Comparisons of Estimates of Annual Exceedance-Probability Discharges for Small Drainage Basins in Iowa, Based on Data through Water Year 2013, TR-678, 2015

(2015) Comparisons of Estimates of Annual Exceedance-Probability Discharges for Small Drainage Basins in Iowa, Based on Data through Water Year 2013, TR-678, 2015. Transportation, Department of

pdf
Preview
PDF
IADOT_TR_678_USGS_2015_5055_Eash_Annual_Exceedance_Probability_Discharges_Small_Drainage_Basins_Iowa_Water_Year_2013_2015_Final.pdf

File Size:2MB
pdf
Preview
PDF
IADOT_TR_678_USGS_2015_5055_Eash_Annual_Exceedance_Probability_Discharges_Small_Drainage_Basins_Iowa_Water_Year_2013_2015_Tech_Brief.pdf

File Size:246kB
pdf PDF
sir2015-5055_table03.xlsx

File Size:49kB
pdf PDF
sir2015-5055_table04.xlsx

File Size:33kB
pdf PDF
sir2015-5055_table08.xlsx

File Size:33kB
pdf PDF
sir2015-5055_table09.xlsx

File Size:37kB
pdf PDF
sir2015-5055_table10.xlsx

File Size:41kB

Abstract

Traditionally, the Iowa Department of Transportation has used the Iowa Runoff Chart and single-variable regional-regression equations (RREs) from a U.S. Geological Survey report (published in 1987) as the primary methods to estimate annual exceedance-probability discharge (AEPD) for small (20 square miles or less) drainage basins in Iowa. With the publication of new multi- and single-variable RREs by the U.S. Geological Survey (published in 2013), the Iowa Department of Transportation needs to determine which methods of AEPD estimation provide the best accuracy and the least bias for small drainage basins in Iowa. Twenty five streamgages with drainage areas less than 2 square miles (mi2) and 55 streamgages with drainage areas between 2 and 20 mi2 were selected for the comparisons that used two evaluation metrics. Estimates of AEPDs calculated for the streamgages using the expected moments algorithm/multiple Grubbs-Beck test analysis method were compared to estimates of AEPDs calculated from the 2013 multivariable RREs; the 2013 single-variable RREs; the 1987 single-variable RREs; the TR-55 rainfall-runoff model; and the Iowa Runoff Chart. For the 25 streamgages with drainage areas less than 2 mi2, results of the comparisons seem to indicate the best overall accuracy and the least bias may be achieved by using the TR-55 method for flood regions 1 and 3 (published in 2013) and by using the 1987 single-variable RREs for flood region 2 (published in 2013). For drainage basins with areas between 2 and 20 mi2, results of the comparisons seem to indicate the best overall accuracy and the least bias may be achieved by using the 1987 single-variable RREs for the Southern Iowa Drift Plain landform region and for flood region 3 (published in 2013), by using the 2013 multivariable RREs for the Iowan Surface landform region, and by using the 2013 or 1987 single-variable RREs for flood region 2 (published in 2013). For all other landform or flood regions in Iowa, use of the 2013 single-variable RREs may provide the best overall accuracy and the least bias. An examination was conducted to understand why the 1987 single-variable RREs seem to provide better accuracy and less bias than either of the 2013 multi- or single-variable RREs. A comparison of 1-percent annual exceedance-probability regression lines for hydrologic regions 1–4 from the 1987 single-variable RREs and for flood regions 1–3 from the 2013 single-variable RREs indicates that the 1987 single-variable regional-regression lines generally have steeper slopes and lower discharges when compared to 2013 single-variable regional-regression lines for corresponding areas of Iowa. The combination of the definition of hydrologic regions, the lower discharges, and the steeper slopes of regression lines associated with the 1987 single-variable RREs seem to provide better accuracy and less bias when compared to the 2013 multi- or single-variable RREs; better accuracy and less bias was determined particularly for drainage areas less than 2 mi2, and also for some drainage areas between 2 and 20 mi2. The 2013 multi- and single-variable RREs are considered to provide better accuracy and less bias for larger drainage areas. Results of this study indicate that additional research is needed to address the curvilinear relation between drainage area and AEPDs for areas of Iowa.

Item Type: Departmental Report
Note: Attached to this record are the 50-page Final Report, the 2-page Technical Brief, and 5 spreadsheets of table data for tables 3, 4, 8, 9, and 10. The brief and spreadsheets are not deposited separately. Suggested citation and DOI link: Eash, D.A., 2015, Comparisons of estimates of annual exceedance-probability discharges for small drainage basins in Iowa, based on data through water year 2013: U.S. Geological Survey Scientific Investigations Report 2015–5055, 37 p., http://dx.doi.org/10.3133/sir20155055
Keywords: Algorithms, Drainage basins, Floods, Stream gages, peak flows
Subjects: Transportation
Transportation > Environment
Transportation > Environment > Water
Natural Disasters > Flood
ID Code: 20467
Deposited By: Leighton Christiansen
Deposited On: 29 Sep 2015 12:10
Last Modified: 29 Sep 2015 12:10
URI: http://publications.iowa.gov/id/eprint/20467