Duchesne River Hydrology and Water Availability Study

FINAL

Prepared for:

Management Committee of the
Recovery Implementation Program
for Endangered Fish Species in the
Upper Colorado River Basin

Prepared by:

CH2M HILL

September, 1997

Funds for this study were provided by the Recovery Implementation Program.  Central Utah Water Conservancy District acted as the contracting agency in order to complete the study.

Background

The United States Fish and Wildlife Service (USFWS) has identified Duchesne River flows as having potentially significant benefits to endangered fish.  The lower 2 ½-miles of the Duchesne River have been designated as critical habitat for the razorback sucker.  The Management Committee of the Recovery Implementation Program for Endangered Fish Species in the Upper Colorado River Basin (RIP) authorized funding for a comprehensive review of the effects of existing and proposed projects on the flow regime in the designated critical habitat reach of the Duchesne River.  The Central Utah Water Conservancy District (CUWCD) acted as the contracting agent to complete the study with RIP funds.  This report is the compilation of this study. 

As will be discussed herein, the study provides information on flows in the lower Duchesne River as published by the United States Geological Survey (USGS).  This data is actual data from 1943 to 1994 with data correlated back to 1912 using the data from the Myton gage.  This data is compared to the United States Bureau of Reclamation (USBR) pre-development flows which estimate flows without influence from man.  The difference between these two sets of data is considered to be the depletion from the river.  Future depletions are discussed and estimated data presented.  Comparisons of flows in the river are made to USFWS preliminary recommended flows to determine deficiencies.

Study Purpose and Objectives

The main purpose of the study was to determine the effect of existing projects (both existing and future operation) on Duchesne River flows and to identify possible water sources on the Duchesne River that could be used to augment river flows, if needed, to meet USFWS endangered fish preliminary flow recommendations.

The study objectives are described below:

·         To determine present flow regime on lower Duchesne River

·         To determine historical changes to that flow regime

·         To identify flow surplus or deficiencies of present flow regime with respect to USFWS identified flows

·         To locate potential water sources to meet any needed flow deficiencies

Summary of Agency Workshops

Five workshops were held with  federal and state agencies, water agencies, water users, and other interested parties to discuss the study, its methods, the scope of work, study objectives, and to share knowledge among the group.  As study results became available, they were shared.  The five workshops were held on April 25, May 31, June 28, August 7, and September 9, 1996.  Complete meeting notes, copies of material presented, and attendance lists for each of the meetings are included in the Appendices.

Flow Analysis of the Duchesne River

An examination of impacts, with changing operation on the Duchesne River, was done by dividing the record into two periods (pre-1970, post-1970) to develop statistics for each period.  The pre-project period was assumed to represent historical flow regime, and the post-project period was assumed to reflect current flow regime with increased diversions from such projects as CUP.  There is no defined date when the flow regime changed from historical flow regime, because the change was incremental.  Major changes occurred with the CUP project coming online in 1970.  Thus, the pre-project and post-project periods are assumed to be pre- and post- 1970, respectively.  To assist in determining pre-project flows and the effects of longer term record, the Myton gauge was used to extend the flow record of the Randlett gauge to earlier periods with less development.

Extending the flow record for the Randlett gauge was accomplished by making a linear correlation with the Duchesne River at Myton stream gauge.  The extended record shows (approximately) a 20 percent increase in pre-project average flows with an average volume of 533,700 acre-feet.  Flow statistics for the various periods are summarized in the table below.

Table ES-1

Duchesne River at Randlett

Review of USBR Pre-Development Flows

An analysis of the Duchesne River has been performed by the USBR to determine “Pre-Development Flows” of the Colorado River Basin.  These flows were developed by the USBR for the whole Colorado River Basin in an attempt to develop virgin river flows.  These were developed primarily to be used in compact issues on the Colorado River among the states.  They historically have been updated every 5 years. The average yearly flow for the period of record from 1912-1990 is 768,000 acre-feet.  This compares to an average yearly flow of 498,000 acre-feet for the same period of record at the Randlett gauge, or a long-term difference of 270,000 acre-feet per year.  This value would represent theoretical depletions from the Duchesne River system from all human activities caused by man.

The average yearly flow difference between the USBR flows and the Randlett gauge are shown below for various periods of record.

