WSP09325 - Laserfiche WebLink

Home Browse Search

Question: Will the Closed Basin Project turn San Luis Valley into a dust bowl? ,0 Answer: No, the operation of the Closed Basin Project will not turn the Valley into a dust bowl. The fears which many people have expressed on this subject are based on mis- understanding. This misunderstanding focuses on two official statements about the project. These official statements are: (1) "the Project will salvage water now being lost to evapotranspiration. . . . . . ," and (2) "decreased plant vigor may result (from the operation of the project) in some areas . " Some people have interpreted these statements to mean that operation of the project will result in the loss of existing vegetation from a vast part of the valley. That is not what the statements say, and it is not reasonable to believe this will happen. In the Closed Basin sump area, the water table is generally 2 to 6 feet below the surface. A large amount of water evaporates from the project area every year. Project facilities are designed to salvage some (not all) of this evapo- . rated water by lowering the water table in the Closed Basin sump area (only within the project boOndary). A lower water table will reduce the amount of water transferred from the soil surface and from some of the vegetation to the atmosphere. " Water is transferred to the atmosphere from leaves of growing plants (trans- piration) and from the soil surface (evaporation) by a process called evapo- transpiration. Plants in the San Luis Valley and the area of the Closed Basin (not including wetlands) are well adapted to low rainfall and moisture levels; however, they can and do use large amounts of water when it is available. The efficiency with which a plant uses soil moisture often decreases with too much available water. A point can often be reached where high moisture levels reduce plant growth and survival. Where there are always very high water tables, the rate of plant growth will likely be less than if the water table and available water were lower. Lowering high water tables within project boundaries will not automatically result in the death of all existing vegetation. Some plants will be adversely affected by lowering water tables. Others will be helped and increased plant growth will occur. Evaporation of soil moisture can be very high when water levels are near or at the soil surface. The evaporation rate from a wet soil surface generally exceeds that transpired by plants under the same climate conditions. Reducing water levels@{H:.8\..1 decrease total water lost from the soil surface and will often maintain greater plant growth rates. Both upland and wetland vegetation in the San Luis Valley and the Closed Basin have been studied for many years. A 3-year growth study was conducted by the Bureau of Reclamation on basically upland vegetation. The study area was located where the water table was lowered by a pilot salvage well. The study has shown that shrubs right around project salvage wells will be adversely affected. Most of the shrubs within several hundred feet of the well will be smaller in size and fewer in number after several years of project operation. Younger shrubs will most likely survive even near the wells. These shrubs have the ability to follow the water table down as they continue to utilize surface precipitation. Older shrubs" do not respond to rainfall as well. The reaction of saltgrass and wiregrass to a lowering more complicated. Where the water table is more than depend'on direct rain and snowfall for annual growth. water table is a little 5 feet down, most grasses In these areas, project