Geology topics

David A. Eash

Publications and source records attributed to David A. Eash.

At least 19 recordsLinked to original sources

USGS2018

Stream-channel and watershed delineations and basin-characteristic measurements using lidar elevation data for small drainage basins within the Des Moines Lobe landform region in Iowa

Basin-characteristic measurements related to stream length, stream slope, stream density, and stream order have been identified as significant variables for estimation of flood, flow-duration, and low-flow discharges in Iowa. The placement of channel initiation points, however, has always been a matter of individual interpretation, leading to differences in stream definitions between analysts. This study investigated five different methods to define stream initiation using 3-meter light detection and ranging (lidar) digital elevation models (DEMs) data for 17 streamgages with drainage areas less than 50 square miles within the Des Moines Lobe landform region in north-central Iowa. Each DEM was hydrologically enforced and the five stream initiation methods were used to define channel initiation points and the downstream flow paths. The five different methods to define stream initiation were tested side-by-side for three watershed delineations: (1) the total drainage-area delineation, (2) an effective drainage-area delineation of basins based on a 2-percent annual exceedance probability (AEP) 12-hour rainfall, and (3) an effective drainage-area delineation based on a 20-percent AEP 12-hour rainfall. Generalized least squares regression analysis was used to develop a set of equations for sites in the Des Moines Lobe landform region for estimating discharges for ungaged stream sites with 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent AEPs. A total of 17 streamgages were included in the development of the regression equations. In addition, geographic information system software was used to measure 58 selected basin-characteristics for each streamgage. Results of the regression analyses of the 15 lidar datasets indicate that the datasets that produce regional regression equations (RREs) with the best overall predictive accuracy are the National Hydrographic Dataset, Iowa Department of Natural Resources, and profile curvature of 0.5 stream initiation methods combined with the 20-percent AEP 12-hour rainfall watershed delineation method. These RREs have a mean average standard error of prediction (SEP) for 4-, 2-, and 1-percent AEP discharges of 53.9 percent and a mean SEP for all eight AEPs of 55.5 percent. Compared to the RREs developed in this study using the basin characteristics from the U.S. Geological Survey StreamStats application, the lidar basin characteristics provide better overall predictive accuracy.

Iowa↗

USGS2017

Methods for estimating selected low-flow frequency statistics and harmonic mean flows for streams in Iowa

