There are many determinations of what constitutes the Native Safe Yield of a water basin, but a widely accepted definition is:
Safe yield means the annual quantity of water that can be taken from a source of supply over a period of years without depleting the source beyond its ability to be replenished naturally in "wet years".
Tehachapi has three basins in which the native safe yield has been determined for.
Tehachapi Basin: 5,500 acre-feet
Brite Basin: 500 acre-feet
Cummings Basin: 2,990 acre-feet
Safe Yield Total: 8,990 acre-feet
“Safe Yield” can be a moving target as we have weather patterns of wet and dry years that tend to paint a different picture year by year or even month by month during seasons of heavy groundwater use. The best way to determine the safe yield is to look at the basin’s groundwater level over a period of 5+ years and determine the trend.
All of the basins in Tehachapi are considered to be healthy. Tehachapi basin has prescribed water rights which are owned by individuals and entities such as the City of Tehachapi, the Golden Hills CSD, land developers, and businesses which need water for their daily operations.
Cummings Basin recently went through an Amended Adjudication in which the physical solution limited the water use across all parties in the basin by land size and type of use. While this Amendment was a good management tool, a consequence of this solution is that it severely limited the water available per acre for the existing farming operations in place. The amendment has now forced farmers to heavily depend on Imported Water that is brought into Tehachapi by the Tehachapi Cummings County Water District. In fact, farmers now need to get about 66-75% of their water from Imported Water and only about 25-33% from groundwater. The farmers dependence on Imported Water with very little flexibility to obtain additional groundwater now threatens farms more than ever in dry years as they depend heavily on a single source of Imported Water that is highly variable. If anyone took notice this year, the farmers in Cummings and Brite Basin cut back their plantings by about 33% due to a lack of imported water.
As time goes on, the model of having a high dependence on Imported Water is a horrible solution unless the user of the water has the ability to be extremely flexible. Groundwater and the Safe Yield of a basin is extremely dependable and this should be the model used to govern the development of homes and highly inelastic human use. When limiting the dependence of human needs to the water that is sustainable in an area then a community can guarantee itself to be water secure far into the future. Variable water such as Imported Water can then be used by farms and business ventures which have the ability to be flexible with what mother nature provides each year.
When farms use Imported Water then a portion of this water soaks into the ground and gets returned to the basin for safe use in later years. TCCWD has determined that this water that soaks in is 15% of the imported water used on a farm this quantity is called the “Return Flow”. The Return Flow water is then credited back to TCCWD and banked for future sales to M&I, other water uses, or even saved for use during drought years. This is a very symbiotic relationship as a portion of the water gets returned for a second use and we maintain a diversity of land use and open space around the community.
Remember. Safe Yield is safe growth.
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