In cooperation with the Texas Department of Transportation
Effects of Regulation on L-moments of Annual Peak Streamflow in Texas
By William H. Asquith
U.S. Geological Survey
Water-Resources Investigations Report 01–4243
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Contents
Abstract
Introduction
Purpose and Scope
U.S. Geological Survey Streamflow Data
Texas Natural Resource Conservation Commission Reservoir Data
Approach
Study Methods
Peak-Streamflow Frequency Analysis
Variables Representing Regulation
Comparison of Annual Peak Streamflow for Static Periods of Regulation
Analysis of Trends
Effects of Regulation on L-moments of Annual Peak Streamflow
Estimating L-moments of Natural Annual Peak Streamflow
Quantifying Regulation Effects on L-moments of Natural Annual Peak Streamflow
Adjusting L-moments of Natural Annual Peak Streamflow for Potential Regulation Effects
Summary
Selected References
Plates
| 1–2. |
Maps showing: | |
1. |
Location of U.S. Geological Survey streamflow-gaging stations
used in analysis pdf 17 " X 18" (686 KB) |
|
2. |
Location of dams in Texas Natural Resource Conservation Commission inventory
of dams used in analysis pdf 17 " X 18" (3.63 MB) |
|
Figures
| 1–2. |
Maps showing: | |
1. |
Location of 367 streamflow-gaging stations with at least 10 years of annual peak-streamflow data through 1997 (designated as natural by 10-percent criterion) | |
2. |
Location of 96 streamflow-gaging stations with at least 10 years of annual peak-streamflow data through 1997 (designated as regulated by 10-percent criterion) that have static periods of regulation suitable for comparative analysis | |
3–13. |
Graphs showing: | |
3. |
Example of time series of cumulative changes in regulation for station 08136500 Concho River at Paint Rock, Texas | |
4. |
Relation between (a) change in maximum capacity, (b) change in normal capacity, and (c) change in difference between maximum and normal capacity to contributing drainage area in all regions | |
5. |
Relation between (a) change in maximum capacity, (b) change in normal capacity, and (c) change in difference between maximum and normal capacity to contributing drainage area in northeast region | |
6. |
Relation between (a) change in maximum capacity, (b) change in normal capacity, and (c) change in difference between maximum and normal capacity to contributing drainage area in southeast region | |
7. |
Relation between (a) change in maximum capacity, (b) change in normal capacity, and (c) change in difference between maximum and normal capacity to contributing drainage area in west region | |
8. |
Relation between change in mean annual peak streamflow to (a) change in maximum capacity and (b) change in normal capacity | |
9. |
Relation between change in L–CV of annual peak streamflow to (a) change in maximum capacityand (b) change in normal capacity | |
10. |
Relation between change in L-skew of annual peak streamflow to (a) change in maximum capacity and (b) change in normal capacity | |
11. |
Relation between (a) change in mean annual peak streamflow and (b) change in L–CV of annual peak streamflow to change in difference between maximum and normal capacity | |
12. |
Relation between change in L-skew of annual peak streamflow and change in difference between maximum and normal capacity | |
13. |
Relation between (a) change in mean annual peak streamflow and (b) change in L–CV of annual peak streamflow to contributing drainage area | |
Tables
1. |
Streamflow statistics and basin characteristics for 367 USGS streamflow-gaging stations with at least 10 years of annual peak-streamflow data through 1997 (designated as natural by 10-percent criterion) |
2. |
Static periods of regulation suitable for comparative analysis for 96 USGS streamflow-gaging stations with at least 10 years of annual peak-streamflow data through 1997 (designated as regulated by 10-percent criterion) |
3. |
Texas Natural Resource Conservation Commission permitted dams with maximum capacities in excess of 10,000 acre-feet |
4. |
Regression equations for estimation of L-moments and L-moment ratios of annual peak streamflow for three regions in Texas |
Abstract
Several techniques exist to estimate annual peak-streamflow frequency for streamflows that have recurrence intervals ranging from 2 to 500 years for natural (unregulated) drainage basins in Texas. Unfortunately, such techniques have limited applicability in regulated basins. There are numerous regulated basins throughout Texas, which has more than 7,000 dams that are identified by Texas Natural Resource Conservation Commission permits. The effects on annual peak streamflow from reservoirs created by these dams range from negligible to the complete suppression of the flood hydrograph; also, reservoirs can artificially create flood-like hydrographs. The large number of reservoirs and their widespread distribution in Texas necessitate an assessment of flood characteristics in regulated basins. Therefore, the U.S. Geological Survey, in cooperation with the Texas Department of Transportation, conducted a study of the effects of regulation on L-moments of annual peak streamflow in Texas.
For this report, the State was divided into three regions. Four regression equations to estimate the L-moments of natural annual peak-streamflow data for ungaged sites were derived for each region from data for 367 streamflow-gaging stations in natural basins. The explanatory variables in the equations are contributing drainage area, basin shape factor, and stream slope.
The effects of regulation on the L-moments of annual peak-streamflow data were determined by analysis of maximum and normal storage-capacity data from reservoirs for 96 streamflow-gaging stations in variously regulated basins. The results indicate that as potential flood storage (defined by the difference between total maximum and normal capacity) in a basin increases, the mean annual peak streamflow decreases nonlinearly. Evidence strongly indicates (despite contrary expectation) that the higher L-moments (coefficient of L-variation, L-skew, and L-kurtosis) are unaffected by regulation.
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