A statewide study was conducted to develop regression equations for estimating six selected low-flow frequency statistics and harmonic mean flows for ungaged stream sites in Iowa. The estimation equations developed for the six low-flow frequency statistics include: the annual 1-, 7-, and 30-day mean low flows for a recurrence interval of 10 years, the annual 30-day mean low flow for a recurrence interval of 5 years, and the seasonal (October 1 through December 31) 1- and 7-day mean low flows for a recurrence interval of 10 years. Estimation equations also were developed for the harmonic-mean-flow statistic. Estimates of these seven selected statistics are provided for 208 U.S. Geological Survey continuous-record streamgages using data through September 30, 2006. The study area comprises streamgages located within Iowa and 50 miles beyond the State's borders. Because trend analyses indicated statistically significant positive trends when considering the entire period of record for the majority of the streamgages, the longest, most recent period of record without a significant trend was determined for each streamgage for use in the study. The median number of years of record used to compute each of these seven selected statistics was 35. Geographic information system software was used to measure 54 selected basin characteristics for each streamgage. Following the removal of two streamgages from the initial data set, data collected for 206 streamgages were compiled to investigate three approaches for regionalization of the seven selected statistics. Regionalization, a process using statistical regression analysis, provides a relation for efficiently transferring information from a group of streamgages in a region to ungaged sites in the region. The three regionalization approaches tested included statewide, regional, and region-of-influence regressions. For the regional regression, the study area was divided into three low-flow regions on the basis of hydrologic characteristics, landform regions, and soil regions. A comparison of root mean square errors and average standard errors of prediction for the statewide, regional, and region-of-influence regressions determined that the regional regression provided the best estimates of the seven selected statistics at ungaged sites in Iowa. Because a significant number of streams in Iowa reach zero flow as their minimum flow during low-flow years, four different types of regression analyses were used: left-censored, logistic, generalized-least-squares, and weighted-least-squares regression. A total of 192 streamgages were included in the development of 27 regression equations for the three low-flow regions. For the northeast and northwest regions, a censoring threshold was used to develop 12 left-censored regression equations to estimate the 6 low-flow frequency statistics for each region. For the southern region a total of 12 regression equations were developed; 6 logistic regression equations were developed to estimate the probability of zero flow for the 6 low-flow frequency statistics and 6 generalized least-squares regression equations were developed to estimate the 6 low-flow frequency statistics, if nonzero flow is estimated first by use of the logistic equations. A weighted-least-squares regression equation was developed for each region to estimate the harmonic-mean-flow statistic. Average standard errors of estimate for the left-censored equations for the northeast region range from 64.7 to 88.1 percent and for the northwest region range from 85.8 to 111.8 percent. Misclassification percentages for the logistic equations for the southern region range from 5.6 to 14.0 percent. Average standard errors of prediction for generalized least-squares equations for the southern region range from 71.7 to 98.9 percent and pseudo coefficients of determination for the generalized-least-squares equations range from 87.7 to 91.8 percent. Average standard errors of prediction for weighted-least-squares equations developed for estimating the harmonic-mean-flow statistic for each of the three regions range from 66.4 to 80.4 percent. The regression equations are applicable only to stream sites in Iowa with low flows not significantly affected by regulation, diversion, or urbanization and with basin characteristics within the range of those used to develop the equations. If the equations are used at ungaged sites on regulated streams, or on streams affected by water-supply and agricultural withdrawals, then the estimates will need to be adjusted by the amount of regulation or withdrawal to estimate the actual flow conditions if that is of interest. Caution is advised when applying the equations for basins with characteristics near the applicable limits of the equations and for basins located in karst topography. A test of two drainage-area ratio methods using 31 pairs of streamgages, for the annual 7-day mean low-flow statistic for a recurrence interval of 10 years, indicates a weighted drainage-area ratio method provides better estimates than regional regression equations for an ungaged site on a gaged stream in Iowa when the drainage-area ratio is between 0.5 and 1.4. These regression equations will be implemented within the U.S. Geological Survey StreamStats web-based geographic-information-system tool. StreamStats allows users to click on any ungaged site on a river and compute estimates of the seven selected statistics; in addition, 90-percent prediction intervals and the measured basin characteristics for the ungaged sites also are provided. StreamStats also allows users to click on any streamgage in Iowa and estimates computed for these seven selected statistics are provided for the streamgage.

Iowa↗

USGS2016

Methods for estimating selected spring and fall low-flow frequency statistics for ungaged stream sites in Iowa, based on data through June 2014

