Don Pedro Dam:
Dam Web page created by Sukhwant Virk and Josh Hinkey as a Civil Engineering class project. Photographs
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Don Pedro General Information

Dam Location and Directions

Ownership and Operators

The dam is currently owned by the Turlock Irrigation District (TID) and Modesto Irrigation District (MID) and operated by the TID Board of Directors.

Technical Contact

Randy Baysinger, Supervising Engineer:  (209) 883-8232

Tour information

TID does not give tour of the dam, but Don Pedro Recreational Agency displays demos of the dam:
Contact Don Pedro Recreational Agency @  (209) 852-2396.

Contact TID @ (209) 883-8356

The Yosemite National Park will be conducting a tour of several California dams from August 16 to August 19, 1999.  The tour consists of a day and a half stay in Yosemite Park, some visits to major storage projects, a major pumping plant tour, and two dams tours (Fraint and Don Pedro). The fourth day will consist of a tour of the Don Pedro Dam facilities (demos displayed by the Recreational Agency).  Transport is a bus at cost of $600 (double occupancy) and $800 (single).  Individual questions regarding return flights arrangements can be directed to kelly Scales of  Travel Associates at (415) 383-7200 or fax (415) 383-5232.

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Don Pedro Dam Design and Construction:

Construction type

Construction date Dam Spillway
    Type:                  Gated Overflow (operated by a gantry crane capable of lifting 125 tons)
                               Emergency Weir
    Crest elevation:    855 ft MSL
Outlet Reservoir Hydropower Generation

After the completion of the Old Don Pedro Dam in 1923, the powerhouse was capable of producing up to 15 megawatts of power.  It was the first hydroelectric powerhouse in the nation to use a two circuit, 66,000 volt, aluminum power line.  The capacity of the each generator was upgraded to 30 megawatts in 1926.  New Don Pedro Dam was completed in May of 1971, and the new powerhouse could generate up to 165 megawatts of electricity by utilizing three "Francis" type hydroelectric turbine generators.  A fourth generator was added in 1989 that enabled the powerhouse to generate up to 203 megawatts of electricity.

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Don Pedro Dam Current Uses and Operations:

Reservoir Background

On February of 1920, the MID and TID voters approved three bonds worth $4.1 million dollars to construct the Don Pedro Dam.  So, on June 25, 1921 the construction of the Dam would began, and in 1923 it would be finished.  The dam would be constructed to a height of 284 feet, making it  the tallest dam in the world in 1923.  The end result would be a reservoir, that would provide water storage, flood control, and power production for the MID and TID.

Yet, in 1971 the dam would be modified to meet the increased agricultural and population demand.  By contributions from the City and County of San Francisco Hetch Hetchy Water and Power, TID, MID, financial assistance from the U.S. Crops of Engineers and California Department of Water Resources, the new Don Pedro Dam would be modified to 580 feet in height.  The new Don Pedro Dam would increase the reservoir capacity by seven times, making it the six largest body of water in the State of California.  The reservoir would extend 26 miles in length with capacity of 2.03 million acre feet.  Also, when full, the reservoir water level would be at 830 feet above see level generating 203 megawatts of peak electricity.  The MID would be entitled to 31.54% of the total electricity produced, while TID would be entitled to the rest.

Now the reservoir is also a great source of recreational opportunities, attracting over 400,000 visitors per year.  Recreational activities include fishing, boating, sailing, water skiing and camping.

Reservoir Storage and Flood Control

The New Don Pedro reservoir has 2,030,000 acre-feet of maximum water storage.  This makes it the sixth largest body of water in California.  The downstream channel capacity is designed to handle 15,000 cfs of release flow.  The system is supposed to protect homeowners adjacent to the Tuolumne River, downstream from Don Pedro.

Even with over 2 million ac-ft of storage Don Pedro has one of the smallest flood control buffers in the state.  The available flood control storage is only about 340,000 ac-ft because the dam was designed to meet the electrical demands during the summer months.  This translates to only about 9,000 cfs of flow diversion during peak periods of runoff.  The flood control buffer is set at only 17% of the full storage capacity of Don Pedro.  It has been estimated by the FEAT (Flood Emergency Action Team) that this will only provide a 55 year level of protection.  In other words, every 55 years there is a high probability that a flow larger than 9,000 cfs will pass through the system and damage downstream levees.  There is a need to re-engineer this system to protect future damages along the Tuolumne River basin.

