Upper Klamath Basin Groundwater Studies Active

Overview of the Groundwater Hydrology of the Upper Klamath Basin

The upper Klamath Basin has a substantial regional groundwater flow system. The volcanic rocks that underlie the region are generally permeable and compose a system of interconnected aquifers. Interbedded with the volcanic rocks are sedimentary rocks composed of fine-grained lake sediments and basin-filling deposits. These sedimentary deposits have low permeability, are not good aquifers, and probably reduce groundwater movement in some areas. The regional groundwater system is underlain and bounded on the east and west by older volcanic and sedimentary rocks that have generally low permeability.

Overview of the Regional Groundwater Model

The U.S. Geological Survey MODFLOW model simulations show that the timing and location of the effects of groundwater pumping vary markedly depending on pumping location. Pumping from wells close to groundwater discharge features, such as springs, drains, and certain streams, can affect those features within weeks or months of the onset of pumping, and the impacts can be essentially fully manifested in several years. Simulations indicate that seasonal variations in pumping rates are buffered by the groundwater system, and peak impacts are closer to mean annual pumping rates than to instantaneous rates. Thus, pumping effects are, to a large degree, spread out over the entire year. When pumping locations are distant from discharge features, the effects take many years or decades to fully impact those features, and much of the pumped water comes from groundwater storage over a broad geographic area even after two decades. Moreover, because the effects are spread out over a broad area, the impacts to individual features are much smaller than in the case of nearby pumping.

Overview of Groundwater Management Modeling Efforts

A groundwater management model was developed to identify optimal strategies to meet water-user needs while not violating defined constraints on impacts to groundwater levels and streamflows. The overall goal of the modeling effort was to determine the patterns and rates of groundwater pumping that meet the supplemental groundwater demands of the Klamath Reclamation Project. To ensure that groundwater development does not adversely affect groundwater and surface-water resources, the groundwater-management model includes constraints to withdrawal and drawdown. The model indicates that supplemental groundwater pumping can be managed to avoid adverse effects to groundwater discharge that supports critical aquatic habitat.