Page 9 - Yucaipa Sustainable Groundwater Management Agency - Yucaipa SGMA

5 | Groundwater Sustainability Plan for the Yucaipa Basin Area | San Bernardino Valley Municipal Water District
TASK 4.0 WATER BUDGET AND SUSTAINABILE YIELD
Seven subbasin boundaries within the Yucaipa Basin were defined by the USGS in 1970 based on groundwater
levels differences from data obtained from a limited set of wells. Previous workers have calculated the safe
yield of the sub-basins for water resource planning. The “safe yield” refers to the natural recharge available
to a groundwater basin. The term “sustainable yield” includes both natural and supplemental water sources
added to the groundwater system such as recharge of imported water and return flow from imported water.
In 2014, Geoscience was commissioned by Valley District and the GSA members to review the location of
subbasin boundaries and to provide an update of the sustainable yield for each subbasin and the basin as
a whole, and to determine the usable storage capacity for potential groundwater recharge. Since then, the
basin boundary has been modified by DWR at the request of basin stakeholders as a part of the SGMA
process resulting in an expanded basin boundary and adding an eighth subbasin. The newly constructed
USGS model will be used to update sustainable yield estimates for the Yucaipa Groundwater Basin and
subbasins. Our team will build on the 2014 safe yield report and use the USGS model to describe the water
budget and sustainable yield determinations.

TAC Meetings Deliverables: TM that will become the “Water
• Water Budget – Groundwater Inputs Budget and Sustainable Yield” chapter of the
• Water Budget – Groundwater Outputs Yucaipa GSP.
• Additional Recommended Meeting: Sustainable Yield

TASK 5.0 DEFINE MANGAGEMENT AREAS
The Yucaipa Basin boundary modification resulted in a different boundary than the boundary previous
studies have relied upon. The new Yucaipa Basin boundary extends into areas not previously associated
with the Yucaipa Basin including Live Oak Canyon to the southwest, and the Singleton area to the southeast.
The seven existing subbasins will be reevaluated and additional subbasins may be added if they are
determined to behave hydrologically different and may need to be managed separately. We will build on
our team’s understanding of the hydrogeology as well as specific management plans and needs by the
basin stakeholders to provide recommendations for the establishment of unique management areas. For the
purposes of this proposal, work up to this task will take place prior to Task 4 Water Budget and Sustainable
Yield. The proposed water budgets and sustainable yield will be computed for each management area and
will be assessed and provided as recommendations for discussions with the stakeholders.

TAC Meeting Deliverables: TM that will become the the “Management
• Additional Recommended Meeting: Areas” chapter of the Yucaipa GSP.
Define Management Area

ESTABLISH SUSTAINABILITY GOALS

TASK 6.0 DEFINE UNDESIREABLE RESULTS, MINIMUM THRESHOLDS, MEASUREABLE OBJECTIVES
The WSC-Geoscience team will work with the Yucaipa GSA and TAC to define the sustainability goal in
accordance with GSP regulations. The sustainability goal is critical and will define how groundwater will be
managed over the 20-year implementation phase and eliminate the undesirable results.

The definition of the undesirable results, minimum thresholds, and measurable objectives require scientific-
based methods and will be driven by technical information from the USGS model and information
documented in the Evaluate Supplies and Demands Phase (Tasks 1 through 5). The primary mechanism
for achieving consensus amongst the GSA members is driven through the stakeholder process in three
TAC meetings. During the stakeholder process of considering thresholds, the team will be cognizant of the
different management areas and representative monitoring required to measure the objectives. For the

Yucaipa Sustainable Groundwater Management Agency - August 9, 2018 - Page 9 of 208