Table ES-2

Yearly Flow Difference (Between USBR Pre-Development Recommendations and Randlett)

Flow Analysis of the Duchesne River With Full Bonneville Unit Operation

The Strawberry Aqueduct of the Bonneville Unit of the CUP diverts water from the Duchesne River Basin into the Great Basin via Strawberry Reservoir.  The Starvation Collection System diverts water into Starvation Reservoir for distribution in the Uintah Basin.  The Bonneville Unit has been under construction for over 30 years.  Diversions into Strawberry Reservoir began in December 1971, with small amounts of water delivered to the reservoir until 1985, with the completion of remedial work at Soldier Creek Dam.  Completion of the entire collection system did not occur until final work at Stillwater Reservoir was completed in 1989.  Bonneville Unit project deliveries to Strawberry Reservoir have been at capacity since 1989, with the exception of minor releases at Rock Creek due to remedial work on the Upper Stillwater Dam.  Diversion into Starvation Reservoir began in December 1969.  The Bonneville Unit depletions from the Duchesne River average 143,200 acre-feet annually.

Flow Analysis of the Duchesne River With Uintah Basin Replacement Project Proposed Operation

The Uintah Basin Replacement Project (UBRP) is a water development project proposed by the CUWCD to replace the Upalco and Uintah Units of the CUP in northeastern Utah.  The project will, in part, assist the Ute Indian Tribe of the Uintah and Ouray Reservation in the development and management of water resources.  The project will also provide early and late season irrigation water, and water for environmental purposes for fishery flows.  The UBRP consists of two units, the Upalco and Uintah Units. 

The UBRP is expected to impact the lower Duchesne River by depleting additional flows from the river.  These total expected depletions are shown in the table below.

Table ES-3

UBRP Depletions

USFWS Preliminary Flow Recommendations

The USFWS preliminary flow recommendations for the Duchesne River were provided in a January 23, 1995, letter to the CUWCD and a March 9, 1995, memorandum to John Hamill, Program Director of the RIP.  The March 9, 1995, memorandum was a modification of the January 23, 1995, letter.  Recommendations were further augmented with additional information from the workshop meetings held during this study.  USFWS letters and correspondence describing their flow recommendations are located in the Appendices. 

Due to limited available biological information specific to the Duchesne River, flow recommendations were based solely on hydrologic data.  The hydrologic data used for the flow recommendations were developed for each month using exceedance values of 75, 50, and 25 percent.  The exceedance values were determined using daily values from the period of 1944 through 1964.  The 25, 50, and 75 percent exceedance values are classified as flow recommendations for wet, average, and dry water years, respectively.  The USFWS preliminary flow recommendations are shown in the table below with the USFWS flows calculated in ac-ft per month in the second part of the table.

Table ES-4

USFWS Preliminary Flow Recommendations

The recommendations for channel scouring and maintenance flows were modified in the March 9, 1995, memorandum.  The recommended channel scouring flows are 2,800 to 3,000 CFS once every 4 years and recommended channel maintenance flows averaging 1,500 to 1,800 CFS in the other 3 years.  The January 23, 1995, letter stated that the lower value would be a target flow for an average water year and the higher value would be for an above-average water year.  The duration for these modified flow recommendations is not specified in the March 9, 1995, memorandum.  The January 23, 1995, letter recommends that the events be a minimum of 2 weeks.

The preliminary flow recommendations from the USFWS are their best attempt without more specific biological, and other types, of data.  Results from future studies were identified to be critical in determining and refining the preliminary flow recommendations for the Duchesne River.

Comparison of Historic Randlett Flows to USFWS Preliminary Recommended Flows

A comparison of the USFWS preliminary flow recommendations with historical flows at Randlett was made to determine flow deficiencies that would have occurred over the period of record (1912-1994). 

Analysis of the flow volume required to meet USFWS preliminary flow recommendations, under a dry year scenario for the period of record, was accomplished by looking at the yearly deficiencies in dry years.  The flow volume needed does not necessarily equal the cumulative difference for the entire year as shown in the table below.  Most of the yearly totals are influenced by the summer months of July, August, and September having higher flows than the USFWS preliminary flow recommendations.  These reduce the total yearly deficiency.  However, the critical amount required equals the total monthly deficiencies during the period from October through May.  This is the amount that would be needed in storage, or result from reduced flows going into storage. 

