclusion (feelings of inferiority or uselessness,
	and lack of recognition or acceptance, 5 items).
	The associations between SES and SRH in the whole sample were then explored after adjustment for age (model 1) using multilevel
	logistic regression analysis with the 12421 participants clustered within 28 countries. The potential mediating factors, that displayed social
	gradients and were associated with SRH, were first introduced separately to model 1. The contribution of each factor (or a set of factors) to
	the explanation of the social differences in SRH was estimated by the change in OR after inclusion of the variable(s) in the model,
	according to the formula: (OR	model 1 -	OR	extended model	)/(OR	model 1 -	1).	[42 ]	Positive values indicated OR reductions and negative %	%
	values indicated OR increases. Only factors reducing social inequalities by more than 5 were retained in subsequent models. %	[32 ]	These
	models were adjusted for combinations of two groups of factors, and finally adjusted for all factors simultaneously, allowing us to
	calculate independent and indirect contributions of mediators. Indirect contributions can be interpretated as the contribution of a group of
	factors (for example material) through another group (for example psychosocial). Such a method has already been presented and used by
	others.	; [18 19 ]	Analyses were carried out using SAS and performed for men and women separately.
	Occupational factors included: sector of economy (coded using NACE classification), permanency of work contract, number of hours
	normally worked per week (including any paid or unpaid overtime), daily commuting time, dangerous/unhealthy working conditions, job
	insecurity (fear of job loss in the next 6 months), psychological demands (demanding/stressful work, and tight deadlines, 2 items), decision
	latitude (extent of influence at work and interesting job, 2 items), reward (salary and job prospects, 2 items), responsibility for supervising
	the work of others, and additional paid job.
	Psychosocial factors included: marital status, number of children, unpaid work (housework, care for children and/or elderly/disabled
	relatives, 3 items), work-life imbalance (difficulties to fulfill work and family responsibilities, 3 items), social support (help from
	family/friends/others in case of illness, advice, financial problems, or feeling low, 4 items), social network (frequency of contacts with

Three sets of potential mediating conditions were explored: material, occupational, and psychosocial factors. As we had a specific interest in occupational factors, they were distinguished from the other factors.

Material factors included: household tenure, housing conditions (shortage of space, rot in windows/doors/floors, damp/leaks, and lack of indoor flushing toilet, 4 items), crowding (number of persons per room), material deprivation (not able to afford at least one of these amenities or activities: car, home computer, washing machine, heating, holiday, furniture, meat/fish, clothes, and drinks/meals with friends/family, 9 items), financial problems (payment of bills, food, and/or rent, 4 items), neighbourhood conditions (noise, air pollution, lack of recreational/green areas, water quality, and area safety at night, 5 items), quality of public services (health services, education system, public transport, social services, and state pension system, 5 items) and problems with access to medical services (distance to medical centre, delay in getting appointment, waiting time to see the doctor, and cost of seeing the doctor, 4 items).

Table 1

 1 Competing interests: None. Licence for Publication statement The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all " authors, an exclusive licence (or non exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd to permit this article (if accepted) to be published in JECH and any other BMJPGL products and sublicences such use and exploit all subsidiary rights, as set out in our licence (). http://jech.bmj.com/site/about/licence.pdf " Prevalence of self-reported health according to age, occupation, and mediating factors Q4: quartiles of scores in the whole sample Other variables (household tenure, work contrct, and additional paid job) were not significantly associated with self-reported health

	-

Table 2

 2 Differences in response rate, self-reported health, occupation, and association between occupation and self-reported health between countries

	Country	AT BE BG

CY CZ DK EE FI FR DE GR HU IE IT LV LT LU MT NL PL PT RO SK SI ES SE TR GB p

  Managers, professionals 11.6 7.0 8.4 9.0 8.9 7.8 18.1 7.0 10.1 11.9 4.9 16.8 10.9 13.2 16.9 20.2 6.5 10.0 4.9 7.2 3.8 19.1 10.4 16.3 10.6 7.1 12.9 10.1 Technicians and associate professionals 20.1 50.2 34.7 44.9 18.9 21.1 24.2 26.8 35.3 22.9 36.8 19.4 28.6 39.8 30.5 27.0 24.6 34.2 19.3 29.3 23.1 20.6 24.6 22.4 33.5 43.7 44.3 30.7 Clerical support workers 23.1 12.1 8.8 0.6 19.3 18.4 5.5 23.7 14.0 26.2 15.1 15.7 14.5 24.1 11.0 7.3 26.1 31.7 24.2 18.6 12.8 12.9 19.7 19.7 12.8 10.9 14.3 16.8

	( ) Response rate %	63.9 70.4 81.0 82.4 75.1 52.4 68.8 91.2 83.4 91.2 39.6 75.1 32.5 63.1 72.8 64.1 66.1 91.0 62.0 66.4 59.8 55.7 51.0 61.6 30.3 53.6 37.0 79.2
	MEN
	( ) Poor self-reported health %	13.8 14.8 18.3 2.4 18.0 8.5 44.5 22.2 13.1 22.6 7.4 26.9 6.7 5.2 42.8 42.5 18.4 11.1 23.1 30.7 30.4 27.5 10.5 22.8 13.6 18.6 18.6 16.0 ****
	( ) Occupation %	****
	Managers, professionals	13.5 7.5 5.3 12.2 8.6 11.3 16.0 9.4 11.6 12.2 7.8 6.0 6.3 18.2 10.9 11.0 14.9 10.8 4.5 6.4 3.7 12.2 7.3 7.4 11.4 17.0 5.4 16.7
	Technicians and associate professionals	38.3 46.5 30.3 42.1 29.8 27.6 29.4 33.7 36.0 34.8 41.2 23.6 30.5 38.7 24.0 24.7 30.5 39.7 33.5 24.8 29.4 25.9 28.9 26.2 31.4 33.2 38.4 36.8
	Clerical support workers	8.5 5.8 0.8 1.2 4.9 9.6 0.0 7.9 6.0 6.4 8.3 2.8 3.4 12.5 1.1 0.9 16.1 16.7 16.6 3.5 7.3 2.1 7.3 12.1 6.4 3.2 3.5 7.5
	Service and sales workers	11.7 12.8 14.4 20.1 19.6 15.1 16.8 21.8 15.4 7.8 14.6 16.5 7.4 15.7 21.7 16.4 10.9 13.2 18.1 5.9 16.1 20.6 17.9 12.1 16.5 21.9 12.8 5.8
	Manual workers	28.0 27.4 49.2 24.4 37.1 36.4 37.8 27.2 31.1 38.7 28.1 51.1 52.4 14.9 42.3 47.0 27.6 19.6 27.2 59.4 43.6 39.2 38.6 42.3 34.3 24.7 39.9 33.3
	WOMEN
	( ) Poor self-reported health %	16.2 16.6 28.6 1.8 19.6 13.5 44.1 21.6 18.0 17.3 10.3 28.5 7.3 6.4 55.7 58.1 20.3 24.6 22.3 29.4 40.6 40.4 10.8 25.8 14.9 20.9 27.1 13.4 ****
	( ) Occupation %	****
	Service and sales workers	25.8 14.4 9.6 29.9 24.8 34.0 24.2 34.5 28.4 29.4 15.7 13.4 16.1 9.8 15.1 16.1 13.8 16.7 38.5 4.8 11.5 17.5 21.4 10.9 11.7 27.0 2.9 13.9
	Manual workers	19.4 16.3 38.6 15.6 28.2 18.8 28.0 8.0 12.1 9.6 27.6 34.7 29.8 13.2 26.5 29.4 29.0 7.5 13.1 40.1 48.7 29.9 24.0 30.6 31.3 11.2 25.7 28.5
	OR of poor health a	2.58 * 2.03 4.96 * 1.23 2.62 1.21 2.35 2.83 * 1.47 3.24 * 3.65 2.53 * 2.10 8.02 1.51 1.74 10.91 0.52 1.92 3.09 * 1.50 2.85 * 3.10 3.24 * 0.91 1.17 0.80 1.47
	For country codes, see appendix
	Chi-square test/logistic regression analysis:
	* : p<0.05;
	** : p<0.01;
	*** p<0.001;
	**** p<0.0001 a OR adjusted for sex and age (manual workers vs managers), each country being studied separately

