Peri-urban Catchment Research Articles

Terrain representation impact on periurban catchment morphological properties

Modelling the hydrological behaviour of suburban catchments requires an estimation of environmental features, including land use and hydrographic networks. Suburban areas display a highly heterogeneous composition and encompass many anthropogenic elements that affect water flow paths, such as ditches, sewers, culverts and embankments. The geographical data available, either raster or vector data, may be of various origins and resolutions. Urban databases often offer very detailed data for sewer networks and 3D streets, yet the data covering rural zones may be coarser. This study is intended to highlight the sensitivity of geographical data as well as the data discretisation method used on the essential features of a periurban catchment, i.e. the catchment border and the drainage network. Three methods are implemented for this purpose. The first is the DEM (for digital elevation model) treatment method, which has traditionally been applied in the field of catchment hydrology. The second is based on urban database analysis and focuses on vector data, i.e. polygons and segments. The third method is a TIN (or triangular irregular network), which provides a consistent description of flow directions from an accurate representation of slope. It is assumed herein that the width function is representative of the catchment’s hydrological response. The periurban Chezine catchment, located within the Nantes metropolitan area in western France, serves as the case study. The determination of both the main morphological features and the hydrological response of a suburban catchment varies significantly according to the discretization method employed, especially on upstream rural areas. Vector- and TIN-based methods allow representing the higher drainage density of urban areas, and consequently reveal the impact of these areas on the width function, since the DEM method fails. TINs seem to be more appropriate to take streets into account, because it allows a finer representation of topographical discontinuities. These results may help future developments of distributed hydrological models on periurban areas.

Addressing rural diffuse pollution in peri-urban agricultural catchments using the FarmFLOW framework: a study in the Pumicestone catchment

Diffuse pollution from agriculture is a major threat to downstream aquatic ecosystems in Australia. Integrated catchment management approaches in Queensland in the 1990s failed to alter farm practices to address this pollution. Action research was used to develop and implement a novel approach to peri-urban agricultural catchment management. The project developed and refined the FarmFLOW framework, which is an area-wide adaptive management approach to extension, specifically for high-value but high-risk peri-urban agricultural catchments that feature a diverse mix of land uses. Over four years, the project achieved its target of 30 per cent of producers adopting all the recommended best management practices. Further, over eighty percent of producers commenced a process of continuous improvement in their adoption of at least some new practices that reduce off-site movement of nutrients of concern by 2011. The project has demonstrated social and economic benefits to producers and a consequent reduction in risk of chronic algal blooms (Lyngbya majuscula) in receiving waters. Based on network and integrated catchment management theory, the project has created a hub for research, development and extension, while achieving industry development and natural resource management objectives.

Analysis of intensively used catchments based on integrated modelling

► An integrated immission based catchment model for peri-urban catchments is developed. ► Models for urban and rural parts and the water body are coupled via OpenMI. ► Water quantity and quality are modeled spatially and temporally detailed for urban and rural areas and the receiving water body. ► Results show that neglecting impacts from one area leads to significant errors. ► The developed model is freely available at http://bluemodel.org/. A model system that overcomes the separation of rural and urban areas for an integrated immission based modelling of catchments with complex land use is presented. To account for both the sewer system dynamic processes and the dynamics of single events in the runoff processes from rural areas, the model operates on a high temporal resolution and in continuous mode. The basic system structure and the rural areas are represented by means of a semi-distributed rainfall-runoff and pollution load model that allows for a user-specified spatial resolution. For each urbanized area within the catchment an urban hydrological pollution load model is used. This allows for a detailed assessment of the urban drainage structure even for multiple settlements within one catchment. Pollutant transport, mixing, and transformation processes within the receiving water body are modelled to account for accumulating and long-term effects. The model concept was applied to a real world case study. It was found that the consideration of all impacts is essential for an immission based approach. It can be concluded that a realistic description of the water body status can only be achieved by means of a detailed representation of both flow and mass transport processes in urban and rural parts of the catchment as well as the receiving water body in a high temporal and spatial resolution.

