Geophysical Investigations For Groundwater In The Lower Klamath Lake Basin, Oregon

The Klamath Basin was in the national news regularly during the summer drought of 2001 when the Bureau of Reclamation severely curtailed distribution of irrigation water for agricultural use. The Lower Klamath Lake basin is a classic graben structure on the western edge of the Klamath Basin, at the north-west margin of the Basin and Range province. Historically the regional agriculture has relied completely on surface water from Upper Klamath Lake and the Lost River. Groundwater production of the quantities necessary for agricultural use typically comes from fractured basement volcanic rocks and fault zones. The highly political nature of the situation led to a shot-gun approach to groundwater exploration. An extensive drilling program was initiated in California and a more restricted program in Oregon. Geophysical exploration programs including CSAMT, ground magnetics, gravity, and seismic reflection, were contracted by several agencies and conducted by several different geophysical contractors. Presented here are the results of a 200 station gravity survey conducted in the northern section of the Lower Klamath Lake basin. Those results are integrated with results from other geophysical programs. In the future it is hoped that drilling of 6” exploratory wells will further refine the geophysical interpretations. Geophysical tools have proved effective for groundwater exploration in the Klamath Basin. In the Lower Klamath Lake basin geophysical results indicate a more complex geology than anticipated with multiple volcanic units interbeded with the sedimentary units within the basin.