7021

• UCREFRP Catalog Number: 7021
• Author: Oamek, G., et al.
• Title: Methodology For Analyzing Alternative Reservoir Shortage and Operating Criteria.
• USFW Year: n.d.
• USFW - Doc Type: \
• Copyright Material: YES

only annual deliveries from the reservoir to the M&I sector are transferred from the
Operations model to the M&I component.
Instream flow component
As,its name indicates the instream flow component estimates the benefits, and change in
benefits, of making reservoir releases to maintain flows in the watercourse. Instream
flow releases, if they are made at all, can be made for a number of reasons. Some
examples are maintenance of riparian and fish habitat, increased recreation
opportunities, and improved downstream water quality. Appropriate valuation
techniques will likely be different depending on the purpose of the instreamn releases.
Instream flow releases are considered in only one of the case studies examined here. In
this instance they are made for water quality purposes. The benefit of releases were
estimated as the avoided cost of water treatment. Similar to the M&I component,
annual deliveries from the Operations model are considered rather than monthly
deliveries.
CASE STUDIES
Two case studies demonstrate the modeling system. The first looks directly at
alternative operating criteria by examining a range of shortage triggers and shortage
criteria. The second focuses on the ability of the models to evaluate alternative
reservoir sizes for a given site.
It is important to note that the case studies are for illustration of the methodologies
and are not intended to accurately represent the actual situation in the study areas.
However, since a portion of the hydrologic and economic data come from actual Bureau
projects, the case studies carry the names of actual reservoirs.
Lake Cachuma California
Lake Cachuma is a multi-purpose reservoir located about 30 miles northwest of Santa
Barbara. Its annual average release of approximately 30,000 acre-feet is distributed to .
irrigation in the Santa Ynez valley (3,300 AF), irrigation along the Pacific South Coast
(13,300 AF), and municipal supply for Santa Barbara. No releases are made specifically
for maintenance of instream flows. This is an area of extremely tight water supplies,
whose geography prohibits economical importing of additional water supplies.
Groundwater is fully utilized. Pumping in excess of annual safe yield results in salt
water intrusion within a short period of time.
The Santa Ynez region is characterized by a ranching economy, where project water is
dedicated (in order of magnitude) to irrigated pasture, grass hay, alfalfa, barley, wheat,
dry beans, and tomatoes. Conversely, irrigation in the South Coast area concentrates on
high valued tree crops, such as avocados and lemons. The difference in types of
agriculture between these two sub-areas motivated a decision to consider separate -
shortage triggers and shortage criteria for each.
A 30 year period of record, using the flow years 1945-1974 were used to generate a
baseline series of monthly deliveries to the irrigation and M&I components. An extreme
drought during the late 1940's and early 50's resulted in 57 months of zero reservoir