Arbejdsrapport fra Miljøstyrelsen, 17/2005 – Afslutning af ådalstypologi

Afslutning af ådalstypologi

Summary and conclusions

Background

This report summarizes the conclusions of a project covering development and testing of a typology for Groundwater/Surface water Interaction (GSI typology). The typology was developed for the purpose of evaluating river valley impact on water exchange and substance turnover at the transition zone between groundwater and surface water. The project has taken place from 2002-2004, and it has been publicized in Nilsson et al., 2003, and in Dahl et al., 2004.

Structure of GSI typology

GSI typology has a three-level structure: Landscape Type, River Valley Type and Flow Path Type. In the typology, groundwater flow is characterized on a gradually decreasing scale. Accordingly, Landscape Type characterizes the geological setting of the catchment area, governing the regional distribution of groundwater discharge to the valley. The River Valley Types characterize the interaction of the valleys with Adjacent Hydrogeological Units. Accordingly, River Valley Types describe groundwater discharge to the River Valley Aquifer base. Finally, Flow Path Types specify groundwater flow paths through the River Valley Aquifer to streams, giving way to evaluating denitrification capacity of the valley.

Objectives

This report presents the development of three tools for classification of River Valley Types and Flow Path Types:

GIS tool for geological profile construction, combining horizontal geological data from soil maps with vertical geological data from the national drilling database.
GIS tool for computation and generation of maps illustrating specific increase in median minimum stream flow.
Estimation method for mapping flow distribution in moraine landscape valleys.

Program of measures for surface water related to the Water Framework Directive

Within the Water Framework Directive, environmental objectives for groundwater should be outlined, and programs of measures for surface water prepared. Environmental objectives for groundwater will reflect its interaction and impact on chemical and ecological status of dependent surface waters (streams, lakes and coastal waters). Accordingly, the chemical and quantitative status of groundwater must not lead to failure in meeting environmental objectives of dependent surface waters, nor to significant damage to dependent terrestrial ecosystems (wetlands).

In preparing a program of measures for surface waters in the catchment area of nitrate endangered coastal waters, a tool is needed for delineating valley reaches receiving nitrate free groundwater, nitrate polluted groundwater, and reaches having high denitrification capacity. GSI typology is applicable for this purpose.

Tools developed for GSI typology will also support classification of groundwater bodies in accordance with the groundwater body typology (Miljøstyrelsen, 2004) recommended for basic analysis application in Denmark (WFD, Art. 5).

Restoration of wetlands related to the Danish Water Protection Plans II and III

Finally, GSI typology is applicable for restoring of wetlands related to the Danish Water Protection Plans II and III, in pursuing denitrification of nitrate at the transition zone between groundwater and surface water. Estimation of nitrate discharge in groundwater is made possible by use of tools developed within this project. The GSI typology may also offer practical guidance to flow distribution within the restored wetland in order to increase nitrate retention.