Table 3

 3 Mediating factors according to occupational groups

	Men

**** J Epidemiol Community Health . Author manuscript **** J Epidemiol Community Health . Author manuscript

Table 4

 4 Contribution of mediating factors to social inequalities in health: results from multilevel logistic regression analysis

	Men		Women
	Poor health		Poor health
	OR (95 CI) a %	% b	OR (95 CI) a %	% b

[START_REF] Wilkinson | Social determinants of health: The solid facts[END_REF]

[START_REF] Wilkinson | Social determinants of health: The solid facts[END_REF]

[START_REF] Wilkinson | Social determinants of health: The solid facts[END_REF]

[START_REF] Wilkinson | Social determinants of health: The solid facts[END_REF]

[START_REF] Wilkinson | Social determinants of health: The solid facts[END_REF]

[START_REF] Wilkinson | Social determinants of health: The solid facts[END_REF]

[START_REF] Wilkinson | Social determinants of health: The solid facts[END_REF]

[START_REF] Wilkinson | Social determinants of health: The solid facts[END_REF]

[START_REF] Wilkinson | Social determinants of health: The solid facts[END_REF]

[START_REF] Wilkinson | Social determinants of health: The solid facts[END_REF]


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Bernard Jabiol

Terrestrial humus forms: ecological relevance and classification

The Humus form, i.e. the part of the soil which is influenced by organic matter [START_REF] Brêthes | Classification of forest humus forms: a French proposal[END_REF], has been recognized for a long time as the seat of most biological and physico-chemical processes essential to soil development and terrestrial ecosystem functioning. This concept applies to every kind of soil the upper part of which (the topsoil) is not permanently disturbed by human activity, i.e. to all non-tilled soils. In his seminal work, [START_REF] Müller | Studier over Skovjord, som Bidrag til Skovdyrkningens Teori. Om Bögemuld og Bögemor paa Sand og Ler[END_REF][START_REF] Müller | Studier over Skovjord, som Bidrag til Skovdyrkningens Teori. Om Muld og Mor i Egeskove og paa Heder[END_REF][START_REF] Müller | Studien über die natürlichen Humusformen und deren Einwirkung auf Vegetation und Boden. Mit analytischen Belegen von[END_REF][START_REF] Müller | Recherches sur les formes naturelles de l'humus et leur influence sur la végétation et le sol[END_REF] put the basis of a multifaceted assessment of humus forms, embracing pedology, sylviculture, biology, geology and climate. More than half a century later, [START_REF] Kubiëna | The soils of Europe[END_REF] classified European soils, considering the interaction between soil animals and vegetation as the driving force of soil development, geology and climate being the context. However, it is only recently that the concept emerged of humus forms as a digest of major processes which shape and stabilize ecosystems, pointing to the need for a better and worldwide assessment of diagnostic characters of humus forms [START_REF] Ponge | Humus forms in terrestrial ecosystems: a framework to biodiversity[END_REF][START_REF] Graefe | Humus forms as tool for upscaling soil biodiversity data to landscape level?[END_REF]. [START_REF] Ponge | Humus forms in terrestrial ecosystems: a framework to biodiversity[END_REF] considered Mull, Moder and Mor (Fig. 1) as three strategies of terrestrial ecosystems. Mull is characterized by an intense mixing of organic matter with mineral matter (i.e. the result of earthworm activity), stemming in a crumby and nutrient-rich organo-mineral horizon, Moder by a less rapid transformation of litter by litter-dwelling animals and fungi, resulting in the accumulation of organic humus, Mor by the slow transformation and accumulation of undecayed plant debris, with a sharp transition to the mineral soil. Mull, Moder then Mor correspond to a scale of decreasing nutrient availability and colder conditions, stemming in decreasing biological diversity and activity on siliceous substrates. Animals, microbes and plants are involved in positive (building forces) and negative (stabilizing forces) feed-back relationships most of them taking place in the humus profile. Look at the example of a forest mull: if the parent rock is rich in easy weathering minerals and the climate is mesic (not too cold, not too dry), then plant growth is rapid, including trees (site quality and productivity is high) and more exacting plants are allowed to grow (i.e. flower plants, with nutrient-rich and lignin-poor foliage, renewed annually). In turn litter (trees + forest vegetation) is nutrient-rich and will favoured more exacting microbes (bacteria) and animals (earthworms) the activity of which will contribute to favour tree growth and a diverse vegetation, which is typical of multi-layered forests. The same ring of causes and consequences explains why Mor, on the reverse side, is poorer in microbial, faunal and plant species and characterizes less productive but more conservative ecosystems: in familiar words, mull is a waster (the cicada of the fable), while Mor is a hoarder (the ant of the fable), but each of them allows a safe use of resources offered by geology and climate. Hence, the indicator value of humus forms.