Do stormwater source control policies deliver the right hydrologic outcomes?

Summary The number of stormwater source control (SC) regulations adopted by local authorities is rapidly growing in many countries. We can expect that, in the near future, the hydrologic behavior of many urban and periurban catchments will reflect this diffusion. This paper discusses SC regulations through two complementary approaches: starting on three French case-studies, it analyzes how regulations are developed today and identifies a set of shortcuts in policy-making practices. Then, the hydrologic model of a periurban catchment in the Paris region is used to test the impacts that these regulations can produce if widely applied. The main finding is that inertia in policy-making, driving a singular focus on flow-rate based regulations, can produce negative impacts in the long-term. Further efforts on volume-based regulations are advocated, both in terms of research and policy-making.

Evidence of the impact of urbanization on the hydrological regime of a medium-sized periurban catchment in France

In this paper we explore several indicators to evidence the impact of land use change, and particularly of urbanization/artificialization on discharge series of periurban catchments. A first set of indicators is derived from the literature and describes the monthly and annual hydrological regime, low flows and high flows, and flow components. Statistical tests are also applied to assess the existence of trends/ruptures on the longest time series. In addition, new indicators, especially built to show the impact of sewer overflow devices (SODs) and infiltration into sewer networks are proposed. The method is applied to the Yzeron (150 km2) catchment, located close to Lyon city (France) where various discharge gauges with a variable time step are available on sub-catchments ranging from a few to 130 km2 (some of them nested), with a large variety of land uses (forest, agricultural land, artificialized areas). In addition, discharge is also measured in a SOD and a combined sewer network so that the relevance of the new proposed indicators can be assessed. In the largest sub-catchments, the results show a decrease of specific discharge from upstream to downstream corresponding to an increase of artificialized areas, except for high flows. When a SOD is present, the specific discharge is increased for frequencies larger than 50%, and the frequency of zero daily discharge is decreased. Waste water can be the only source of water in autumn month in a 4.1 km2 sub-catchment. Base flow is also decreased for the most urbanized catchments. Our results confirm the impact of SODs on the modification of the flood regime, with an increase of frequent floods, but a marginal impact on the largest floods, mainly governed by saturation of the rural parts of the catchments. The decomposition of the sewer discharge shows that, on an annual basis, infiltration in the sewer network accounts for 30% of the total discharge and runoff due to rainwater to about 40% (the remaining being composed of the waste water discharge). It can explain the decrease of base flow. Our analysis shows that, for periurban catchments, a long term monitoring of nested sub-catchments and infrastructures (SODs, sewer networks) with a small time step, is very valuable and provides data allowing a quantitative assessment of the impact of urbanization on the whole hydrological regime.

Hydrogeomorphic adjustments of stream channels disturbed by urban runoff (Yzeron River basin, France)

This paper presents a field investigation on hydrogeomorphic adjustments of small streams in a 147 km2 periurban catchment, the Yzeron River catchment located in France. The rapid development of periurban areas in the world is now considered as one of the main factor impacting river systems. Urban disturbances are most of the time associated with irreversible alterations of the hydrological regime, the sediment yields, with major ecological impacts and additional socio-economical costs. Nineteen stream reaches have been considered in this study, with drainage areas ranging from 0.2 to 33.9 km2 and total impervious areas ranging from 1% to 52% of the basin surface. A regional analysis was led in order (i) to quantify the hydrogeomorphic adjustments of stream channels in this periurban context, i.e. the ratios between observed values and reference/rural values; and (ii) to identify the main anthropogenic controlling factors of these adjustments. Results show that urban river channels experience a global enlargement, with a mean bankfull discharge ratio of 1.8, bankfull width and depth ratios of 1.3 and a bankfull area ratio of 1.8. This study also outlines the global increase of hydrogeomorphic adjustments with the increase of the fraction of impervious area and the level of disturbance of the flood regime. However, local anthropogenic factors seem to be much more relevant to explain the highest adjustment ratios at several river reaches (enlargement ratio up to 55). The vicinity of a river reach with road sewers and/or the urban areas is identified to be a very important factor that affects significantly the smallest streams (drainage area less than 5 km2). On the contrary, at several reaches no significant deepening or widening was observed although roads/urban sewers and urban areas were identified in their catchment. Several hypotheses are proposed, but additional works with new data (river monitoring) would be needed to propose management and/or restoration guidelines in periurban catchments.

