In integrated river basin management, measures for
reaching the environmental objectives can be evaluated at different scales,
and according to multiple criteria of different nature (e.g. ecological,
economic, social). Decision makers, including responsible authorities and
stakeholders, follow different interests regarding criteria and scales. With
a bottom up approach, the multi criteria assessment could produce a
different outcome than with a top down approach. The first assigns more
power to the local community, which is a common principle of IWRM. On the
other hand, the development of an overall catchment strategy could
potentially make use of synergetic effects of the measures, which fulfils
the cost efficiency requirement at the basin scale but compromises local
interests. Within a joint research project for the 5500 km
The Werra river basin is situated in central Germany within the upper part of the Weser catchment. Before German re-unification it was divided by the inner-German borderline. The main industry in the catchment is potash mining, associated with a high salt load of the Werra River. Like for many German rivers, the morphological conditions of the river courses and the ecological continuity were affected before implementation of the European Water Framework Directive (WFD). Agricultural land use dominates in the North-Eastern area of the catchment. In former Eastern Germany many dispersed settlements were not connected to the public sewer system and were often not equipped with decentralized wastewater treatment. While the degree of connection was 98 % in Hessen, it was 48 % in the Thuringian part of the Werra catchment in 2001. As a consequence, the nutrient load of the catchment was high compared to the relatively extensive land use and the low population density. The ecological community was degraded in several water bodies, showing a good ecological status according to the AQEM assessment system (Hering et al., 2004) only in upstream regions of the Thuringian Forest.
For the implementation of the WFD, an exemplary river basin management plan (RBMP) was elaborated by an interdisciplinary research team, supported by local water authorities (Dietrich and Schumann, 2006). The RBMP provided several alternative strategies for the catchment, which were prepared for a final decision procedure supported by a multi criteria decision support system (Dietrich et al., 2007). Within this paper we focus on spatial aspects of measures for the improvement of the hydro-morphological conditions and the reduction of nutrient loads from point sources and diffuse sources (for a detailed description see Dietrich and Funke, 2009).
One of the challenges in spatial decision analysis is the spatial aggregation of criteria. For an RBMP, measures are located throughout the catchment area. The criteria for the individual measures can be aggregated in space to get an overall multi-criteria assessment of alternative combinations for the RBMP. This technique was applied in the widely used MULINO-DSS (Giupponi et al., 2002). Alternatively the multi-criteria analysis (MCA) can be applied for each of the locations separately, and then the outcome of the MCA is aggregated in space. Both pathways of aggregation of criteria and space can lead to different overall results (Herwijnen and Rietveld, 1999). The first path better represents the characteristics of the basin, whereas the second path allows different preference structures for the smaller sub-units, hence better represents the local situation. By aggregating criteria, positive and negative effects can be smoothened, with the consequence of reduced distinctive character of the alternatives. This kind of spatial compensation can be addressed by introducing additional criteria as Nijssen and Schumann (2014) showed for flood risk management. In this study, we present a strategic combination approach, which includes a criterion for social acceptance of the measures in order to represent the stakeholders' preference for the local measures.
The ecological assessment with AQEM showed significant deviations from the species composition, which could be expected for the types of water bodies in that catchment. The salt load of the lower Werra River was not subject of the investigations even if it was known that it is one of the causes of ecological degradation for the affected water bodies. Apart from this, morphological deficits in most river courses (Fig. 1) were identified as a major problem to address in river basin management (Dietrich and Schumann, 2006), hence in the implementation of the Water Framework Directive. The morphological deficits include the riparian and river bed structure, but also numerous structures from groundsills to reservoir dams which disturb or prevent fish migration. Also the overall saprobial state (Fig. 1), as well as nitrate and phosphorus concentrations were found to be beyond the levels which support a good ecological state according to the WFD. The quantitative investigation of the nutrient cycle was done with a chain of models, combining an agricultural production model to compute nutrient losses from agricultural areas, a point source emission model for sewage treatment, and a coupled SWAT-RWQM1 model to simulate nutrient turnover and transport at catchment scale. The emissions of nitrogen and phosphorus from point and non-point sources show an uneven distribution over the catchment, closely related with urban land use in the case of point sources (Fig. 2) and agricultural land use in the case of diffuse (non-point) sources (Fig. 3).
Significant morphological alterations (left) and significant saprobial load (right), indicating priority areas for measures (changed from Dietrich and Schumann, 2006).
The objective of river basin management according to the WFD is to reach a
good ecological state of all water bodies by 2015, with some possible
exemptions e.g. for heavily modified water bodies or due to long lasting
sanitation or disproportionate costs. The WFD gives a framework for the
development and 6-yearly update of river basin management plans (RBMP). The
RBMP collects all measures, which were decided by the respective bodies.
