Comparisons of estimates of annual exceedance-probability discharges for small drainage basins in Iowa, based on data through water year 2013
Comparisons of estimates of annual exceedance-probability discharges for small drainage basins in Iowa, based on data through water year 2013
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根据 2013 年水年的数据，对爱荷华州小型流域的年度超标概率流量估算值进行比较
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发表时间：
2015
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通讯作者：
D. Eash
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作者：
D. Eash
传统上，爱荷华州交通部使用美国地质调查局报告（1987年出版）中的爱荷华州径流图和单变量区域回归方程（RRE）作为估算爱荷华州小型（20平方英里或更小）流域年径流概率流量（AEPD）的主要方法。随着美国地质调查局发布新的多变量和单变量RRE（2013年发布），爱荷华州交通部需要确定哪些AEPD估计方法为爱荷华州的小型流域提供最佳准确度和最小偏差。选择了25个流域面积小于2平方英里（mi²）的流量计和55个流域面积在2到20 mi²之间的流量计，用于使用两种评价指标进行比较。将使用预期矩算法/多重Grubbs-Beck检验分析方法计算的流量计AEPD估计值与根据2013年多变量RRE、2013年单变量RRE、1987年单变量RRE、TR-55径流模型和爱荷华州径流图计算的AEPD估计值进行比较。对于流域面积小于2 mi²的25个流量计，比较结果似乎表明，使用TR-55方法（洪水区1和3）（2013年发布）和使用1987年单变量RRE（洪水区2）（2013年发布）可以实现最佳的整体精度和最小偏差。对于面积在2和20平方英里之间的流域，比较结果似乎表明，使用1987年单变量RRE对南爱荷华州漂流平原地貌区和洪水区3可以实现最佳的整体精度和最小的偏差（发表于2013年），通过使用2013年多变量RRE的爱荷华州表面地貌区域，并通过使用2013年或1987年单变量RRE的洪水区域2（发表于2013年）。对于爱荷华州的所有其他地形或洪水地区，使用2013年单变量RRE可能提供最佳的整体准确性和最小的偏差。进行了一项检查，以了解为什么1987年单变量RRE似乎比2013年多变量或单变量RRE提供更好的准确性和更少的偏倚。比较1987年单变量RRE的水文区域1-4和2013年单变量RRE的洪水区域1-3的1%年径流率-概率回归线表明，与爱荷华州相应地区的2013年单变量区域回归线相比，1987年单变量区域回归线通常具有更陡的斜率和更低的流量。与2013年多变量或单变量RRE相比，1987年单变量RRE的水文区域定义、较低的流量和回归线的较陡斜率的组合似乎提供了更好的准确性和更小的偏差;特别是对于小于2平方英里的排水面积，以及对于2至20平方英里的一些排水面积，确定了更好的准确性和更小的偏差。2013年的多变量和单变量RRE被认为提供了更好的准确性和更小的偏差，用于更大的流域面积。这项研究的结果表明，需要额外的研究，以解决排水面积和AEPDs的爱荷华州地区之间的曲线关系。
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.