By William H. Asquith and Raymond M. Slade, Jr.

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5 | Asquith: txfreq.sun
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TEXAS SITE-SPECIFIC FLOOD FREQUENCY PROGRAM

version 1.01

U.S. Geological Survey, Austin, Texas

developed in cooperation with the Texas Department of Transportation

This program computes estimates of T-year floods for ungaged stream sites within natural basins in Texas based on a non-fixed boundary generalized least-squares multivariate regression. The user enters a site identifier, latitude and longitude, drainage area and other basin characteristics for the ungaged site. The program selects gaged sites with similar basin characteristics and performs a multivariate generalized least-squares regression analysis.

Selection Option:

Warning No. 1 --> (1) Different T-year Discharges

Warning No. 2 --> (2) Use of Resulting Equation

Continue Program --> (3) ---

**3**

Enter file name for FULL output:

**example_for_text_full.out**

Enter file name for SUMMARY output:

**example_for_text_sum.out**

Enter file name for STATION DATA output:

**example_for_test_sta.out**

English or Metric units (E/M)?

**e**

Enter site id (up to 30 characters)

**Guadalupe River site for example in text**

Enter site latitude (dd mm ss)

**29 58 10**

Enter site longitude (dd mm ss)

**98 53 33**

Enter drainage area, shape, slope (mi^2, --, ft/mi)

(enter a value less than or equal to zero if unknown)

**839 5.65 15.01**

Summary of the ungaged site: Guadalupe River site for examp
Latitude: 29.d 58.m 10.s
Longitude: 98.d 53.m 33.s
Drainage Area = 839.
Basin-Shape Factor = 5.6500001
Stream Slope = 15.0100002

Enter no. of stations to 'pool' or regionalize together

**30**

Use only DRAINAGE AREA otherwise SLOPE and SHAPE

will also be considered (Y for AREA/ N for ALL)

**n**

Program considering AREA, SHAPE, and SLOPE

Station Selection Criteria (see text for more details):

(1) PROXIMITY: Drainage Area bounded by 1.5 log10 cycles

(2) SIMILARITY: Drainage Area, Basin Shape, Stream Slope, and Distance

(3) SIMILARITY: Drainage Area and Distance

Enter (1,2,3) or (1,3 only if no shape or slope):

**1**

IMPORTANT NOTE--

It is important that all the peak-streamflow frequency should be based on the same execution of the program using the same assumptions, in order to minimize the possibility of producing discharge values that would not be appropriately proportional to their recurrence interval.

Also, it is inappropriate to select the T-year estimate from one run of the program and a different T-year estimate from another run of the program.

By using all T-year estimates from one run, the user is unlikely to encounter the situation in which the streamflow value for one recurrence interval is LARGER than the streamflow value for a HIGHER recurrence interval.

664 stations were read in

The concurrent record matrix has been filled

Std Deviations of independent variables calculated

Calculating distances to all 664 stations

BEGIN GLS REGRESSION

UNGAGED SITE PREDICTION (cubic feet per second)
T-year Prediction
2-year 11526.30
PREDICTION ERRORS AND LIMITS Sqroot (log10)
Standard Error of Prediction: 45.59 percent
Std Error Variance of Prediction: 0.0356 ---> 0.1887
Sampling Error Variance of Prediction: 0.0026 ---> 0.0505
Prediction Limits Upper Lower
90-percent 24142.4062 5502.99561 Limits are two-
67-percent 17731.9844 7492.42383 tailed, or ___%
50-percent 15509.0986 8566.30176 bounding limits.

UNGAGED SITE PREDICTION (cubic feet per second)
T-year Prediction
5-year 34333.87
PREDICTION ERRORS AND LIMITS Sqroot (log10)
Standard Error of Prediction: 27.67 percent
Std Error Variance of Prediction: 0.0139 ---> 0.1180
Sampling Error Variance of Prediction: 0.0019 ---> 0.0433
Prediction Limits Upper Lower
90-percent 54539.3047 21614.0352 Limits are two-
67-percent 44951.707 26224.0195 tailed, or ___%
50-percent 41337.3398 28516.9395 bounding limits.

UNGAGED SITE PREDICTION (cubic feet per second)
T-year Prediction
10-year 56603.20
PREDICTION ERRORS AND LIMITS Sqroot (log10)
Standard Error of Prediction: 24.54 percent
Std Error Variance of Prediction: 0.0110 ---> 0.1050
Sampling Error Variance of Prediction: 0.0019 ---> 0.0433
Prediction Limits Upper Lower
90-percent 85462.9609 37489.0156 Limits are two-
67-percent 71949.2188 44530.3281 tailed, or ___%
50-percent 66775.3203 47980.6406 bounding limits.

UNGAGED SITE PREDICTION (cubic feet per second)
T-year Prediction
25-year 95543.52
PREDICTION ERRORS AND LIMITS Sqroot (log10)
Standard Error of Prediction: 26.06 percent
Std Error Variance of Prediction: 0.0124 ---> 0.1113
Sampling Error Variance of Prediction: 0.0023 ---> 0.0479
Prediction Limits Upper Lower
90-percent 147852.906 61740.8555 Limits are two-
67-percent 123200.211 74095.3594 tailed, or ___%
50-percent 113832.133 80193.2109 bounding limits.

UNGAGED SITE PREDICTION (cubic feet per second)
T-year Prediction
50-year 129000.65
PREDICTION ERRORS AND LIMITS Sqroot (log10)
Standard Error of Prediction: 27.02 percent
Std Error Variance of Prediction: 0.0133 ---> 0.1153
Sampling Error Variance of Prediction: 0.0027 ---> 0.0516
Prediction Limits Upper Lower
90-percent 202908.438 82013.1875 Limits are two-
67-percent 167899.172 99114.0547 tailed, or ___%
50-percent 154678.094 107585.805 bounding limits.

UNGAGED SITE PREDICTION (cubic feet per second)
T-year Prediction
100-year 171309.83
PREDICTION ERRORS AND LIMITS Sqroot (log10)
Standard Error of Prediction: 31.89 percent
Std Error Variance of Prediction: 0.0183 ---> 0.1351
Sampling Error Variance of Prediction: 0.0034 ---> 0.0579
Prediction Limits Upper Lower
90-percent 291301.75 100744.539 Limits are two-
67-percent 233311.5 125784.883 tailed, or ___%
50-percent 211927.172 138477.094 bounding limits.

END OF ANALYSIS

Writing the data for the 30

6 | Asquith:

Return to the WRIR 99-4172 homepage

For more information, contact Will Asquith

Last modified August 31, 1999

URL: https://water.usgs.gov/lookup/get?wri994172