MULL MOR TANGEL AMPHI MODER

Based on the knowledge accumulated on the relationships between morphological, biological and physico-chemical features of humus forms, several attempts have been made to classify them on the base of characters discernable to the naked eye directly on the field, and to derive from them properties at the ecosystem level (site quality assessment). Among many others we want to cite [START_REF] Delecour | Essai de classification pratique des humus[END_REF], [START_REF] Green | Towards a taxonomic classification of humus forms[END_REF] and [START_REF] Brêthes | Classification of forest humus forms: a French proposal[END_REF], the latter concept of humus forms and diagnostic horizons being included in the 'Référentiel Pédologique' [START_REF] Baize | A sound reference base for soils: the "Référentiel pédologique[END_REF]. Since that time, the need emerged of a common classification system at the European level, which could be compatible with the World Reference Base for Soil Resources (FAO, 2006).

Fig. 2. Mull as an attractor for humus forms in terrestrial environments

A network of European humus researchers was founded in Trento (Italy) in 2003, gathering 25 specialists coming from eight European countries. Since this date, the Humus Group met each year in different countries, to exchange knowledge, discover humus forms in new ecological conditions and to progress in harmonizing humus form concepts. New terrestrial humus forms were given names, such as Amphi [START_REF] Graefe | Gibt es in Deutschland die Humusform Amphi?[END_REF][START_REF] Galvan | Humus components and soil biogenic structures in Norway spruce ecosystems[END_REF], others were redescribed, such as Mor and Tangel (Fig. 1), and soil organisms were recognized as main agents of soil structure [START_REF] Graefe | Humus forms as tool for upscaling soil biodiversity data to landscape level?[END_REF]. The widest possible array of humus forms was covered, from southern to northern Europe, from seashore to high mountains, from dry to damp environments [START_REF] Zanella | Toward a European humus forms reference base[END_REF]Zanella et al., in prep.). Figure 2 exemplifies the concept of Mull as an attractor for terrestrial humus forms in forest environments, and its deviation under harsher environmental conditions.

On calcareous substrates Amphi is a twin humus form showing both characters of Mull (crumby organo-mineral horizon) and Moder (accumulated organic humus), due to a seasonal alternation between phases of high and low biological activity in strongly seasonal Alpine and Mediterranean environments. Tangel, still badly known from a biological point of view, expresses particular characters at high elevation and on hard calcareous rocks, where litter is out of reach of soil decomposer activity for most of the year and invertebrates cannot dig through the parent rock.

Fig. 3. Morphological and biological characters of the five main terrestrial humus forms prevailing in Europe

Main morphological and biological characters of Tangel, Amphi, Mull, Moder and Mor are summarized in Figure 3, which shows that the variety of humus forms known in Europe can be ascribed to several possible combinations of annelid oligochetes (earthworms, enchytraeids) the activity of which is of paramount importance for the building of soil structure [START_REF] Brown | How do earthworms affect microfloral and faunal community diversity?[END_REF]. Undecayed litter, fragmented litter, humified litter and the underlying mixture of organic and mineral matter are currently called OL, OF, OH and A, respectively. Prefixes such as 'eu' (normal, perfect) or 'dys' (atypic, degraded) are used to characterize humus forms at a subordinate level of classification once characters of main humus forms have been defined. The size of aggregates (invertebrate faeces) is indicated by prefixes 'micro' (<1 mm), 'meso' (1-4 mm) and 'macro' (>4 mm). The presence or absence of traces of faunal activity in horizons is described by suffixes 'zo' and 'noz', respectively. This flexible classification of horizons and profiles allows a wide variety of humus forms to be described and labelled, even when new to science.

The combination of geology (here expressed by pH) and climate (here expressed by rainfall and temperature) may help to explain the variety of humus forms found in European terrestrial environments (Fig. 4). Beside being a need for those people who want to describe the topsoil in terms clearly undestandable by everybody, the classification of humus forms may also help to put a diagnostic to the welfare of ecosystems. In this direction, the Humus Index, obtained by scaling humus forms of acid soils from Mull to Mor (see upper row of Figure 1), proved to be correlated with soil physico-chemical variables, stand properties and floristic composition of various temperate forest ecosystems [START_REF] Ponge | Humus Index: an integrated tool for the assessment of forest floor and topsoil properties[END_REF][START_REF] Ponge | Humus Index as an indicator of forest stand and soil properties[END_REF][START_REF] Lalanne | Opposite responses of vascular plant and moss communities to changes in humus form, as expressed by the Humus Index[END_REF]. Humus forms have been shown to be good indicators of present and past climate conditions and thus could be used for predicting future trends of global climate change [START_REF] Egli | Effect of north and south exposure on organic matter in high Alpine soils[END_REF][START_REF] Egli | The effects of exposure and climate on the weathering of late Pleistocene and Holocene Alpine soils[END_REF]. Hence the need for more expert tools based on a finer characterization of humus forms.

Fig. 1 .

 1 Fig. 1. The five main terrestrial humus forms prevailing in temperate ecosystems (bar = 10 cm)

Fig. 4 .

 4 Fig. 4. The five main terrestrial humus forms in a 3D frame of environmental conditions prevailing in Europe


Carina Furusho
email: carina-yumi.furusho@lcpc.fr

Katia Chancibaultt
email: katia.chancibault@lcpc.fr

Hervé Andrieu
email: herve.andrieu@lcpc.fr

FURUSHO et

Keywords: Flooding, modelling, suburban, runoff, drainage network 2010_04_02_01-40-55_paper_CFurusho.doc

Due to the expansion of urbanization, peri-urban zones face a quick land-use change. The control over this phenomenon has become a major issue for flood and water pollution management. Nevertheless, so far we are still on the pursuit of a well adapted model to these particular basins. We aim to develop such model by studying the Chézine basin, in the framework of the French national project AVuPUR (ANR-VMCS, 2008-2010). A 7year data analysis unveils a specific behavior: first, rain events displaying one single peak produce one or two distinct peak discharge on the hydrograph ; second, the lag-time of the basin, usually close to 1 hour, sometimes exceeds 6 hours. Based on geomorphologic and hydro-meteorological data analyses we made some hypotheses to explain the different shapes that the hydrological response of the Chezine Bassin may present. The localization of urbanization throughout the basin and its pre-event moisture state seem to play a crucial role on the variability of hydrological responses. The application of the First Differenced Transfer Function confirms the existence of different shapes of transfer functions for the basin according to its initial moisture state. Therefore we conclude that the hypotheses here presented should not be neglected in the current pursuit to develop a well adapted model for suburban river basinsWrite your abstract here here

