Bulletin Board

Conjunctive Water Management

Full use of existing stored water supplies and aqueduct capacities ensure the efficient delivery of water within Salt Lake County

August 1, 2000

Introduction

Water supply deliveries within Salt Lake County are complex. There are over 20 different water entities, serving nearly one million people over a 764 square mile area..  Moreover, the sources of supply and climate are factors in the delivery of water.  The arid climate creates a double whammy; scarce water supply and high water usage. The Salt Lake valley floor receives about 16-inches of precipitation, not enough to sustain crops and greenery without efficient irrigation. Water short years are common, exacerbating the already difficult task of developing and delivering water to the growing metropolitan area of Salt Lake County. Storage projects store snowmelt run-off in the spring for use during the summer months. Large aqueducts convey the water supply to residents in Salt Lake County.

Typical Utah hydrograph. Water from snowmelt is stored in reservoirs during the spring and used during the summer peak demand.

Water was foremost in the minds of early leaders, recognizing that without water the full potential of the Salt Lake valley was limited.  This continues today; however instead of water for crops, it's water for people and modern urban needs. Today about one-half of the water delivered is used for outside irrigation of urban lawns and gardens.Water conservation is being urged to reduce the amount of water needed in the future and to reduce the summer demand on treatment and conveyance systems.

According to the Utah Division of Water Resources, in 1995 331,500 acre-feet of water was used for Municipal & Industrial (M&I) use within the Jordan River Basin. Without conservation, this is expected to increase to 496,500 acre-feet by 2020.

Water distribution requires a network of storage reservoirs, aqueducts, treatment plants, thousands of miles of distribution mains, distribution reservoirs and pumping plants. Each of the water entities is separated into individual networks; however there are some interconnections and common facilities that are used on a regular basis or during emergencies. It is estimated that over 500 million gallons of water is delivered within Salt Lake County during a summer day. This is equal to draining all the water in Mt. Dell Reservoir in 2 days.

Surface water is treated in 7 water treatment plants. Deep wells are scattered throughout the valley to meet local water demand and to maintain pressure within the distribution systems.

Water Storage Projects

Water stored in reservoirs provide drinking water supply during the summer.

Because most of the valley's water supply comes from mountain watersheds in the form of spring snowmelt, it has been necessary to build storage projects to capture the snowmelt and hold it for use in the summer months when the water demand is the greatest. In the early 1900s, Salt Lake City undertook the effort to build dams for municipal water supply storage. In 1917, Mt. Dell Dam, Lake Mary and Twin Lakes dams were constructed to store drinking water supply. By the early 1930's Salt Lake City looked beyond the local canyons to build dams. Today these storage reservoirs are as important as they were when first constructed.

Under the 1902 Water Reclamation Act, the Bureau of Reclamation was considering a dam on the Provo River.  In 1935, the City formed the Metropolitan Water District of Salt Lake City (MWDSLC) to participate in the construction of the Provo River Project and the 151,000 acre-foot Deer Creek Reservoir on the Provo River. The Salt Lake Aqueduct conveyed the stored water to Salt Lake City.  The 100 million-gallon per day Little Cottonwood Water Treatment Plant was completed in 1960. This project would be the major stored water supply for the valley's east side.

In 1967, the Central Utah Water Conservancy District (CUWCD) was formed to sponsor the $2.5 billion Central Utah Project that would capture a portion of the state's Colorado River allocation. Under the Bonneville Unit of the project, water collected from the Uinta Basin that would otherwise flow to the Colorado River is conveyed to the Wasatch Front through a series of reservoirs and aqueducts. The Jordanelle Reservoir, located on the Provo River upstream from Deer Creek Reservoir is the cornerstone of the project. Holding over 300,000 acre-feet of stored water, it will provide the Jordan Valley Water Conservancy District (JVWCD) 50,000 acre-feet and MWDSLC 20,000 acre-feet of M&I water supply. As part the project the Jordan Aqueduct was constructed to convey project water to Utah and Salt Lake Counties. The diversion on the Provo River at the Ohmsted diversion conveys water through the Ohmsted penstock, then into the Jordan Aqueduct that traverse Utah County then along the western side of Salt Lake County, terminating at 3800 West 2100 South, Salt Lake City. The 180 million-gallon per day Jordan Valley Water Treatment Plant treats and delivers water along the valley's west side.

Side view of the 69-inch Salt Lake Aqueduct on view at the MWDSLC Little Cottonwood Water Treatment Plant.

These two treatment and conveyance systems are the key elements that today deliver stored water to Salt Lake County residents. It's through the manipulation of flows through these aqueducts that make it possible to conjunctively deliver water supply within Salt Lake County.

In 1992, the 20,500 acre-foot Little Dell Reservoir was completed and is a key reservoir in providing water to Salt Lake County. It allowed water capacity to be made available up-stream on the Salt Lake Aqueduct for others to use.

1989 Conjunctive Management Agreement

The MWDSLC owns 100 percent of the Salt Lake Aqueduct and Little Cottonwood Water Treatment Plant. The JVWCD owns 5/7^th and MWDSLC 2/7^th of the Jordan Aqueduct and Jordan Valley Water Treatment Plant.  In 1989 Sandy City was de-annexed from the JVWCD and annexed into the MWDSLC. As part of that process, the informal process of cooperation was formalized under the terms of the "Conjunctive Water Management Plan." The late Attorney Ed Clyde, who mediated Sandy City's annexation into the MWDSLC, coined the term.

Salt Lake City, Sandy City, MWDSLC and JVWCD would cooperate to the extent possible in delivering water to Salt Lake County residents, would jointly plan together for the future and entered into boundary agreements. Included were the transfer of water capacities in the Jordan and Salt Lake Aqueducts. Conjunctive water management between the major water entities assures the public that all available capacity is being utilized and water delivered efficiently throughout the entire county regardless of ownership and preferential rights of the facilities. This endeavor is credited, in part, for avoiding water restrictions during the 1988-1992 drought.

The agreement expires in 2002, and at that time a new agreement will be adopted. Currently negotiations are underway to develop the new agreement. Both MWDSLC and JVWCD are implementing master plans to construct new facilities to meet the future needs of their customers. The new agreements are key to the timing of new facilities. 

The Summer of 2000

 A lower than normal winter snowpack, warm and early spring and a hot and dry summer have again proven the wisdom of conjunctive management within Salt Lake County.  Compounding the problem has been the enormous growth within the county.  Thus far this year, the JVWCD has experienced a 25 percent increase in water demand over last year. Salt Lake City's demand has increased by 12 percent. During the July 24 weekend, as distribution water reservoir levels dropped, the water managers got together to implement conjunctive water management adjustments.

Water system adjustments and aqueduct capacity transfers averted water shortages in parts of Salt Lake County. Large water users were asked to reduce their useage during a two-day period until the distribution reservoirs could recover. It's a normal operating practice, but points out the benefits of cooperation between the major water suppliers. Most don't understand the complexity and certainly not the level of cooperation that goes into providing drinking water to each customer's tap.

Questions regarding this article should be directed to: leroy.hooton@ci.slc.ut.us