Summary

Description

The calculations in this report are to determine average surface water requirements are for planning purposes and are not intended to represent actual Lahontan Valley wetlands management plans or practices. These calculations were developed to serve as a conceptual evaluation of a possible water budget for Great Basin wetland habitat in Lahontan Valley. The 5.1 acftacyear average does not take into account the full range of wetland management options necessary to sustain productive wetland habitat over a long period of time under varying hydrologic conditions e.g. drought and flooding. Additionally, wetland management must include provisions to restore and maintain natural biodiversity, mitigate drainwater quality problems, prevent avian disease outbreaks, or flush accumulations of salts and trace elements that occur in these terminal wetlands. The average surface water requirement calculated above does not provide any surface water to mitigate avian disease control or to flush perennial and to a lesser extent ephemeral emergent wetland habitats of accumulated salts and trace elements. This would require additional surface inflows that are not reflected in the 5.1 acftacyear surface inflow average calculated to offset only evaporative, evapotranspiration, and seepage losses. Surface water requirements for Lahontan Valley wetlands would also change based on the desired mix of wetland habitats. For example, if emphasis was placed on providing a greater percentage of ephemeral playa wetlands the average surface water demand would be lower e.g., 50 percent playa, 30 percent emergent, 20 percent perennial, the average surface water requirement would be about 4.5 acftacyear. On the other hand, if the management emphasis was to provide a greater percentage of ephemeral emergent and perennial wetlands with little ephemeral playa the average surface water demand would be greater e.g., 10 percent playa, 40 percent emergent, 50 percent perennial, the average surface water demand would be about 6 acftacyear. For the purposes of determining a representative wetland water demand for management planning relative to the Lahontan Valley Wetland Water Rights Acquisition program proposed by the U.S. Fish and Wildlife Service, it is reasonable to use a figure of 5 acftacyear as an annual average to calculate surface water requirements. This recognizes that more comprehensive wetland management planning may increase or decrease the average surface water requirements for Lahontan Valley wetlands.