A METHODOLOGY FOR BUILDING 3-D HYDROGEOLOGIC FRAMEWORK MODELS IN AREAS OF SPARSE DATA WITH A CASE STUDY IN NORTHWEST KENYA

Computer-based three-dimensional hydrogeologic framework models (HFMs) are constructed from geospatially registered surface and subsurface geologic data. The information presented in an HFM includes interpretations of the lithologic well logs and cross sections, geophysical interpretations, and isopach data for hydrogeologic units. Limitations in HFMs exist because of the difficulties representing the complex geometry and spatial variability of heterogeneous hydrogeologic materials and geologic structures.

In some regions, particularly in developing countries, hydrogeologic studies may be hampered by sparse and/or poor-quality data. A workflow was developed utilizing experience in building HFMs for developing areas in the world that lack sufficient quality data. Accommodating these data limitations requires professional experience, judgement, and an acknowledgement of how inherent uncertainty will impact the resulting models and interpretations. Cross sections from various sources can be used or created, and data (if available) from proprietary databases (for example, lithologic logs as well as geophysical logs from the petroleum industry) could be utilized to inform deeper aspects of a hydrogeologic system. Much of the interpretation of the hydrogeology relies on tacit and expert knowledge of the geology that is supported and shared by local geoscientists. This type of knowledge is most easily realized in the construction, use, and reliance on interpretive cross sections that incorporate “hard” data such as stratigraphic contacts, as well as “soft” data such as the geoscientists’ experience and expert knowledge on the local geology.

A case study of an HFM from northwest Kenya, covering approximately 145,000 square kilometers, is presented. The construction of the HFM used only 67 of nearly 4,000 well logs from shallow water-supply wells that had useful lithologic data and were properly located. Other data included cross sections, mapped lithology, and topographic data. The HFM is used to assess drilling locations and availability of groundwater resources for water-supply wells as part of United States Agency for International Development funded water security efforts in East Africa.