A statewide study was led to develop regression equations for estimating three selected spring and three selected fall low-flow frequency statistics for ungaged stream sites in Iowa. The estimation equations developed for the six low-flow frequency statistics include spring (April through June) 1-, 7-, and 30-day mean low flows for a recurrence interval of 10 years and fall (October through December) 1-, 7-, and 30-day mean low flows for a recurrence interval of 10 years. Estimates of the three selected spring statistics are provided for 241 U.S. Geological Survey continuous-record streamgages, and estimates of the three selected fall statistics are provided for 238 of these streamgages, using data through June 2014. Because only 9 years of fall streamflow record were available, three streamgages included in the development of the spring regression equations were not included in the development of the fall regression equations. Because of regulation, diversion, or urbanization, 30 of the 241 streamgages were not included in the development of the regression equations. The study area includes Iowa and adjacent areas within 50 miles of the Iowa border. Because trend analyses indicated statistically significant positive trends when considering the period of record for most of the streamgages, the longest, most recent period of record without a significant trend was determined for each streamgage for use in the study. Geographic information system software was used to measure 63 selected basin characteristics for each of the 211streamgages used to develop the regional regression equations. The study area was divided into three low-flow regions that were defined in a previous study for the development of regional regression equations. Because several streamgages included in the development of regional regression equations have estimates of zero flow calculated from observed streamflow for selected spring and fall low-flow frequency statistics, the final equations for the three low-flow regions were developed using two types of regression analyses—left-censored and generalized-least-squares regression analyses. A total of 211 streamgages were included in the development of nine spring regression equations—three equations for each of the three low-flow regions. A total of 208 streamgages were included in the development of nine fall regression equations—three equations for each of the three low-flow regions. A censoring threshold was used to develop 15 left-censored regression equations to estimate the three fall low-flow frequency statistics for each of the three low-flow regions and to estimate the three spring low-flow frequency statistics for the southern and northwest regions. For the northeast region, generalized-least-squares regression was used to develop three equations to estimate the three spring low-flow frequency statistics. For the northeast region, average standard errors of prediction range from 32.4 to 48.4 percent for the spring equations and average standard errors of estimate range from 56.4 to 73.8 percent for the fall equations. For the northwest region, average standard errors of estimate range from 58.9 to 62.1 percent for the spring equations and from 83.2 to 109.4 percent for the fall equations. For the southern region, average standard errors of estimate range from 43.2 to 64.0 percent for the spring equations and from 78.1 to 78.7 percent for the fall equations. The regression equations are applicable only to stream sites in Iowa with low flows not substantially affected by regulation, diversion, or urbanization and with basin characteristics within the range of those used to develop the equations. The regression equations will be implemented within the U.S. Geological Survey StreamStats Web-based geographic information system application. StreamStats allows users to click on any ungaged stream site and compute estimates of the six selected spring and fall low-flow statistics; in addition, 90-percent prediction intervals and the measured basin characteristics for the ungaged site are provided. StreamStats also allows users to click on any Iowa streamgage to obtain computed estimates for the six selected spring and fall low-flow statistics.

Iowa↗

USGS2016

Statistical summaries of selected Iowa streamflow data through September 2013

Statistical summaries of streamflow data collected at 184 streamgages in Iowa are presented in this report. All streamgages included for analysis have at least 10 years of continuous record collected before or through September 2013. This report is an update to two previously published reports that presented statistical summaries of selected Iowa streamflow data through September 1988 and September 1996. The statistical summaries include (1) monthly and annual flow durations, (2) annual exceedance probabilities of instantaneous peak discharges (flood frequencies), (3) annual exceedance probabilities of high discharges, and (4) annual nonexceedance probabilities of low discharges and seasonal low discharges. Also presented for each streamgage are graphs of the annual mean discharges, mean annual mean discharges, 50-percent annual flow-duration discharges (median flows), harmonic mean flows, mean daily mean discharges, and flow-duration curves. Two sets of statistical summaries are presented for each streamgage, which include (1) long-term statistics for the entire period of streamflow record and (2) recent-term statistics for or during the 30-year period of record from 1984 to 2013. The recent-term statistics are only calculated for streamgages with streamflow records pre-dating the 1984 water year and with at least 10 years of record during 1984–2013. The streamflow statistics in this report are not adjusted for the effects of water use; although some of this water is used consumptively, most of it is returned to the streams.

Iowa↗

USGS2015

Evaluation of statistical and rainfall-runoff models for predicting historical daily streamflow time series in the Des Moines and Iowa River watersheds

Daily records of streamflow are essential to understanding hydrologic systems and managing the interactions between human and natural systems. Many watersheds and locations lack streamgages to provide accurate and reliable records of daily streamflow. In such ungaged watersheds, statistical tools and rainfall-runoff models are used to estimate daily streamflow. Previous work compared 19 different techniques for predicting daily streamflow records in the southeastern United States. Here, five of the better-performing methods are compared in a different hydroclimatic region of the United States, in Iowa. The methods fall into three classes: (1) drainage-area ratio methods, (2) nonlinear spatial interpolations using flow duration curves, and (3) mechanistic rainfall-runoff models. The first two classes are each applied with nearest-neighbor and map-correlated index streamgages. Using a threefold validation and robust rank-based evaluation, the methods are assessed for overall goodness of fit of the hydrograph of daily streamflow, the ability to reproduce a daily, no-fail storage-yield curve, and the ability to reproduce key streamflow statistics. As in the Southeast study, a nonlinear spatial interpolation of daily streamflow using flow duration curves is found to be a method with the best predictive accuracy. Comparisons with previous work in Iowa show that the accuracy of mechanistic models with at-site calibration is substantially degraded in the ungaged framework.