Within the Werra project, an exemplary RBMP was developed to address the
environmental issues of the catchment that were introduced in Sect. 2.1. Different
from the formal and final WFD RBMP, in this paper we provide alternative
solutions for the selection phase of the decision process, which means that
we present not a single solution but alternative measures, which follow the
same overall objective. The following types of measures were considered and
then designed for the water bodies in order to fulfil the objectives of the
WFD:
Improvement of the morphological conditions of the river Ecological continuity by removing barriers or building fish passes Creation of riparian buffer strips Plantation of natural woods along the rivers Removing bank reinforcement Removing of canalization Reduction of nutrient pollution from diffuse sources
Conversion of arable land to permanent grassland Reduction of fertilizer use Optimization of crop rotation Reduction of nutrient pollution from point sources
Connect dispersed settlements to sewage system New stage of expansion of treatment plants Increase capacity of sewage treatment plants Construct new sewage treatment plants
Nitrogen emissions (left) and Phosphorus emissions (right) from point sources, indicating priority areas for measures (changed from Dietrich and Schumann, 2006).
All measures were evaluated with the following methods and criteria (Dietrich and Schumann, 2006):
Nitrogen emissions (left) and Phosphorus emissions (right) from diffuse sources, indicating priority areas for measures (changed from Dietrich and Schumann, 2006).
Priority areas for actions within the two strategies focussing on polluter pays principle (ST3, left) and cost-efficiency (ST4, right). PT is the total sewage plant capacity of population equivalent (changed from Dietrich and Schumann, 2006, ST1 and ST2 are shown in Dietrich and Funke, 2009).
Categories and scales of the ecological benefit criterion (changed from Dietrich and Schumann, 2006).
The final result of the project's planning are several alternative combinations of measures for the RBMP, which can be used as a decision matrix for multi-criteria evaluation and computation of a ranking based on preferences for the different criteria. This final matrix is computed for the entire Werra catchment. The aggregation of criteria from locations (single measures) via water bodies and their contributing catchments up to the catchment scale was complex and hat to be treated differently for the different criteria. For that reason, the pathway of aggregating criteria first was not possible. We decided to build combinations of measures according to different principles of strategic planning and policy making. Thus we called the final alternatives “strategies”.
The aggregation of the criteria introduced in Sect. 2.3 faced the following issues:
Four catchment management strategies and respective decision criteria (from Dietrich and Funke, 2009; Dietrich and Schumann, 2006).
The complexity of the problem does not allow a spatial multi-criteria aggregation at smaller scales than the overall catchment. Otherwise, much more detailed studies had to be performed regarding the ecological benefit and the social criteria. Furthermore, a decomposition of the upstream – downstream effects of nutrient reduction had to be done. As a consequence, we performed a coordinated catchment strategy development. This follows the following principles:
All the four basic strategies were computed and all criterion values were calculated with the respective methods. For the ecological benefit, the willingness to pay for biodiversity was calculated with a declining value. The measures for ecological continuity prefer the removal of structures where possible. Table 2 shows the results of the overall assessment.
The polluter oriented strategy ST3 does not only show the highest costs, but also the highest conflict potential because farmers expressed negative about the planned measures (Table 2). The optimized strategy ST4 is marginally cheaper than ST1, but shows better ecological benefit due to high valued riparian buffers. But, ecologists estimated that 13 instead of 10 resp. 11 water bodies need extended monitoring due to a marginal fulfilment of the ecological objectives, which (under uncertainty) can lead to the need for additional measures.
The results of the simulation and aggregation of criteria highlight problems in following the “polluter pays” principle and the WFD requirement of overall “cost efficiency of the program of measures” for the RBMP at the same time. A decomposition of larger scale measures and the redistribution of costs for measures with basin wide effects could be done by concepts like emission trading for nutrients. Then, the cost recovery happens at the polluters, but the spatial aggregation effects of nutrient reduction can be utilized in the best way.
Further work will be done in comparing different aggregation methods and different MCA methods. For very large basins, the study could be designed differently – e.g. the Werra basin is one part of the Weser basin, and the Fulda basin and the middle Weser and lower Weser sub-basins could be assessed separately. Then, the four larger parts of the whole basin could be aggregated in both ways (first space or first criteria).
This work is based on results of the joint research project “River Basin Management of the Werra River” (principal investigator: Andreas Schumann, Bochum). The German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung, BMBF, FKZ 0330211) is acknowledged for funding of the project and the book publication of the results. We would like to thank all those involved in the original project for their collaborative efforts and for sharing data, knowledge and results.