INTRODUCTION

Suburban catchments have been facing many problems due to the fast land-use change that accompanies the worldwide phenomenon of urbanization. Conversion of land into industrial and residential uses significantly alters hydrological characteristics of land surfaces modifying pathways and rates of water flow. Bhaduri and al. (2000) assessed many impacts faced by basins located in urbanizing areas, emphasizing the increase of downstream flooding and the decrease of long-term deep and shallow groundwater supply. They also suggested that these consequences are enhanced by faster runoff from impervious surfaces and engineered drainage systems. In spite of these important issues, peri-urban rivers have been the object of only few studies so far. O'Loughlin et al (1996) raise important points to consider when combining rural and urban models. To keep it short, here we mention two of them: (1) topography, soils and vegetation have an important influence on the hydrological impacts of urban development; (2) urban impacts are greatest for low intensity storms because in rural areas losses small storms are relatively large, but impervious areas will always produce runoff. Valeo (2000) considered these remarks developing TOPURBAN, a modified version of the well known model for rural catchments TOPMODEL (Beven and Kirkby, 1979) so that the new model is also adapted to urbanized areas. Her model introduces a linear reservoir for describing the runoff over impervious areas, as in classical urban models (Nash, 1957;Cruise and contractor, 1980;Rao et al, 1972), but keeps the variable source area concept (Dunne et al. 1975;O'Loughlin 1996) largely used for rural and natural catchments. These source areas correspond to the saturated surfaces that produce runoff immediately under rainfall. The spatial distribution of these saturated contributive areas is commonly based on a topographic index (eq.1) used to determine and localize the regions that are more likely to saturate before the others; either because they drain a greater area, or because the region has a weaker slope than the others.

TI = ln

upstream area slope eq. 1 TOPURBAN presented better results over urbanizing basins than TOPMODEL and other conventional hydrological models (Valeo, 2000). Nevertheless, studies reveal that its simulations do not reach high verification efficiencies (Valeo, 2000). Thus the hydrological response of suburban catchments has still not been successfully reproduced by existing models so far. An example of this particular kind of basin is the Chezine river basin (Nantes, France), in which urbanization spreads heterogeneously over natural surfaces. The purpose of this paper is to explain particularities observed in the outflow hydrographs of the Chezine basin, capturing the essential features of the catchment's hydrological response. This work has been carried out within the context of the research project "Assessing the Vulnerability of Peri Urban Rivers" (ANR-AVuPUR), which aims to improve the knowledge in urbanizing catchments and ultimately develop an entirely adapted hydrological model for suburban river basins (Braud et al., 2009).

A classical method to apprehend the hydrological response of a basin based on observed data is the First Differenced Transfer Function -Excess Rainfall and Unit Hydrograph by a deconvolution Iterative Identification technique (FDTF - ERUHDIT, Duband et al. 1993). The FDTF applies the classical unit hydrograph concept for river basins, identifying the transfer function according to observed rainfall-runoff data. The method has been the object of several research studies (Nalbantis et al 1995, Rodriguez -Iturbe & Valdes, 1979) and has been applied in different contexts (Wendling, 1992;Rodriguez et al., 2003). We can thus assume that the method is a good indicator to verify the pertinence of our hydrological functioning hypothesis. This paper is organized in five sections: the first one provides an overview of the research area.

The second section describes the most important results of the database analysis leading to some hypotheses on the catchment's hydrological functioning. These hypotheses will lead us to a 3step methodology based on geomorphologic data. The description of this simple model will then be followed by the results of the FDTF applied on 2 different types of rainfall events that were identified among the Chezine hydrological responses. Finally, the last section presents conclusions and the perspectives for the ongoing project and related studiesTitle style = Major Headings Introduction -describing the background of the work and its aims.

The Chézine catchment

Covering an area of 29 km 2 , the Chezine river basin is located in the northwestern suburbs of Nantes, France. The Chezine River follows a south-easterly course and covers a distance of 15km from it's source at Saint Etienne-de-Montluc to it's confluence with the Loire River at Nantes. The watershed receives approximately 800mm of precipitation annually and the amount of cumulated rainfall is in general almost two times greater during the winter than in summer. The region has a mild year round temperature. The average temperature during the winter is 5°C and during the summer, the average is around 18. 5°C (www.meteofrance.fr, 2009). Due to these climate differences according to the season, the catchment is drier in the summer and quite wet during the winter. This wetness variation is clearly noticeable on field observation and has a relevant influence on the catchment's hydrologic behavior. The predominant rainfall type over the region is the frontal rainfall, from west to the east. Given the position and size of the catchment, the spatial structure variation of the precipitations is thus negligible in most of the cases. Nevertheless, whenever we find a particular behavior that cannot be explained by the topography and morphology of the basin, we set the data apart to be carefully analyzed with radar images.

The systematic analysis of radar images for all events will be performed later on in the project, for simulations with the complete hydrological model that will be developed.

The basin is equipped by a rain gauge and a hydrometric station both run by Nantes Metropole since January 2001. The rain gauge measures the total amount of rainfall every five minutes while the hydrometric station has a variable time step measurement, according to the variation of the water level (it takes measures every minute when the water level is changing and every hour when it doesn't detect enough variation on the water level).

The topographically-defined Chezine catchment (Figure 1) is extracted from a 20m resolution digital elevation model (DEM), supplied by Nantes Métropole. A complete urban database (roads, buildings, etc) has also been made available by the same local administration for this research project. The analysis described in the next section is essentially based on this dataset.

DATABASE ANALYSIS

The main objective of the database analysis was to identify particular behaviors and simple predictors to characterize them. From the 7-year rainfall-runoff available data set 295 events have been extracted, presenting a total precipitation superior than 2mm. 50 events among them were then selected. The criterion for their selection was to have an exploitable set of measures. Events that are superposed to others or those that have even one single bad measure for rainfall or outlet flow were rejected. Too long rainfall episodes or too weak outflow values have also been excluded. The observed hydrogrammes unveil a specific behavior. First, rain events displaying one single peak can produce two distinct discharge peaks on the hydrograph. It can be observed for instance on the event of october 2007 represented by the hydrograph on figure 2 In order to explain these behaviors, the start point of the study was evaluating the variability of the flow coefficient for different rainfall episodes on the Chezine basin. The flow coefficient (FC) is a traditional practical tool in engineering hydrology (Gottschalk et Weingartner, 1998).