Iowa, Minnesota↗

USGS2015

Comparisons of estimates of annual exceedance-probability discharges for small drainage basins in Iowa, based on data through water year 2013

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 (mi 2 ) and 55 streamgages with drainage areas between 2 and 20 mi 2 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 mi 2 , 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 mi 2 , 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 mi 2 , and also for some drainage areas between 2 and 20 mi 2 . 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.

Iowa↗

USGS2014

Summary of U.S. Geological Survey reports documenting flood profiles of streams in Iowa, 1963-2012

This report is part of an ongoing program that is publishing flood profiles of streams in Iowa. The program is managed by the U.S. Geological Survey in cooperation with the Iowa Department of Transportation and the Iowa Highway Research Board (Project HR-140). Information from flood profiles is used by engineers to analyze and design bridges, culverts, and roadways. This report summarizes 47 U.S. Geological Survey flood-profile reports that were published for streams in Iowa during a 50-year period from 1963 to 2012. Flood events profiled in the reports range from 1903 to 2010. Streams in Iowa that have been selected for the preparation of flood-profile reports typically have drainage areas of 100 square miles or greater, and the documented flood events have annual exceedance probabilities of less than 2 to 4 percent. This report summarizes flood-profile measurements, changes in flood-profile report content throughout the years, streams that were profiled in the reports, the occurrence of flood events profiled, and annual exceedance-probability estimates of observed flood events. To develop flood profiles for selected flood events for selected stream reaches, the U.S. Geological Survey measured high-water marks and river miles at selected locations. A total of 94 stream reaches have been profiled in U.S. Geological Survey flood-profile reports. Three rivers in Iowa have been profiled along the same stream reach for five different flood events and six rivers in Iowa have been profiled along the same stream reach for four different flood events. Floods were profiled for June flood events for 18 different years, followed by July flood events for 13 years, May flood events for 11 years, and April flood events for 9 years. Most of the flood-profile reports include estimates of annual exceedance probabilities of observed flood events at streamgages located along profiled stream reaches. Comparisons of 179 historic and updated annual exceedance-probability estimates indicate few differences that are considered substantial between the historic and updated estimates for the observed flood events. Overall, precise comparisons for 114 observed flood events indicate that updated annual exceedance probabilities have increased for most of the observed flood events compared to the historic annual exceedance probabilities. Multiple large flood events exceeding the 2-percent annual exceedance-probability discharge estimate occurred at 37 of 98 selected streamgages during 1960–2012. Five large flood events were recorded at two streamgages in Ames during 1990–2010 and four large flood events were recorded at four other streamgages during 1973–2010. Results of Kendall’s tau trend-analysis tests for 35 of 37 selected streamgages indicate that a statistically significant trend is not evident for the 1963–2012 period of record; nor is an overall clear positive or negative trend evident for the 37 streamgages.

Iowa↗

USGS2013

Methods for estimating annual exceedance-probability discharges for streams in Iowa, based on data through water year 2010