For example, there have been several flows discharged through the reservoir exceeding the operating capacity and flooding residents downstream.  In January, 1997 the reservoir filled and the releases peaked at 50,000 cfs, causing massive flooding and levee damage downstream.

Major Floods on Record
Date Max 1-day (cfs) Ave 3-day (taf)
Dec - 64 72,000 306
Feb - 86 53,000 294
Jan - 97 120,000 548

Water Deliveries

Each year the Don Pedro dam releases water into Tuolumne River and roughly after 2 miles, at the La Grange Dam approximately 885,000 acre-feet of water is diverted to the MID and TID main canals.  The canals deliver about 575,000 acre-ft of water to the south through the foothills and into the regulating reservoir at Turlock Lake for TID, and about 310,000 acre-feet of water to the north to the regulating reservoir at Modesto lake for MID.

TID than deliveries drinking water to about 70 people in the town of La Grange and the other 99.99% of water to farmers through various canals on basis of need.  The canal could accommodate water flows of approximately 2,000 cubic feet per second. During the months of March through October, the Don Pedro water flows provide approximately 300,000 acre-feet of water to 5,800 farmers within 305 square mile irrigation service area of Turlock Irrigation District.  These flows nourish more than 30 high value crops, ranging from almonds to sweet potatoes.

MID provides irrigation water to approximately 64,000 acres, nourishing corps such as almonds, grapes, walnuts, peaches, and tomatoes, and animals such as chickens, cattle, calves, and turkeys.  A very small percent of the water is used to supply drinking water to the Stanislaus County.

Water Transfers

Each year approximately 310,000 ac-ft of water is diverted to MID, 575,000 ac-ft to TID, 230,000 ac-ft to San Francisco Hetch Hetchy Water and Power, and 780,000 ac-ft to Tuolumne river.

The water supplied by Don Pedro is distributed to the farmers in the Tuolumne basin and other nearby basins.  Water is available to those who want to purchase it through the Turlock Irrigation District at a price of 10$/acreft.  Excess supplies of water that occur during heavy rain seasons are sold for 15$/acreft.  There is a 48 in per acre allotment.

Fisheries Flows

The minimum fishery flows below the dam are maintained per an agreement between the TID, MID, City of San Francisco, Dept. of Fish and Game and other under the FERC Agreement 2299.  Base flows range from 50 cfs to 300 cfs, depending on the time of the year and water year type.

Recent operating challenges

There is an existing balance between the power supplied, the quality and quantity of water supplied, and the amount of flood control provided by Don Pedro Reservoir.  The current water year is projected to completely fill Don Pedro Reservoir.  There is expected to be high runoff flows throughout the summer months.  One challenge will be  lower the lake level and ensure flood protection.  This will be against the will of the farmers demanding cheap water.

Concerns for future operations

The current level of flood protection is inadequate for the rate of development in the Tuolumne River Basin.  The downstream levees need to be engineered to handle larger releases and the operating capacity must be modified to protect against flood damages.  Power supply, irrigation demands, and recreational demands are fighting to keep the surface elevation of the reservoir high.  However, increasing flood control has become a priority due to recent flood events.  Therefore, a more balanced operating strategy is in need.  The operating rule must give more weight to flood control and less weight to revenue generation.

Environmental conditions have been suspect to new government regulation, causing another shift in demand.  New operating rules must include the environmental demands while maintaining the current water supplies.

There must be improved facilities designed to meet the increasing supply needs as the Tuolumne river basin grows in population.  Both structural improvements and technical improvements will help to conserve water.  The promotion of conservation through education is one example of a demand management strategy.

To account for the heavy water demand on ground waters during droughts, groundwater recharging has also become an important responsibility for water allocation.  New policies need to account for groundwater recharging during the wet years to supply water during the droughts.
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Don Pedro Data Links

               1 Month                           Water Year 99
               Water Year 98                 Water Year 97 Other Cool Links Dam References Contact the Web Builders

            Josh Hinkey
            Sukhwant Virk
            Instructor:  Jay Lund

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Special thanks to Jim Freschi.