For Johnson Creek near Ingram, the existing FIS flows are significantly lower than both the statistical and the HEC-HMS watershed modeling results at the 50-yr and 100-yr recurrence intervals. The statistical curves and the HEC-HMS watershed modeling results agree with one another for the more common (2-yr through 50-yr) events, but then the statistical curves trend significantly higher than the watershed model for the 100-yr and 500-yr recurrence internals. With only 114 square miles of drainage area, the 0.2% (500-yr) results from the watershed model seem more reasonable than the statistical results, which exceed 440,000 cfs at this site. Once again, the NOAA Atlas 14 rainfall values made very little difference in the results from the previous rainfall estimates.
Location summary from Watershed Hydrology Assessment for the Guadalupe River Basin
The final, recommended results are listed as such and may not be removed from the comparison figure, table, or the generated report for each site.
More than one frequency curve methods are available for some sites. If additional frequency curve methods are listed, click on the method name by the chart to toggle the frequency curve display. Any changes made to the chart will be included on the generated PDF.
[cfs, cubic feet per second; mi2, square miles; yr, year; %, percent]
| Annual Exceedance Probability | 50% | 20% | 10% | 4% | 2% | 1% | 0.50% | 0.20% |
|---|---|---|---|---|---|---|---|---|
| Return Period | 2-yr | 5-yr | 10-yr | 25-yr | 50-yr | 100-yr | 200-YR | 500-yr |
| Hydrologic Method | cfs | cfs | cfs | cfs | cfs | cfs | cfs | cfs |
Recommended Method
Frequency Curve Method DescriptionsAfter completing the hydrologic analyses by all the various methods described in the report, their results were compared to one another in terms of frequency peak flow estimates at the USGS streamgage locations and selected stream reaches within the basin. These comparisons of frequency flow estimates plot the estimated frequency curves at each gage along with their confidence limits and the previous published discharges from the effective Federal Emergency Management Agency (FEMA) Flood Insurance Studies (FIS).
Based on data published in the Watershed Hydrology Assessment for the Guadalupe River Basin report.
USGS streamgage names and drainage areas
Site names and drainage areas displayed on the website are based on the Watershed Hydrology Assessment for the Site Results. For USGS streamgages, these may not exactly match the official USGS names or drainage areas for a given location. In addition, the drainage areas shown in this application are rounded to the nearest whole number. For locations downstream from Canyon Lake dam, drainage area values include only the uncontrolled area downstream from the reservoir.