A statewide study was performed to develop regional regression equations for estimating selected annual exceedance-probability statistics for ungaged stream sites in Iowa. The study area comprises streamgages located within Iowa and 50 miles beyond the State’s borders. Annual exceedance-probability estimates were computed for 518 streamgages by using the expected moments algorithm to fit a Pearson Type III distribution to the logarithms of annual peak discharges for each streamgage using annual peak-discharge data through 2010. The estimation of the selected statistics included a Bayesian weighted least-squares/generalized least-squares regression analysis to update regional skew coefficients for the 518 streamgages. Low-outlier and historic information were incorporated into the annual exceedance-probability analyses, and a generalized Grubbs-Beck test was used to detect multiple potentially influential low flows. Also, geographic information system software was used to measure 59 selected basin characteristics for each streamgage. Regional regression analysis, using generalized least-squares regression, was used to develop a set of equations for each flood region in Iowa for estimating discharges for ungaged stream sites with 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities, which are equivalent to annual flood-frequency recurrence intervals of 2, 5, 10, 25, 50, 100, 200, and 500 years, respectively. A total of 394 streamgages were included in the development of regional regression equations for three flood regions (regions 1, 2, and 3) that were defined for Iowa based on landform regions and soil regions. Average standard errors of prediction range from 31.8 to 45.2 percent for flood region 1, 19.4 to 46.8 percent for flood region 2, and 26.5 to 43.1 percent for flood region 3. The pseudo coefficients of determination for the generalized least-squares equations range from 90.8 to 96.2 percent for flood region 1, 91.5 to 97.9 percent for flood region 2, and 92.4 to 96.0 percent for flood region 3. The regression equations are applicable only to stream sites in Iowa with flows not significantly affected by regulation, diversion, channelization, backwater, or urbanization and with basin characteristics within the range of those used to develop the equations. These regression equations will be implemented within the U.S. Geological Survey StreamStats Web-based geographic information system tool. StreamStats allows users to click on any ungaged site on a river and compute estimates of the eight selected statistics; in addition, 90-percent prediction intervals and the measured basin characteristics for the ungaged sites also are provided by the Web-based tool. StreamStats also allows users to click on any streamgage in Iowa and estimates computed for these eight selected statistics are provided for the streamgage.

Iowa↗

USGS2012

Bayesian WLS/GLS regression for regional skewness analysis for regions with large crest stage gage networks

This paper summarizes methodological advances in regional log-space skewness analyses that support flood-frequency analysis with the log Pearson Type III (LP3) distribution. A Bayesian Weighted Least Squares/Generalized Least Squares (B-WLS/B-GLS) methodology that relates observed skewness coefficient estimators to basin characteristics in conjunction with diagnostic statistics represents an extension of the previously developed B-GLS methodology. B-WLS/B-GLS has been shown to be effective in two California studies. B-WLS/B-GLS uses B-WLS to generate stable estimators of model parameters and B-GLS to estimate the precision of those B-WLS regression parameters, as well as the precision of the model. The study described here employs this methodology to develop a regional skewness model for the State of Iowa. To provide cost effective peak-flow data for smaller drainage basins in Iowa, the U.S. Geological Survey operates a large network of crest stage gages (CSGs) that only record flow values above an identified recording threshold (thus producing a censored data record). CSGs are different from continuous-record gages, which record almost all flow values and have been used in previous B-GLS and B-WLS/B-GLS regional skewness studies. The complexity of analyzing a large CSG network is addressed by using the B-WLS/B-GLS framework along with the Expected Moments Algorithm (EMA). Because EMA allows for the censoring of low outliers, as well as the use of estimated interval discharges for missing, censored, and historic data, it complicates the calculations of effective record length (and effective concurrent record length) used to describe the precision of sample estimators because the peak discharges are no longer solely represented by single values. Thus new record length calculations were developed. The regional skewness analysis for the State of Iowa illustrates the value of the new B-WLS/BGLS methodology with these new extensions.

Conference Paper↗

USGS2012

Floods of July 23-26, 2010, in the Little Maquoketa River and Maquoketa River Basins, Northeast Iowa