In the classical 'rational formula' (Dooge, 1957) it is considered to be a constant, differing in value according to the catchment's morphology and land cover. Here, it is defined as the proportion of discharge volume from the total rainfall volume for each rainfall episode (equation 2). Erreur ! Des objets ne peuvent pas être créés à partir des codes de champs de mise en forme. eq. 2 A potential indicator of the basin dynamics is the pre-event discharge at the outlet (PED), which is commonly used to represent the soil moisture before each rainy episode. The PED is frequently considered as a proxy of state of the groundwater store (Graeff et al, 2009). The relation observed between PED and FC for the Chezine dataset (figure 3) suggests that the events could be devised into 2-groups with different behaviors: "dry episodes" and "wet episodes". In figure 6, the 37 dry episodes, with a PED inferior than 0,2 m 3 /s, are represented by the bar on the left. To the right, the larger bar represents the 13 events that have a PED superior or equal to 0,2 m 3 /s. The 37 "dry episodes" present a RC close to 0.05, the mean RC value of the group, whereas the "wet" ones are more dispersed. A hypothesis to explain the uniformity of the first group is the presence of a relatively constant proportion of runoff generating surfaces. If we assume that rural (or natural) surfaces in a dry condition retain or infiltrate all the precipitated water, the "constant portion" generating runoff would be the urbanized impervious surface. Meanwhile, when the soil is already wet before the rainfall episode, saturated rural surfaces of variable extension also contribute for the runoff generation. The definition of the extension and localization of these saturated rural surfaces was based on the variable source area, widely used by hydrologists in TOPMODEL (Beven and Kirkby, 1979) as it mentioned before. The next section describes how these hypotheses were considered for elaborating a simple method for simulating the discharge at the outlet due to the runoff generation distribution.

METHODOLOGY

The model is based on a natural water pathway guided by its topography and respecting the gravity law. Using a digital elevation model (DEM) with 20m resolution mesh and the unidirectional D8 algorithm (O'Callaghan J. and Mark D., 1984) we have extracted the catchment's topography and its hydrological network. The objective of the simulation developed at this point is not to achieve the most precise results but to apprehend the overall hydrograph shape based on a simple physical model. In order to verify the hypothesis listed in the last section, our choice was to reproduce the dynamics of the runoff over the basin with a simple 3-step geomorphologic model, known as 'isochronal simple transfer' as described by Estupina (2004). Using neither complex theories nor overparameterized calibrations the aim is to minimize misleading factors to better apprehend essential processes and features of the hydrological responses observed in this suburban catchment.

The first step of the methodology consists on the determination of the pixels that produce quick flow. Next, we calculated the hydrological distance to the outlet from each of these 'contributive' pixels. Finally, in order to obtain the time evolution of the outflow we affected a constant flow velocity for the stream channels and another slower one for hill slope flows. Urban runoff coefficient corresponds to the angular coefficient of the linear adjusted graphic on figure 7. Thus the urban coefficient is 0,06. The initial losses over urban areas are estimated by the interception of the graphic with the horizontal axis (2mm). Meanwhile, over natural surfaces, the losses vary depending on the initial moisture state of the catchment. According to the hypothesis defined on the previous section, the impervious urban portion of the cells is always a source of runoff. For defining the imperviousness of each cell of the catchment mesh, a GIS layer of streets and a layer of buildings were taken from the urban data bank. These impervious surfaces correspond to the contributive pixels for dry episodes, and thus the first step of the model for this case (dry moisture state) is defined. The distribution of these pixels according to their distance to the outlet is represented on figure 8. This morphological signature is known as Impervious Function (Gironas, 2007), and it is similar to the Width function (Rodriguez-Iturbe & Valdes, 1979), but only considers the impervious surfaces of the catchment. It is possible to identify the first peak of the graphic corresponding to the city of Nantes and Saint Herblain (figure 1), that are found at the third sector closest to the outlet (within 5km). The second elevation corresponds to Sautron (figure 1), that is the urbanization node located at about 10km from the outlet. The overall shape of the imperviousness function is coincidently bimodal suggesting that the source of the dual mode hydrographs often found among the analyzed events may come from the distribution of imperviousness throughout the catchment, at least for episodes when the initial moisture state is rather dry. Another hypothesis drawn from the dataset analysis (section 2) was that urban contribution is constant for all events. By doing so, we can compute the rural variable source area extension by subtracting urban contribution from the observed total flow coefficient.

The second step of the model requires defining the spatial localization of the contributive area: the impervious cells and the natural saturated cells. The first ones have been mapped from the urban GIS data bank. In order to localize the natural cells that are more likely to saturate before the others, we used the concept of topographic index (Beven & Kirkby, 1979). It depends on the upstream contributing area of each pixel and decreases with its slope (eq.1). A topographic index threshold is calculated for each class of episodes depending on their flow coefficient. All the natural pixels with a topographic index superior to the threshold determined for the event are considered to be saturated and thus contribute to the runoff. The third step of the model was accomplished in a very simplified way because the objective was to first investigate the sources of runoff production before going further into flow dynamics issues. Velocity values most usually found in the literature for hill slope and channel stream flows were tested and compared to observed data for model calibration. Rural hill slope flow was considered to be about 10 times slower than channel stream flows (river and urban pixels). The velocities that produced the best results, according to the Nash criterion (Nash & Sutcliffe, 1971) were then chosen to be applied on further simulations.

RESULTS AND DISCUSSION

According to the methodology presented in the last section, the outlet discharge responses were obtained (figure 7) for a unit rainfall applied in different wetness contexts. The moisture state is represented by the flow coefficient, remembering that their relation has been discussed on section 3 (figures 3 and 4). The hydrograph observed on figure 7.a may explain bimodal responses as the one shown on figure 2a. The two peaks have been identified in the description of the impervious function (figure 6). As the flow coefficient increases, the second peak grows bigger and becomes relatively more important than the first peak, as shown on figure 7. While the first peak is composed essentially by runoff from the first urban agglomeration closer to the outlet (figure 1), the second peak is probably composed partially by the flow that comes from the second urban agglomeration (Sautron, figure 1) and in addition by rural saturated areas when its moisture is wetter. The saturated rural zones are determined according to the variable source area (Beven and Kirkby, 1979). The wetter the soil is the larger the source area will be. Moreover, the second peak occurs 6 hours after the rainfall. This may explain why the lag time seem to be postponed 6h when the soil is wet before the rainfall event. The first peak being much smaller than the second one ends up 'disappearing' from the hydrograph by the effect of the dispersion of the rainfall peak (figure 2b). Figure 8 shows the FDTF for different groups of rainfall event types, once again according to their flow coefficients. The hydrological response when the catchment is rather dry and the flow coefficient is weak (around 0.02) presents a clear peak an hour after the rainfall impulsion. As we take stronger flow coefficients, the first peak is still found an hour after the rainfall impulsion but it relatively 'decreases' comparing to the rest of the hydrograph, specially comparing to the second elevation of the curve. Therefore we can conclude that the tendency of these curves, as the coefficient increases, is quite similar to the results obtained with the geomorphologic simple transfer presented on figure 7. The second peak also appears and grows bigger as the first peak retracts with the increase of the flow coefficient value that characterizes each group of episodes. The main difference between the two groups of unit hydrographs (geomorphologic on figure 7 and FDTF on figure 8) is the second peak of dry events that appears on geomorphologic transfer function and not on the FDTF one. When we deal with weak rainfall over a rather dry soil, the contribution of the second node of urbanization upstream (Sautron on figure 1) is probably weakened by the effects of diffusion that have not yet been included to the simple transfer methodology applied in this work. Results and Discussion -a clear presentation of experimental results obtained, highlighting any trends or points of interest.

