In an average year, Columbia County receives about 33 inches of rain and snow. Of that, about 8 inches recharges the water table. In a very wet year, when the county may receive as much as 50 inches of precipitation, the estimated average recharge rate is about 14 inches per year. During very dry years, when precipitation can be as low as 23 inches, average recharge may be as low as 1.5 inches.
The slope of the water table determines the direction of groundwater flow. Groundwater is always moving, generally very slowly, through the saturated zone. Like water on the land surface, groundwater moves from areas of higher elevation to areas of lower elevation, eventually discharging in lakes and streams.
Iowa County contains over 400 springs, and it is likely that more springs exist than are shown on the map on the reverse. Spring flows in the county range from seasonal seepages to perennial flows of over 450 gallons per minute (gpm), but most spring flows are less than 100 gpm. Springs are found in stream valleys across the county except in the far north near the broad floodplain of the Wisconsin River. Some springs form the headwaters of streams, whereas others discharge directly into a stream channel or flow into wetlands and low-lying areas at the base of a valley.
Most of Iowa County’s groundwater is moderately to highly susceptible to contamination. Compared to the most susceptible areas, these regions have lower recharge, a greater depth to the water table, and bedrock with few fractures. Areas mapped as least susceptible to contamination are primarily wetlands adjacent to streams and rivers. Wetland soil limits infiltration, and these are areas where groundwater discharges to nearby surface water. Although contamination can reach the water table in this setting, extensive groundwater contamination is unlikely.
Groundwater is water contained underground in pore spaces and fractures in sediment and rock. The water table is the undulating surface of the saturated zone; pore spaces and fractures are completely filled with water below this surface. The water table is an important feature of the groundwater system because its slope determines the direction of groundwater flow and where groundwater contributes to the flow in springs, streams, and rivers.
This report describes a division of the state, geographically, into nine major groundwater units-hydrogeologic districts; the concept being that within each district, ground-water occurrence is somewhat uniform. A division of the state into these hydrogeologic districts will define areas with natural hydrogeologic boundaries as potential management units and will provide a basis for the transfer of hydrogeologic knowledge within these units. It will also help to enhance the public's understanding of ground water in Wisconsin. This division by district represents one level of detail. The districts can be grouped into larger, more general units (provinces) or subdivided into smaller, more detailed units (subdistricts or zones), as needed for research, planning, or management purposes (Zaporozec, 1972). They are named districts to differentiate them from the nationwide hydrogeologic provinces.
Washington‘s complex geology gives rise to many geologic hazards—earthquakes, active volcanoes, landslides, tsunamis, and abandoned mines. One of the more important missions of the Division of Geology and Earth Resources is to reduce the impact of geologic hazards on the citizens of Washington. As Washington’s geological survey, the Division contributes to the safety and economic well-being of Washington’s citizens by educating the public, government, and industry about the consequences of foreseeable geologic events and the nature of the land around us, including the availability of important resources such as aquifers and sand and gravel. The Division has provided this information at very low cost to taxpayers, and studies have shown that providing geologic information to the public more than pays for itself over time. The Division of Geology is regarded as the primary source of geological products and services in support of decision-making by Washington’s government agencies, its businesses, and the public.
Recognizing the value and importance of physical and digital geology-related resources, the Utah Geological Survey (UGS) in partnership with the U.S. Geological Survey (USGS) started a Geologic Data Preservation Project in 2007, to collect, inventory, preserve, and manage geologic data of value for future use by industry, government, academia, and the public. These data are an important resource for those involved with land-use planning and management; geologic, geotechnical, and environmental investigations; mineral and resource exploration; real estate due-diligence activities; environmental protection; academic research; and teaching.
Landslides are one of the most costly natural hazards in the United States, threatening every state. A recent estimate by the U.S. Geological Survey (USGS) states that 25 to 50 deaths and damage exceeding $2 billion occur every year in the U.S. (Spiker and Gori, 2000).
Losses from landsliding in Oregon range from $10M to hundreds of millions a year, making landslides one of the most common and destructive natural hazards in the state. DOGAMI uses lidar, a technology that uses laser light, to create very accurate landslide inventory maps for Oregon.