A WATERSHED-SYSTEM CHARACTERISTICS APPROACH TO MAPPING GROUND WATER RESOURCES

An approach to estimate the renewable ground water resources (recharge/discharge) is based on system analysis. The analytical procedure, used as a research tool, is to study the stream runoff components (annual, seasonal and monthly minimal) and includes three phases: (1) system analysis of the geosphere, i.e. Earth landscape systems in three-dimensional fashion, (2) ground-water flow field classification and hierarchical subdivision and (3) spatial-temporal mapping of stream runoff. The fundamental premise of the system analysis is the consideration that the hydrosphere system pattern can be recognized at four levels (planetary, global, regional, basin). The investigation proceeds from a global to a regional or basin level to a local level, with the greater detail available at the lower levels adding refinement to the description of the hydrologic landscapes and hydrogeological units.

In Minnesota, the methodology was applied in four stages. First, the temporal-spatial variability of global stream runoff was quantified and its pattern was identified, then the spatio-temporal structure of stream runoff as well as recharge/discharge rates were estimated for the entire state. After that, the recharge rates were quantified for east-central Minnesota, where rigorous quantitative analysis was done. Finally, for the Twin Cities Metropolitan area (TCMA) the values were derived from results in east-central Minnesota, based on empirical pattern analogy, and the minimal annual ground-water recharge map for TCMA was compiled at a scale 1:200 000 (available at MGS FTP site).

The methodology presented here allows not only to produce ground-water resources maps at many scales and levels, but also they could be aggregated with other types of physical, economic, social and environmental data to help shed light on overall changing conditions of water availability, use, and competition.