CONCLUSIONS

In the context of the research that ultimately aims to develop a well adapted hydrologic model for suburban basins, this work focused on determining the main contributive sources of runoff over the catchment. Our objective is to explain some particular behaviors observed by investigating this process and find indicators that trigger different hydrological responses to rainfall on a basin. The Chezine rainfall-runoff hydrographs showed that the basin often presents a bimodal response. Another interesting observation is that the peak time can vary from 1h to 6h. We have used a simple model to explain these particularities, identifying relevant parameters and features that must be considered in a future model. Based on the results of a hydro-meteorological dataset analysis, two hypotheses have been drawn to describe the behavior of the basin according to its initial moisture state. When the soil is dry, natural surfaces infiltrate, store and evaporate all the rainfall. Therefore runoff is produced entirely over impervious surfaces. However, when the basin is wetter, part of the rural (or natural) surfaces are saturated and generate runoff as well. We thus complete the second remark extracted from O'Loughlin et al (1996) in the introduction of this paper: urban impacts are greatest not only for low intensity storms, but also for a drier initial wetness state of the basin. Both factors are extremely important because they imply relatively large losses over rural areas and thus the most important contribution to the outlet flow variation comes from the urban zones. The simple 3-step geomorphologic model allowed us to draw based on these hypotheses different unit hydrographs according to the flow coefficient, which was shown to be closely related to the initial moisture state. This study suggested, by the means of the imperviousness function (Gironas, 2007), that the localization of imperviousness over the basin could be responsible for the dual-mode response for dry initial state episodes, when urban contribution is preponderant. When the basin is wetter the contribution of the rural saturated areas increases in addition to the second urban zone upstream (Sautron, figure 1). The greater the flow coefficient is the bigger second peak will be. This might explain why the lag time seems to increase in some events (as the one on figure 2.b): the first peak (an hour after the rainfall), being much smaller than the second one (6h after the rainfall), probably ends up 'disappearing' from the hydrograph by the effect of dispersion. The application of the FDTF produced a similar trend of curves as it was observed on simulations, corroborating the hypotheses made on runoff generation for drawing these geomorphologic transfer functions. The differences observed can be explained by the diffusion effects of the routing that were not yet considered at this point. For a complete attempt of hydrological model it is thus important to consider the diffusion effects using for instance the kinematic wave theory (Moussa, 1996) instead of the simple transfer for routing the water flow. This work was meant to identify important characteristics that must be considered when developing a complex, detailed model for suburban catchments. It was shown that it is indeed essential to distinguish and well represent both urban and rural areas. The role of the soil wetness initial state in models for peri-urban basins has also been proved to be crucial, as we have different transfer function shapes depending on their flow coefficient that varies according to the basin initial moisture state. Acknowledgements: The AVuPUR project was funded by the French Agence Nationale de la Recherche (ANR) under contract ANR-07-VULN-01.

Figure 1 .

 1 Figure 1. Chezine catchment indicating the location of the rain gauge and the hydrometric station at the outlet. The grey areas correspond to the urban database layers superposed (roads and buildings).

  .a. Second, the lag-time of the basin, usually close to 1 hour, sometimes exceeds 6 hours, as shown on figure 2.b.

Figure 2 .

 2 Figure 2. Observed discharge (m3/s) in pink lines and averaged 15 min observed rainfall (mm) represented by blue bars on (a) 17 October 2007 and (b) on the 21st -22nd of March 2001. The time-lag is indicated by double arrows.

Figure 3 .

 3 Figure 3. Correlation between the flow coefficients and the pre-event discharges for 50 rainfall episodes over the Chezine basin in the period from 2001 to 2007.

Figure 4 .

 4 Figure 4. : Flow coefficient values for dry events (PED <0.2 m3/s) and for wet events (PED>=0.2 m3/s). The bars represent the interval of values for 50% of the events. The vertical extension lines represent the edges for 80% of the events. The horizontal lines represent the mean FC value of each group.

Figure 5 .

 5 Figure 5. The angular coefficient of the linear adjusted graphic (total runoff versus precipitation) is an estimation of the urban runoff coefficient. There are 2mm of initial losses over the urban zone according to this graphic.

Figure 6 .

 6 Figure 6. The Impervious width function of the Chézine basin

  among different FDTF according to the runoff coefficient value.

10thWWW YES, Arcueil, France, 31 May -4 June 2010 FURUSHO et al

• Bhaduri, B., Harbor, J., Engel, B. and Grove, M. (2000), Assessing Watershed-Scale, Long-Term Hydrologic Impacts of Land-Use Change Using a GIS-NPS Model. Environmental Management 26(6):643-658. • Beven, K. & Kirkby, M. (1979) A Physically Based, Variable Contributing Area Model of Basin Hydrology. Hydrological Sciences Bulletin , 24: 43-69. • Braud, I., Chancibault, K., Debionne, S., Lieme Kouyi, G., Sarrazin, B., Jacqueminet, C. (2009) The AVuPUR project (Assessing the Vulnerability of Peri-Urban Rivers) : Experimental and modelling strategy. Geophysical Research Abstracts,Vol. 11, EGU2009-3353-1 • Cruise, J.F. and Contractor, D-N. (1980). Unit hydrographs for urbanizing watersheds, Journal of the Hydraulics Division Proceedings of the American Society of Civil Engineers, 1û6, (HY3), pp. 440-445. • Dooge, J.C.I. (1957) The rational method for estimating flood peaks. Engineering. 184. 311-313, 374-377. • Duband, D., Obled, C., Rodriguez, J., (1993)


Aliki-Myrto Perysinaki
email: almy.pery@gmail.com

How do waterscape projects combine landscape design and natural processes to create dialogues that engage both culture and nature? The case of the Boston park system and the solar city

Keywords: Waterscape, urban ecology, water infrastructure systems

The transformation of nature through urban development has resulted in a disturbed ecosystem. Urban infrastructure built to contain and overpower natural processes has finally been particularly harmful. In recent years, some ecologically and culturally conscious design practitioners have tried to develop a way to combine the processes of nature and the aesthetic qualities of water in order to create urban spaces that bring people together in embracing the nature and culture of a place. These types of projects are called "waterscapes." Waterscapes are constructed water features in urban public squares and parks: they celebrate the role of water in our urban landscapes and allow people to experience the qualities of water through touch, sight and sound. The rationale behind this way of treatment of water resources is to produce sustainable and beautiful urban spaces where people can engage with the pleasures of water.