Learning to manage quality in a multiple reservoir system: Contribution of a companion modelling approach

The development of water policies based on integrated water management principles promotes the development of multistakeholder platforms to manage water resources at catchment level. This is the case of the Alto-Tiete watershed, the urban catchment encompassing the Sao Paulo metropolis in Brazil. The dynamic pattern of peri-urban areas characterised by rapid major changes has led to complex management issues in which the quantity and quality dimensions of water are intertwined. Effective participation of a broad spectrum of stakeholders supposes that actors from different technical backgrounds have a better understanding of the social and biophysical interactions of the system concerned. This paper describes the role of participatory modelling and simulation as a way to provide a meaningful framework to enable actors to understand the interdependencies in peri-urban catchment management. A role-playing game, connecting the quantitative and qualitative dynamics of the resources with social interactions at catchment level, was developed and tested with members of the catchment committee. Monitoring of the sessions underlined the role of such a tool in learning about collective water management.

Elaboração multidisciplinar e participativa de jogos de papéis: uma experiência de modelagem de acompanhamento em torno da gestão dos mananciais da Região Metropolitana de São Paulo

O desenvolvimento de ferramentas de simulação, como os jogos de papéis, pressupõe a integração das várias representações e conhecimentos, o que garante a sua legitimidade e a possibilidade de os utilizar como plataforma de mediação na discussão dos conflitos socioambientais. Este artigo discute a utilização da abordagem de modelagem de acompanhamento no desenvolvimento de dois jogos de papéis sobre a gestão da água e do solo em mananciais periurbanos da Região Metropolitana de São Paulo (RMSP).

Suburbanisation of important aquifers in England and Wales: estimating its current extent

AbstractThe UK rate of conversion of rural into suburban land cover will increase as the UK population is projected to rise to 70 million by 2056, household size continues to decline and previously developed land becomes scarcer and less attractive. The resultant change in landuse will significantly impact underlying groundwater resources. Geographical information system (GIS) analysis is used to estimate the current extent of suburbanised land cover overlying locally and nationally important aquifers in England and Wales. The effect on groundwater catchments will be marked in southern, central and eastern England, where high groundwater dependence and intense pressure for new housing will inevitably lead to a rise in suburban land cover on periurban catchments that are currently rural land. Water resource planning implications would be better understood with more catchment‐scale research. Meanwhile, areas of aquifer most likely to urbanise by 2050 and public supplies most vulnerable to the consequent changes need identifying.

06/02456 Institutional arrangements for articulating land and water management in peri-urban catchment: example of the metropolitan region of Sao Paulo, Brazil: Ducrot, R. et al. International Journal of Water, 2006, 3, (2), 186–203.

Air quality data (O3, NO2, NO, CO and SO2) of two Greek coastal cities, Patras and Volos, were analyzed and compared to evaluate: (a) the exceedances of air quality EU threshold values, (b) the diurnal patterns of air pollutants and (c) the “weekend effect” on ozone levels.High ozone levels, close to the thresholds for human health and clearly above the threshold for the protection of plants and ecosystems, were observed in Volos. O3 levels in Volos were higher than those in Patras. NOx levels in Patras were significantly higher than the limits for human health and plants’ protection. Both, NOx and SO2 levels were higher in Patras than in Volos. The Patras’ harbor high traffic seems to drive the diurnal pattern of SO2 in that city.The examination of the rate of ozone accumulation, during the high O3 period (Apr.–Sep.), revealed the occurrence of two phases, a fast and a slow one, with different durations in each city. We suggest that the occurrence of such two phases’ patterns should be considered in relevant ozone studies.In both towns, the O3 levels were higher during weekends in comparison to midweek days, although NO levels were lower. Our results support the hypothesis that the weekend O3 effect is due to a combination of VOC sensitivity of the studied areas and the reduced NOx emissions during weekends. Based on the comparison of the weekend effect in the two cities, we suggest the occurrence of a feedback mechanism between peri-urban natural ecosystems (forests) and the polluting anthropogenic ones (cities).

