Page 45 - Beaumont Basin Watermaster

Beaumont Basin Watermaster
2013 Reevaluation of the Beaumont Basin Safe Yield 3-Apr-15

Beaumont Basin resulted in reduced subsurface groundwater outflow out of the basin (see
Table 7 and Figure 38). Increased return flow and the capture of groundwater that would have
otherwise left the basin resulted in a higher Safe Yield.

In the late 1990s and 2000s, a combination of factors began influencing the water balance and
the Safe Yield. Increased pumping by the City of Banning in the southeast portion of the
Beaumont Basin and immediately outside the basin depressed groundwater levels in this area and
increased the rate of subsurface outflow. Starting in 2006, the relationship between groundwater
pumping and Safe Yield was further complicated by the introduction of artificial recharge. The
resulting water balance of the Beaumont Basin indicates a moderate increase in Safe Yield
between 2000 and 2012 (5,123 acre-ft in 2000 to 5,881 acre-ft in 2012).

6.2 Safe Yield Based on Future Projections of Land Use and Basin

Management
The Safe Yield of the Beaumont Basin changes with changing land use, groundwater pumping
and artificial recharge. In keeping with the methodology for estimating Safe Yield, as expressed
in Equation 4 above, land use conditions must be representative of the time period for which the
Safe Yield applies. Given the significant changes in land use in the Beaumont area since 2000, a
Safe Yield estimated based on historical data would not be as representative as a Safe Yield
estimated based on current or future land use projections. Furthermore, groundwater pumping
has also increased significantly in the period between 2000 and 2012. Groundwater pumping
can increase the Safe Yield, within limits, because it results in the capture of groundwater that
would have otherwise migrated out of the basin. Given that the current levels of groundwater
production are projected to remain the same or increase, a forward projecting Safe Yield estimate
that takes into account the higher groundwater pumping rates would be more representative than
a Safe Yield estimate based on historical data.

The calibrated groundwater flow model was used to estimate the Safe Yield of the Beaumont
Basin based on a 10-yr future projection (2013 through 2022) of groundwater pumping and
artificial recharge. The analysis included development and analysis of a production and artificial
recharge scenario developed based on the findings from the historical water balance and the
premise that changes in groundwater production and artificial recharge influence the Safe Yield.
It is noted that although the Safe Yield is based on the first 10 years of the future projection
scenario, the total term of the model projection was 20-yrs (2013 through 2032).

The following assumptions in the water budget were applied to the future projection scenario:

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