Urban water management and planning in the context of integrated water resources management: Modau Case Study
Management and planning of urban drainage systems form part of integrated water resources management on basin scale. In this context the objectives of urban water management are extended. The concurring and conflictive demands pose a complex problem with interrelated objectives and impact relationships that have to be considered.
Current planning practice is not consistently structured. Often planning of measures takes place for separate sub-systems, e.g. urban drainage, and only considers single objectives disregarding the multiple dimension of the problem investigated. Planners and authorities tend to use standard solutions and exclude conceivable measures in an early stage of the planning process. Also, subjective assessment of sets of measures constrains finding optimum solutions. In fact, often a combination of different complementing coordinated measures provides the most efficient solution.
From a technical point of view the impact of mitigation measures can be analysed by means of computer based simulation models. Data processing tools assist in the preprocessing, interpreting and presentation of results.
Continuous stakeholder participation and multidisciplinary discussions facilitate the definition of management objectives in a more complete way, revealing common interests and synergy effects. However, involving the public into the planning process is often neglected.
The basic idea of the research project WSM300 is to provide a generic framework for coping with multi-objective management problems in catchments up to 300km². WSM300 is not a monolithic software application. On the one hand the method is based on close stakeholder participation. On the other hand it provides components for efficiently using available software tools, guiding and supporting the integrated planning process. The methodology encourages planners to structure the problem, systematically define objectives then develop scenarios and finally evaluate them.
A decision matrix is defined by management objectives and a set of measures. It represents a structured illustration of the decision space. It has been realised as a web-based shell application including database of measures, catalogue of indicators, etc. For engineering purposes the DSS comprises appropriate software components that support integrated modelling of system dynamics, data interpretation and evaluation. Besides these technical aspects WSM300 points out suitable methods to include stakeholders in the planning process. Three accompanying case studies exemplify the procedure. Experience from one case study will be discussed.
The Modau catchment area (244 km²) is situated in South-Hesse, Germany. It is characterised by intensive agricultural land use as well as high population density (up to 1250 inhab/km²). Pressures on water resources are considerably high resulting in impaired water quality and disturbances of flow regimes. Urban drainage systems represent a severe impact with nine WWTP and ninety CSOs along the river. The present problems in the Modau catchment are typical examples for intensively used small watersheds in central Europe.
The main objective of this case study is to identify and examine most critical impacts in detail. Effects of different measures are analysed and compared concerning their effectiveness to reach defined management objectives.
A watershed-advisory board consisting of representatives from forestry, fishery, hydro power production, water supply, industry, agriculture, nature conservation, communities and administration has been created. The advisory-board has met six times within the last two years and has significantly contributed to the discussion of management objectives and proposition of feasible measures. It also provides feedback concerning opportunities to implement the measures proposed.
Management objectives are: approximate natural hydrologic regime for minimum flow and peak flow of high frequency, conserve existing flood damage prevention level, reduce morphological deficits and remove disturbances of longitudinal continuum, improve biochemical water quality and preserve hydropower production of water mills.
Analysed sets of measures consist of several mitigation measures for urban drainage systems (decentralised infiltration, disconnection of unpaved areas from sewer system, extended use of sewer storage volume, biological sand filter), establish or extend riparian buffer strips, implement conserving agricultural land use practices and river corridor restoration measures.
A set of computer based simulation models is used for impact analysis concerning system dynamics, i.e. peak of sewer-overflow, dissolved oxygen concentration, etc. For the comparative evaluation of different scenarios a value benefit analysis is conducted. Benefit functions and weightings of different objectives have been discussed in the advisory board. The formalised multi criteria scheme allows the examination of sensitivities of weightings assigned to different objectives. Based on this information a well-founded discussion among the advisory board takes place.