Simulating effects of forest management on selected public forest goods and services: A case study

Silvicultural interventions alter forest characteristics such as stand structure, tree species composition and developmental stage. These forest characteristics in turn influence the quality and quantity of public goods and services a forest provides, such as space for recreation, clean water, and air purification. In this paper, we use a forest growth simulator and a geographical information system (GIS) to assess the effects of three silvicultural strategies on recreational suitability, water purification potential and air purification potential in a peri-urban catchment in Switzerland. For each of the three services, an index was developed to capture the suitability of a stand for providing the service. The growth simulator SILVA 2.2 was used to project forest development over 50 years under the three silvicultural strategies BU ‘business as usual’ (small patch cuts, Swiss selection system), NI ‘no intervention’, and MA ‘mass production’ (clearcuts and plantations of Picea abies). In all three strategies, road maintenance continued. The outputs of SILVA 2.2 were transferred into the GIS. Indices for the three services were calculated and aggregated over the study area. The development of the indices for all three services mainly reflected the changes in developmental stages and in the spatial patch distribution as a result of silvicultural interventions. No single strategy resulted in maximum values for all three indices. Recreational suitability was highest with the BU strategy and lowest with the MA strategy. The latter was due to the conversion of broad-leaved forests into plantations. Water purification potential was captured as nitrogen (N) storage in tree biomass and N removal by timber harvesting. In these nearly N-saturated forest ecosystems, the water purification potential was generally highest with the BU strategy, and lowest with the NI strategy. The air purification potential was higher with the NI than with the BU strategy. With the MA strategy, it rapidly decreased at the beginning, but increased after 30 years and surpassed the other strategies as soon as most of the plantations had reached the pole stage. The NI and MA strategies presented are clearly extreme strategies, which could not realistically be applied to the whole catchment as so many different owners are involved. However, the results of our study can be used to show to what extent management activities affect goods and services. We propose using such tools more often in forest planning processes to support the development of land-use visions and policies on a regional scale.

Institutional arrangements for articulating land and water management in peri-urban catchment: example of the metropolitan region of Sao Paulo, Brazil

The development of mega-cities exerts an increasing pressure on water resources in their peri-urban areas. Rapid changes in land use in these areas, characterised by the specific hydrologic functions they provide for the city, has resulted in increased pressures on water availability and quality. In the past, the traditional dual (urban/rural) focus of the institutions, their preference for sectorial legislation, and end-to-pipe technological responses have not been able to deal with these tensions in the metropolitan region of Sao Paulo, in the context of high social inequalities, uncoordinated metropolitan sectorial policies, and insufficient monitoring and control. New institutional arrangements based on democratic and territorial management of water resources are promoting a new vision on planning, and better integration on land and water management. Their efficient implementation may require a better definition of specific instruments to sustain economical compatible activities, facilitate metropolitan coordination and support the participation of the marginalised communities living on the edge of the city.

Articulating land and water dynamics with urbanization: an attempt to model natural resources management at the urban edge

In a rapidly urbanizing world, population densities no longer allow for unlimited access to safe water. Competition for water, often associated with competition for the access to land, tends to be exacerbated in peri-urban areas. The objective of this paper is to propose a multi-agent model prototype to represent the relationships between urbanization dynamics and land and water management in a peri-urban catchment area. A spatially explicit pilot model was developed using the Cormas platform. This prototype deals with a catchment that is the main drinking water reservoir and spring of a metropolitan area, and is subjected to high urban pressure and problems of pollution connected to land use and rain. The combined use of cellular automata, spatialized passive entities and communicating agents allows the articulation of the connections between hydrological processes (water cycle, pollution), land-use changes and urbanization. However, the representation is based on simplified dynamics and further work is needed to develop a simulation model that could be used as a discussion tool for land and water management at the urban edge.