Minor flooding occurred July 23, 2010, in the Little Maquoketa River Basin and major flooding occurred July 23–26, 2010, in the Maquoketa River Basin in northeast Iowa following severe thunderstorm activity over the region during July 22–24. A breach of the Lake Delhi Dam on July 24 aggravated flooding on the Maquoketa River. Rain gages at Manchester and Strawberry Point, Iowa, recorded 72-hour-rainfall amounts of 7.33 and 12.23 inches, respectively, on July 24. The majority of the rainfall occurred during a 48-hour period. Within the Little Maquoketa River Basin, a peak-discharge estimate of 19,000 cubic feet per second (annual flood-probability estimate of 4 to 10 percent) at the discontinued 05414500 Little Maquoketa River near Durango, Iowa streamgage on July 23 is the sixth largest flood on record. Within the Maquoketa River Basin, peak discharges of 26,600 cubic feet per second (annual flood-probability estimate of 0.2 to 1 percent) at the 05416900 Maquoketa River at Manchester, Iowa streamgage on July 24, and of 25,000 cubic feet per second (annual flood-probability estimate of 1 to 2 percent) at the 05418400 North Fork Maquoketa River near Fulton, Iowa streamgage on July 24 are the largest floods on record for these sites. A peak discharge affected by the Lake Delhi Dam breach on July 24 at the 05418500 Maquoketa River near Maquoketa, Iowa streamgage, located downstream of Lake Delhi, of 46,000 cubic feet per second on July 26 is the third highest on record. High-water marks were measured at five locations along the Little Maquoketa and North Fork Little Maquoketa Rivers between U.S. Highway 52 near Dubuque and County Road Y21 near Rickardsville, a distance of 19 river miles. Highwater marks were measured at 28 locations along the Maquoketa River between U.S. Highway 52 near Green Island and State Highway 187 near Arlington, a distance of 142 river miles. High-water marks were measured at 13 locations along the North Fork Maquoketa River between Rockdale Road near Maquoketa and U.S. Highway 52 near Luxemburg, a distance of 90 river miles. The high-water marks were used to develop flood profiles for the Little Maquoketa, North Fork Little Maquoketa, Maquoketa, and North Fork Maquoketa Rivers.

Iowa↗

USGS2012

Flood of August 11–16, 2010, in the South Skunk River Basin, central and southeast Iowa

Severe thunderstorm activity during August 8–11, 2010 in central and southeast Iowa resulted in major flooding from August 11–16, 2010, in the South Skunk River Basin. Rain gages at Ames and Story City recorded 96-hour rainfall amounts of 9.61 and 8.70 inches, respectively. The majority of the rainfall occurred during a 52-hour period, beginning late at night on August 8. Within the South Skunk River Basin, peak discharges of 14,800 cubic feet per second (annual flood-probability estimate of 0.2 to 1 percent) at the 05470000 South Skunk River near Ames, Iowa streamgage; of 36,200 cubic feet per second (annual flood-probability estimate of less than 0.2 percent) at the 05471000 South Skunk River below Squaw Creek near Ames, Iowa streamgage (both on August 11, 2010); and of 24,000 cubic feet per second (annual flood-probability estimate of 0.2 to 1 percent) at 05471050 South Skunk River at Colfax, Iowa streamgage on August 14 are the largest floods on record for these sites. Peak discharges at 05470500 Squaw Creek at Ames, Iowa streamgage of 22,400 cubic feet per second (annual flood-probability estimate of less than 0.2 percent) on August 11; and at 05471500 South Skunk River near Oskaloosa, Iowa streamgage, of 25,200 cubic feet per second (annual flood- probability estimate of 1 to 2 percent) on August 16 are the second highest floods on record. This report provides a description of the watershed, the thunderstorms, the flooding, and a profile of high-water marks measured at 20 locations along the South Skunk River between County Road V67/280th Avenue, northeast of Ollie in Keokuk County and West Riverside Road in Ames, a distance of 128 river miles.

Iowa↗

USGS2010

Flood of June 8-9, 2008, Upper Iowa River, Northeast Iowa

Major flooding occurred June 8-9, 2008, in the Upper Iowa River Basin in northeast Iowa following severe thunderstorm activity over the region. About 7 inches of rain were recorded for the 48-hour period ending 4 p.m., June 8, at Decorah, Iowa; more than 7 inches of rain were recorded for the 48-hour period ending 7 a.m., June 8, at Dorchester, Iowa, about 17 miles northeast of Decorah. The maximum peak discharge measured in the Upper Iowa River was 34,100 cubic feet per second at streamgage 05387500 Upper Iowa River at Decorah, Iowa. This discharge is the largest discharge recorded in the Upper Iowa River Basin since streamgaging operations began in the basin in 1914. The flood-probability range of the peak discharge is 0.2 to 1 percent. High-water marks were measured at 15 locations along the Upper Iowa River between State Highway 26 near the mouth at the Mississippi River and U.S. Highway 63 at Chester, Iowa, a distance of 124 river miles. The high-water marks were used to develop a flood profile.