INTRODUCTION

Water has supported the landscapes of our civilizations. Earth's evolution and transformation is due to water. Nowadays we are facing complex urban development processes leading to completely new challenges concerning the management and design of urban infrastructure systems and landscapes. Water can improve spatial quality by creating an attractive and spacious place.

Landscape architects, planners and designers know better the fundamentals of water and its power in transforming our landscapes. This means that it is water that allows us to reaffirm our commitments to landscape. The potentials of nowadays water infrastructure systems for shaping urban form and meeting human, ecological and aesthetic objectives have almost been lost. The processes of extreme and unpredictable urban growth and decline are leading to huge challenges concerning the affordability and functioning of present water conceptions and demand new innovative solutions. The appearance of water infrastructure systems, further accentuating natural physical landscape structure became a visual and spatial component of structuring and organizing cultural landscapes. The relationships between natural and human processes are based on a deep understanding of complex processes. Water infrastructure was able of creating synergies with other important urban functions, serving as an open space network for social needs. However the increasing pressure, intensity and speed of urbanization led to the disappearance of any visible forms of water infrastructure in most cities.

The transformation of nature through urban development has resulted in a disturbed ecosystem. Among the many consequences of a disturbed hydrologic cycle are polluted waterways because of sewer overflows and urban runoff, subsiding land due to a diminished water table, and city dwellers that are deprived of experiencing the fundamental life force of water. Urban infrastructure built to contain and overpower natural processes has finally been particularly harmful. After these observations, we need to realise that urban structures will have to be reexamined in order to achieve an urban landscape where water's existence is going to be evident.

Contemporary landscape and urban design is usually looking at urban landscapes with mainly aesthetic considerations constrained by an attachment to the picturesque. In order to change their current situation and become more attractive, most cities are developing programs to open up their inner-city waterfront locations on canals and rivers. Landscape architects and designers have not being questioning themselves about the technical nature of infrastructure. Rather than leaving this field to engineers, the profession of landscape architecture should take a leading part in the reconstruction and development of urban infrastructure systems. The strength of landscape architecture lies in its ability to extend our understandings of infrastructure, linking the performance of natural processes with engineering and urban design strategies. In order to manage to create an infrastructural landscape, it is basic to develop a more profound and practical knowledge about ecological systems and a more developed cooperation between different disciplines and practitioners combining the work of architects, engineers and urban designers.

Combining the built and the natural will possibly allow to new logics towards the cultivation of infrastructural landscapes as a base of sustainable urban and regional form.

MATERIAL & METHODS

Liquid perception is the promise or implication of another state of perception. According to his cinema theories, Gilles Deleuze considers that liquid perception is "more than human perception, a perception which no longer has the solid as object, condition or milieu. It is a more delicate and vaster perception, a molecular perception" (Deleuze, 1986). In this paper the aim is to show the importance of moving towards a systemic approach to urban ecosystem by introducing a water-urbanism. The examples that are going to be presented explicitly demonstrate how water shapes the urban landscape, how projects allow people to see, hear, touch and experience water moving through segments of the city.

In recent years, some ecologically and culturally conscious design practitioners have tried to develop a way to combine the processes of nature and the aesthetic qualities of water in order to create urban spaces that bring people together in embracing the nature and culture of a place. These types of projects are called "waterscapes." Waterscapes are constructed water features in urban public squares and parks: they celebrate the role of water in our urban landscapes and allow people to experience the qualities of water through touch, sight and sound. The rationale behind this way of treatment of water resources is to produce sustainable and beautiful urban spaces where people can engage with the pleasures of water. Waterscapes as fountains and open waterways are examples known from ancient times, proving how closely urban design has been linked with water. This relationship can be traced from antiquity through the Middle Ages arriving finally to modern times. Water was not only combined with the city's prosperity but as well was used to express a living relationship between a city and its surroundings. For example, the small-scale garden or park is the most comprehensive form of manmade landscape. It shows us the pertinence of paradigms and of ways to understand how landscape works: being able to imagine water spaces with more complex requirements and more complex structures according to topography demands and ecology conditions. But still, water remains one of the key questions that has to be answered in order to move towards a sustainable relation assuring the stability of urban ecosystems. We need to move towards a sustainable water culture. Natural water has to be combined with aesthetic creations in order to achieve urban ecological waterscapes: the combination of the scientific with the aesthetic can assure design strategies concerning water's transformation. Protecting and managing of a landscape require noticing, conserving and leading each landscape component. Water resources are the most important natural values that complement the landscape and provide ecological cycle. In this context: i.

Recognition of the diversity of water resources to include aesthetics and its inclusion in water resource design and planning will contribute sustainability. ii.

Water resources should be considered as a whole and all cultural studies related should be planned and managed by focusing on these natural values. iii.

The water should be able to be used as a visual resource value for planning at macro level and design studies at micro level.

EXEMPLES

In this paper we will present two cases, located in different periods, illustrating the principles of sustainable urbanism, where water principles are among the priorities of each proposition.

The Boston Park system Back Bay Fens

The first example is the Boston park system designed by Frederick Law Olmsted. Frederick Law Olmsted was an American journalist, landscape designer and father of American landscape architecture. He was famous for designing many well-known urban parks, including Central Park and Prospect Park in New York City. He developed a style of landscape design that still exerts a strong influence on his profession. Olmsted believed that the rural, picturesque landscape contrasted with and counteracted the confining and unhealthful conditions of the crowded urban environment and served to strengthen society by providing a place where all classes could mingle in contemplation and enjoyment of the pastoral experience. He sought to screen his "pleasure grounds" completely from the intrusions of daily life by screening them with thick plantings along their borders, separating and excluding commercial traffic, and discouraging all usage of the grounds which were not in harmony with this goal. He also strove to bring the landscape as close to as much of the urban population as possible, so that all could benefit from it. He designed parks and public recreation grounds trying to create spaces that had an important psychological effect to their users, planning every detail in a specific way. He also conceived of entire systems of parks and interconnecting parkways to connect certain cities to green spaces. The success of these larges-scale urban parks was the implementation of a new vision of urban form that led finally to the application of an ideology of moral and civic improvement in other areas of urban design. Modern technology and science made city a safe place to live. Improvements in water supply, water treatment and sewerage benefitted the health of the cities increasing their comfort and safety.

