UWM Plan - Municipal Water District of Orange County

Executive Summary
retail agency may choose to comply with SBx7-7 as an individual or as a region in
collaboration with other water suppliers. MWDOC and 26 of its member agencies as well
as the cities of Anaheim, Fullerton, and Santa Ana have created the Orange County
20x2020 Regional Alliance in an effort to help these agencies meet the water use
reduction targets required by SBx7-7. With a regional alliance, the entire region is able
to benefit from regional investments such as the Orange County Water District (OCWD)
and Orange County Sanitation District’s (OCSD) Groundwater Replenishment System
(GWRS), recycled water, and water use efficiency. Under this approach, MWDOC
estimates the interim regional target for Orange County would be 174.1 gallons per capita
per day (GPCD) in 2015 and the final target would be 156.5 GPCD in 2020.
This Plan also evaluates each source of water in the region. The resource mix for meeting
total demand includes local groundwater, recycled water, surface water, and imported
water from Metropolitan. The Plan documents MWDOC’s cooperative efforts with its
member agencies in developing local supplies. In fact, the region anticipates that the
percentage of its supply from each source will remain approximately the same for the
next 25 years, with 45% of its supplies from imported water and 55% of its supplies from
local sources in 2035, even with projected growth occurring.
Additionally, the Plan compares the region’s supply and demand to determine water
service reliability under different climatic conditions – types of water years. The Plan
first establishes the hydrologic conditions that define the types of water years in the
MWDOC region by considering a combination of the following three variables:
1. Total retail demand of the water year;
2. Local supply condition of the water year; and
3. Imported supply condition of the water year.
Imported-supply demand typically increases during dry years when the weather is hot and
there is a decrease in local runoff. Furthermore, in its Regional Urban Water
Management Plan (RUWMP), Metropolitan demonstrated it has developed flexible water
supplies through transfers and storage programs designed to increase its resources during
dry water year conditions. As a result, the water year is defined by the net difference of
total retail demand less local supplies. The greater the net difference, the more critical it
is for MWDOC to depend on imported supply. Using this approach, types of water years
in the region are defined as follows:
• Normal Water Year: average of 83 years, representing the historical hydrology
from 1922 to 2004;
• Single Dry Water Year: 1977 hydrology (yields the highest one year demand for
imported supply); and
• Multiple Dry Water Years: 1990 to 1992 (a sequence that yields the highest threeyear
demand for imported supply).
Municipal Water District of Orange County
2010 Regional Urban Water Management Plan
Final
E-3