Freiburger Schriften zur Hydrologie

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Band/volume 21: EISELE M. & LEIBUNDGUT Ch. (2006):

Hydrologische Güte - ein Beitrag zur erweiterten Bewertung von Flusseinzugsgebieten im Gewässerschutz

The assessment procedure "Hydrological Quality" enables the assessment of human impacts on the hydrological system of river basins. Substantial parts of the methodology have been developed in a project, funded by the state of Baden-Württemberg (research program BW-PLUS) and completed in 2001. The aim of a subsequent project, also funded by BW-PLUS, was the development of a procedure, which is operationally applicable at regional scales and state wide. To demonstrate its applicability, the procedure was applied to the state of Baden-Württemberg. As part of the procedure a software system for operational application (AHQ-IHF) was developed on the basis of test applications.
In the assessment part catchment properties the potential human impact on the hydrological system is quantified based on spatial data which are commonly available. As an aggregation of the different assessment parameters the "index of human impact" is calculated. In the part stream flow dynamics anthropogenic alterations of the annual variations of different stream flow variables are identified and assessed. To describe the temporal variability of stream flow the Indicators of Hydrological Alteration (IHA) are chosen. They describe different aspects of the hydrological regime and can be linked to specific ecological functions. The human impact is investigated using measured or modeled time series of daily stream flow. Alterations in the annual time series of the different stream flow variables are quantified using the Range of Variability Approach (RVA). Nutrient emissions (nitrogen and phosphorus) in the river basins and the water quality of rivers (concerning nitrogen and phosphate) are subject of the optional assessment part nutrient budget and water quality. Nutrient balance models (e.g. MONERIS) are used for quantification of the emissions. The assessment of water quality is based mainly on time series of water quality samples.
The software system AHQ-IHF (Assessment of Hydrological Quality) enables an operational application of most of the calculations involved in the methodology. Within the system differ-ent projects (e.g. a set or subset of catchments) as well as different project versions (e.g. dif-ferent datasets or calculation settings) can be managed. For defined lists of investigation areas (e.g. catchments) or gauging stations spatial data (point-, linear and areal data) as well as time series can be imported, processed and assessed. Import and export of data, calculation and classification steps are activated through a graphical user interface. Data are managed in a database (MS-Access) using a specific data model.
As a result of the application of the procedure assessment data for catchment properties as well as for nutrient emissions and water quality are available for the entire state of Baden-Württemberg. An assessment of alterations in stream flow dynamics was carried out for 79 gauging stations. In addition a map of resulting flow alterations in the river system was pro-duced, combining the results of the gauging station based investigations with results from the morphological survey. This map (status: 09/2005) is provided in the appendix of this report. It will also be published in the 3rd delivery of the "Water and Soil Atlas Baden-Württemberg" in 2006/2007.
Applying the procedure in Baden-Württemberg anthropogenic impacts on water balance and nutrient budgets could be shown mainly in the Neckar basin, the Rhine valley and in parts of the Danube basin. Anthropogenic impacts on stream flow dynamics are only small or moder-ate in most rivers of Baden-Württemberg. More severe impacts in some rivers can be ascribed to the effect of dams or discharge abstractions.
With the completion of the subsequent project in 2004 an operational assessment procedure is now available. The advanced procedure was developed as a tool for water recource planning at the survey scale. It can be used for assessing the anthropogenic impacts on hydrology and water quality of river basins in addition to the regular biological and morphological assess-ment of rivers. The proposed assessment of impacts on the variability of stream flow focuses on an aspect of river ecology widely ignored so far which is an important factor for aquatic habitats.
Volume 18 of the paper series "Freiburger Schriften zur Hydrologie" focused mainly on the methodology for the assessment of nutrient budget and water quality as well as on the results from the application of the procedure in different test catchments. The final document presented now as volume 21 in the same series contains the revised methodology of all three parts of the methodology (with a special focus on the part stream flow dynamics) as well as the results which were obtained in the subsequent project.