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H. R. Hejl

Publications and source records attributed to H. R. Hejl.

6 recordsLinked to original sources
USGS1996

Floods in Central Texas, December 1991

Record-breaking peak discharges were recorded at eight U.S. Geological Survey (USGS) streamflow-gaging stations in central Texas during December 1991 (fig. 1), and substantial peak discharges also occurred at numerous other stations. Large peak discharges during December are unusual in central Texas. The rainfall causing the flooding began on December 18, with 6-day totals exceeding 10 inches (in.) in the area of heaviest rainfall. This report documents peak discharges and runoff volumes during December 1991. Recurrence intervals were determined for the peak discharges and runoff volumes for 1-, 3-, and 7-day periods. A recurrence interval references the approximate number of years during which a given peak discharge or runoff volumes is expected to be equaled or exceeded only once. A flood of a given recurrence interval is defined on the basis of peak discharge – for example, a 100-year flood is defined as the peak discharge that has a 1-percent chance of being equaled or exceeded in any given year.

Texas↗
USGS1989

Application of the precipitation-runoff modeling system to the Ah-Shi-Sle-Pah Wash watershed, San Juan County, New Mexico

The precipitation-runoff modeling system was applied to the 8.21 sq-mi drainage area of the Ah-shi-sle-pah Wash watershed in northwestern New Mexico. The calibration periods were May to September of 1981 and 1982, and the verification period was May to September 1983. Twelve storms were available for calibration and 8 storms were available for verification. For calibration A (hydraulic conductivity estimated from onsite data and other storm-mode parameters optimized), the computed standard error of estimate was 50% for runoff volumes and 72% of peak discharges. Calibration B included hydraulic conductivity in the optimization, which reduced the standard error of estimate to 28 % for runoff volumes and 50% for peak discharges. Optimized values for hydraulic conductivity resulted in reductions from 1.00 to 0.26 in/h and 0.20 to 0.03 in/h for the 2 general soils groups in the calibrations. Simulated runoff volumes using 7 of 8 storms occurring during the verification period had a standard error of estimate of 40% for verification A and 38% for verification B. Simulated peak discharge had a standard error of estimate of 120% for verification A and 56% for verification B. Including the eighth storm which had a relatively small magnitude in the verification analysis more than doubled the standard error of estimating volumes and peaks.

New Mexico↗
USGS1980

Preliminary appraisal of ephemeral-streamflow characteristics as related to drainage area, active-channel width, and soils in northwestern New Mexico

Regression equations are presented to predict ephemeral streamflow characteristics in the San Juan Basin in northwestern New Mexico. The standard error of estimate for predicting runoff for water year 1978 using drainage area as the independent variable was 152 percent. Indications are that reliable equations for predicating annual runoff can be developed and the standard error of estimate might be reduced significantly with additional years of record. The coefficient of regression when relating drainage area to runoff for water year 1978 was significant at the 1-percent level. Preliminary results also indicate it is feasible to predict streamflow characteristics using hyrologic soil-group classifications based on runoff potential. The standard error of estimate for predicting peak discharges with recurrence intervals of 2, 5, 10, 25, 50, and 100 years using active-channel width as the independent variable averaged about 50 percent, and the regression coefficient was significant at the 1-percent level. Using drainage area to predict peak discharges resulted in a standard error of estimate that averaged about 60 percent and a regression coefficient significant at the 5-percent level. The standard error of estimate averaged about 45 percent when active-channel width and drainage area were related to peak discharges in multiple regression analyses. (USGS)

Open-File Report↗
USGS1977

A method for adjusting values of Manning's roughness coefficient for flooded urban areas

A method is presented for adjusting values of Manning's roughness coefficient for flooded urban areas on the basis of the density of buildings on a flood plain and verified roughness coefficients for natural conditions. An urban roughness coefficient can be calculated to emulate the water-surface profiles to within 0.06 meter for depths of flow less than 0.6 meter and plus or minus 10 percent for depths between 0.6 and 2 meters.

Journal of Research of the U.S. Geological Survey↗