Rainfall/runoff processes in a small peri‐urban catchment in the Andes mountains. The Rumihurcu Quebrada, Quito (Ecuador)

AbstractSituated at the foot of the Pichincha volcano, the city of Quito is frequently subjected to hydroclimatic hazards. In 1995 an 11·2 km2 watershed, located in the vicinity of the city, was equipped with eight rain gauges and two flow gauges to better understand the local rainfall/runoff transformation processes. Rainfall simulation experiments were carried out on more than 40 one‐square‐metre plots to measure infiltration point‐processes. The high density of measurement devices allowed us to identify the origin and nature of the various contributions to runoff for the different physiographic units of the watershed: urban area from an altitude of 2800 to 3200 m; farmland, pasture and forested land, and finally páramo above 3900 m. Runoff occurs mainly in the lower part of the basin and is caused by urbanization; however, the natural soils of this area can also produce Hortonian runoff, which is predominant in a few events. This contribution can be studied through rainfall simulation experiments. In the upper natural zone, the younger and more permeable soils generate less runoff on the slopes. However, almost permanently saturated contributing areas, which are located in the bottom of the quebradas, may generate flood events, the size of which depends on the extent of the area concerned. Variations in the runoff coefficients are related first to the baseflow and second to the amount of rainfall in the previous 24 h. This analysis, which underlines the complexity of a small, peri‐urban, volcanic catchment, is a necessary preliminary to runoff modelling in an area where very few experiments have been carried out on small catchments. Copyright © 2001 John Wiley & Sons, Ltd.

A situational analysis of the microbial water quality in a peri-urban catchment in South Africa

A situational analysis of a peri-urban catchment experiencing microbial water quality problems was carried out using data collected over two and a half years. The water and land use in the area was determined. The main sources of pollution were identified and the effects of dilution and bacterial die-off on water quality were evaluated by modelling the level of faecal coliforms along the length of the river using the QUAL2E model. As a result of the assessment, water quality goals were set for the catchment and suggestions were made for the improvement of microbial quality. Certain areas of the catchment are densely populated and both developed and informal settlements exist. Water is mainly used for domestic and recreational purposes. The river receives diffuse source discharges as well as point source discharges from four wastewater treatment plants and an industrial site. Assessment of indicator organism and pathogen analyses indicated that the main factors affecting the microbial quality were discharges from the sewage plants and runoff from informal settlement areas. The industrial activities in the catchment did not have a major effect. Modelling runs predicting faecal coliform levels demonstrated that bacterial die-off did not result in a significant improvement to the microbial water quality in the catchment.

A situational analysis of the microbial water quality in a pert-urban catchment in South Africa

A situational analysis of a peri-urban catchment experiencing microbial water quality problems was carried out using data collected over two and a half years. The water and land use in the area was determined. The main sources of pollution were identified and the effects of dilution and bacterial die-off on water quality were evaluated by modelling the level of faecal coliforms along the length of the river using the QUAL2E model. As a result of the assessment, water quality goals were Set for the catchment and suggestions were made for the improvement of microbial quality. Certain areas of the catchment are densely populated and both developed and informal settlements exist. Water is mainly used for domestic and recreational purposes. The river receives diffuse source discharges as well as point source discharges from four wastewater treatment plants and an industrial Site. Assessment of indicator organism and pathogen analyses indicated that the main factors affecting the microbial quality were discharges from the sewage plants and runoff from informal settlement areas. The industrial activities in the catchment did not have a major effect. Modelling runs predicting faecal coliform levels demonstrated that baclerial die-off did not result in a significant improvement to the microbial water quality in the calchment.