ARE RECHARGE-AREA MAPS USEFUL FOR LAND-USE PLANNING IN HUMID SETTINGS?

In recent years, many public planning agencies have begun including groundwater protection in local and regional land-use plans. The protection of “groundwater recharge areas” is often a component of such plans, and state agencies such as the Wisconsin Geological and Natural History Survey receive frequent requests for maps or spatial data depicting recharge areas. Well-intentioned planners and civic groups seek to use such maps as a basis for environmental protection through zoning, development of wellhead-protection areas or implementation of other land-use controls, and many hydrogeologists, including the authors of this paper, have advocated the importance of recharge-area protection. Unfortunately, in humid climates such as the Upper Midwest, recharge-area maps can be difficult to construct and conceptually misleading. These difficulties stem from at least eight characteristics of recharge having greater potential influence in humid areas. 1. Recharge can occur almost anywhere in the landscape. 2. Natural breaks in the continuum from low to high recharge rates are rare. 3. All recharge is important to the underlying groundwater system and adjacent surface-water features. 4. Recharge is a transient phenomenon, but maps represent steady-state information. 5. Anthropogenic features can alter recharge rates. 6. Accurate measurements of recharge over large areas are difficult to obtain. 7. Shallow aquifers most sensitive to recharge are rarely the main aquifers for water supply. 8. No standard or accepted scientific method exists for recharge area delineation. In southern Wisconsin we have estimated recharge rates and delineated recharge areas using various techniques, including water-balance modeling, baseflow and rainfall-runoff analyses, detailed field study, and inverse groundwater flow modeling. Each of these techniques produces useful results, but close agreement between the techniques is, not surprisingly, rare. Although these disagreements and inconsistencies are perfectly understandable to the scientists involved, they are not so easily understood or quietly accepted in the regulatory and planning world, where planners and the public desire well-defined and unchanging information as a basis for land-use decisions.