This document provides the information required by a user to apply the spreadsheet tool ZOOM_IGARF to run the groundwater flow model ZOOMQ3D and other associated utilities for the investigation of the impact of groundwater abstraction on river flows. This tool has\ud been developed to improve the techniques available to Environment Agency hydrogeologists involved in involved in assessing the impact of groundwater abstraction on river flows.The existing tools developed by the Agency as part of the Impacts of Groundwater Abstraction on River Flows (IGARF) project (NC/00/28) are adequate for up to about 50% of abstraction licence assessments. However, it is recognised by the developers that the existing IGARF analytical models do not produce results with sufficient confidence where:\ud • The particular hydrogeological setting significantly influences the impact of an abstraction and generic tools such as IGARF 1 are inadequate.\ud • The groundwater level falls below the bed of the river and away from hydraulic contact with the river.\ud • A more accurate spatial or seasonal distribution of the impacts on both flow and groundwater level is important, for example when the effects of several abstractions must be considered.\ud • There is a variation of hydraulic conductivity with depth as in most Chalk and limestone catchments.\ud • The regional context is important for estimating the local impact, which is often true for wetland sites.\ud Such features are represented in the many regional groundwater models that the EA has developed, however, these cannot be run quickly, i.e. within the time constraints of a licensing officer. The cost of developing a regional groundwater model, where one does not currently exist, is approximately £200k to £300k. Consequently, a tool is required to assess the impact of groundwater abstraction on river flow, which is relatively easy and quick to use but which incorporates some of the complex features that can be simulated by regional groundwater models. The Excel spreadsheet, ZOOM_IGARF has been developed for this purpose. This simple spreadsheet tool is used as pre and post-processor for the groundwaterflow model ZOOMQ3D with which a user can construct models including, for example,multiple dendritic river catchments. It is then possible to run the model and process the output to analyse the impact of an abstraction borehole on one or more reaches of a river within a catchment. The benefit of the use of Excel is that its application requires little prior knowledge of the structure of the input and output of the flow model, ZOOMQ3D
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