In the late 19th and early 20th centuries, Frederick Law Olmsted devised strategies that both solved complicated drainage problems and provided cherished public open space as in the Back Bay Fens [figure 1]. His conceptions for metro-wide park systems, linked by scenic parkways, took its most comprehensive form in the 1890's proposal for Boston regional park system. It is considered today as a park that marked the culmination of the evolution of the naturalistic urban landscape. The plan proposed by Olmsted evoked the scenery of nearby salt marshes. To manage this he had to provide ingenious solutions to a series of problems involving sanitary engineering, traffic engineering, recreational facilities and institutions for scientific educations. The project's site (Back Bay Fens) was a noxious, sewage-soiled mudflat. For Olmsted the project had a strong sanitary engineering aspect that should be resolved. In order to keep water permanently in the area, he created a basin with a tidal gate. The problem was that the two major steams that fed into the Fens would cause devastation to the basin in case they flooded. The solution he proposed was for the streams to bypass the Fens through conduits that could carry the ordinary rate of flow and to plan the Fens to handle the overflow during freshets. In order to create a soft vegetated edge around the basin, he had to solve two problems. First of all he had to provide adequate space to hold the floodwaters and have at the same time room left for natural growth. Secondly, he had to protect the natural shoreline from erosion by surf during storms. The proposal he suggested was to make gradually shelving banks and to construct wide islands slightly above the usual water level which would be planted. In flood conditions a full fifty acres would be covered by water, but the plantings would slow the serf's development. The water in the basin would be extremely high tide on the river after which a gate would allow the water level to fall as the ebb tide drained the river. This project, that gave Olmsted the opportunity to preserve stream ways in the midst of built-up areas, was linked to the Muddy River valley between Back Bay and Jamaica Pond [figure 2]. He proposed to narrow the river valley in some places in order to make the river follow a more graceful course and create a chain of picturesque fresh-water ponds. On the Boston side of valley he planned a public way that continued the walk, drive and ride system of Back's Bay design. On the other side he allowed more space for planting along the walks and drives. Between Jamaica Pond and Franklin Park the walk was extended by means of the Arborway consisting finally a multilaned parkway.

PERYSINAKI A-M Olmsted's plan for Boston's park system, known as the «Emerald Necklace» consists of several small parks that are linked by tree-lined roads called parkways. This concept of separate but connected parks provided a way to link newly-added areas to the traditional city center while providing several forms of recreation for area inhabitants such as pleasure driving, picnicking, and hiking [figure 3]. The solar city in Linz

The second example is the Solar City, in Linz (Austria). The Linz Solar City Project is an integrated solar village for 1300 households on the outskirts of Linz. The city of Linz assigned the task of designing the first 630 homes to architects of the calibre of Norman Foster, Richard Rogers and Thomas Herzog, who has been a pioneer of sustainable construction since the '70s.

The project is among the larger settlements built on the basis of the tenets of sustainable architecture [figure 4]. The basic principle underlying the project is the desire to promote low cost building methods internationally. The sustainability parameters include achievement of maximum possible density, maximum flexibility of types, and careful study of traffic routes to promote and facilitate pedestrian and cycle traffic. Individual homes are built to make the most of the lie of the land, with greenhouses, winter gardens, balconies and orientations that benefit from the climate and nature surrounding them. One of the parameters taken into consideration is energy supplies: the development was not supplied by the city's electricity grid but co-generate its own energy with "solar" installations which will, in the future, make the neighbourhood completely independent and even allow it to return part of its energy surplus to the city's energy grid. More particularly, the site is located close to the two rivers that pass by Linz: Danube and Traun.

The place was characterized by a typical landscape of water meadows. The aim was to transform the water meadows to a nature conservation area. This meant that the designers had to fend off threats to the nature conservation area without banning access but by controlling it. Rainwater was the first thing that had to be controlled: a system of channels, basins, ponds and streams, extending from the area near the buildings to the wooded meadows was thought. Rainwater is brought where possible to seep away and larger quantities of rain have their own channels or are fed to the raceway in north of the Solar City. Among the priorities were groundwater upgrading, the creation of permanent and temporary wet areas and finally support to the water regime in the river meadows. To protect the landscape, a range variety of different recreation areas, such as playgrounds, gardens and meeting places, was established between the Solar City and the nature conservation area. Furthermore, a park corridor or a "parkway" and facilities like a bathing lake, allotments and a sports center were thought to enrich the project [figure 5 and6].

CONCLUSIONS

As pieces of urban infrastructure, waterscapes respect and celebrate the hydrologic cycle of nature while simultaneously expressing the cultural importance of water for humankind. Waterscapes construct and repair all types of water features, from small to large features. They concentrate on introducing water features and water courses into the landscaping of an area. On one hand they can be natural elements that penetrate the city (rivers, lacks or the sea) which are taken into consideration in order to form the urban shape. On the other hand, waterscapes can be constructed: artificial creations are usually though during or after urban plantation. The addition of ponds, waterfalls and water features are for example inherent to the completion of any office, landscaped garden, entertainment area or focal point. These two categories can as well be combined. In both cases, making use of dynamic natural processes, the designed urban landscapes will work as artificial ecologies.

The most valuable contribution of design practitioners can be made at the first stage of a project to generate ideas with technical understanding and creative flair for the design, organization, and use of spaces. First of all, they have to conceive the overall concept and prepare the master plan, from which detailed design drawings and technical specifications are prepared. They can also review proposals to authorize and supervise contracts for the construction work. Other skills include preparing design impact assessments, conducting environmental assessments and audits, and serving as an expert witness at inquiries on land use issues.

Water is after all, a natural element and requires careful management. With careful harvesting, cleaning, use and re-use it can be (re-)considered as a liveability element to urban ensembles.

Figure 1 :

 1 Figure 1: Sylvester Baxter, Boston Park Guide

Figure 2 :

 2 Figure 2: Olmsted archives, Boston Park System

Figure 3 :

 3 Figure 3: A view of the park

Figure 4 :

 4 Figure 4: Solar City: masterplan

Figure 5 and 6 :

 6 Figure 5 and 6: Solar City: permanent and temporary wet areas

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10thWWW YES, Arcueil, France, June 2010, Urban water: resource or risks?

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