There are several years during the extended period of record from 1912-1994 when the USFWS dry year preliminary flow recommendations were not met and would have required additional water in the Duchesne River during some periods of these years.  These years include the early 1930s, 1959-1961, 1977-1980, and the period from 1989-1994.  The most critical period has been the recent drought years from 1989-1994, which coincides with years the Bonneville Unit was essentially under full operation.  This period was used to determine the potential maximum amount of water that would be needed to meet the USFWS dry year preliminary flow recommendations in any one year.  For the period from 1989 to 1994, the flow needed monthly and annually to meet the USFWS preliminary flow recommendations is shown below.  Values in parentheses represent differences between recommended and existing flows in the Duchesne River.

Table ES-5

Flow Differences USFWS to Actual Dry Year

The average annual flow deficiency during the period from 1989-1994 is over 91,000 acre-feet per year, with a peak year in 1990 of approximately 129,000 acre-feet.  As can be seen from the above table, the flow deficiencies primarily occur in the period from November through June.  For the November through June period during 1989-1994, the flow deficiency is over 103,000 acre-feet with a peak of 134,000 acre-feet in 1990.  Of the flow deficiency during 1989-1994,  an average of approximately 60,000 acre-feet occurs in the winter months from November to April.  With these deficiencies occurring in the winter months, potential sources of water to meet these deficiencies can only come from two sources, water in storage or winter flows that are now going into storage in the system. The peak flow requirement of 134,000 acre-feet represents 50 percent of the long-term (1912-1990) average depletions on the Duchesne River of 270,000 acre-feet.

Determination of Potential Sources of Water

As is the case with the main stem of the Colorado River, water in the Duchesne River has been diverted and put to beneficial use under state law.  The cycle of diversion, use, and flows returning to the river occurs several times as the river flows down the system.  As is very evident from the results of the study, sufficient water to meet the USFWS preliminary flow recommendations is not available given current use.  This is true for both monthly and annual flows.  In this report, we discuss possible sources that could potentially augment flows in the river without attempting to match the difference between existing flows and the USFWS preliminary recommended flows.

Some of the potential sources of water examined in this report include existing Bonneville Unit fishery flows, potential Daniels Creek diversions, land purchase and fallow;  conservation projects such as water delivery improvement projects (such as canal lining or piping), on-farm conservation improvements such as sprinkler systems, and purchase of water in existing storage facilities.  Each of these potential sources are summarized in the table below.

Table ES-6

Potential Water Sources

Study Results and Conclusions

·         The long-term average flow (1912-1990) in the Duchesne River at Randlett has averaged 498,000 acre-feet.

·         The USBR’s pre-development theoretical flows show the virgin flows of the Duchesne River for the same period (1912-1990) averaging 768,000 acre-feet.

·         Long-term depletions on the Duchesne River at Randlett, calculated using the USBR’s pre-development flows, have been 270,000 acre-feet.

·         Since 1970, depletions have increased on the Duchesne River, with average depletions at 342,000 acre-feet.

·         Over the life of the project, the Bonneville Unit will, on average, annually deplete 143,200 acre-feet from the Duchesne River system.

·         The UBRP Project is anticipating additional depletions to the Duchesne River system of 25,300 acre-feet per year.

·         The USFWS preliminary flow recommendations for wet, average, and dry years in total will require 555,000; 338,000; and 184,000 acre-feet of water on a yearly basis at the Duchesne River Randlett gauge.

·         The USFWS preliminary flow recommendations are based solely on hydrology with no biological data to determine the actual needs of the fish.

·         During dry years, including the recent period of 1989-1994, the USFWS preliminary recommended flows, if met at Randlett, would require up to 134,000 acre-feet of water to be acquired in the system.

·         There are a number of potential sources of water in the Duchesne River Basin, however, most would require the purchase of water rights either directly or through land fallowing.

·         Water from the various sources, if purchased, would be at a cost of $1,000 to $1,500 per acre-foot or market value, if the water is available for purchase.

·         The study group (associated with this study) supports the efforts to fund biological studies to provide data for determining flows needed by the endangered species.

·         The study group supports the correlation of the best scientific data (geomorphology, biology, hydrology), to determine needed fishery flows.