Open-File Report↗

USGS2010

Floods of May and June 2008 in Iowa

An unusually wet winter and spring of 2007 to 2008 resulted in extremely wet antecedent conditions throughout most of Iowa. Rainfall of 5 to 15 inches was observed in eastern Iowa during May 2008, and an additional 5 to 15 inches of rain was observed throughout most of Iowa in June. Because of the severity of the May and June 2008 flooding, the U.S. Geological Survey, in cooperation with other Federal, State, and local agencies, has summarized the meteorological and hydrological conditions leading to the flooding, compiled flood-peak stages and discharges, and estimated revised flood probabilities for 62 selected streamgages. Record peak discharges or flood probabilities of 1 percent or smaller (100-year flooding or greater) occurred at more than 60 streamgage locations, particularly in eastern Iowa. Cedar Rapids, Decorah, Des Moines, Iowa City, Mason City, and Waterloo were among the larger urban areas affected by this flooding. High water and flooding in small, headwater streams in north-central and eastern Iowa, particularly in June, combined and accumulated in large, mainstem rivers and resulted in flooding of historic proportions in the Cedar and Iowa Rivers. Previous flood-peak discharges at many locations were exceeded by substantial amounts, in some cases nearly doubling the previous record peak discharge at locations where more than 100 years of streamflow record are available.

Open-File Report↗

USGS2010

Floods of May 30 to June 15, 2008, in the Iowa River and Cedar River Basins, eastern Iowa

As a result of prolonged and intense periods of rainfall in late May and early June, 2008, along with heavier than normal snowpack the previous winter, record flooding occurred in Iowa in the Iowa River and Cedar River Basins. The storms were part of an exceptionally wet period from May 29 through June 12, when an Iowa statewide average of 9.03 inches of rain fell; the normal statewide average for the same period is 2.45 inches. From May 29 to June 13, the 16-day rainfall totals recorded at rain gages in Iowa Falls and Clutier were 14.00 and 13.83 inches, respectively. Within the Iowa River Basin, peak discharges of 51,000 cubic feet per second (flood-probability estimate of 0.2 to 1 percent) at the 05453100 Iowa River at Marengo, Iowa streamflow-gaging station (streamgage) on June 12, and of 39,900 cubic feet per second (flood-probability estimate of 0.2 to 1 percent) at the 05453520 Iowa River below Coralville Dam near Coralville, Iowa streamgage on June 15 are the largest floods on record for those sites. A peak discharge of 41,100 cubic feet per second (flood-probability estimate of 0.2 to 1 percent) on June 15 at the 05454500 Iowa River at Iowa City, Iowa streamgage is the fourth highest on record, but is the largest flood since regulation by the Coralville Dam began in 1958. Within the Cedar River Basin, the May 30 to June 15, 2008, flood is the largest on record at all six streamgages in Iowa located on the mainstem of the Cedar River and at five streamgages located on the major tributaries. Flood-probability estimates for 10 of these 11 streamgages are less than 1 percent. Peak discharges of 112,000 cubic feet per second (flood-probability estimate of 0.2 to 1 percent) at the 05464000 Cedar River at Waterloo, Iowa streamgage on June 11 and of 140,000 cubic feet per second (flood-probability estimate of less than 0.2 percent) at the 05464500 Cedar River at Cedar Rapids, Iowa streamgage on June 13 are the largest floods on record for those sites. Downstream from the confluence of the Iowa and Cedar Rivers, the peak discharge of 188,000 cubic feet per second (flood-probability estimate of less than 0.2 percent) at the 05465500 Iowa River at Wapello, Iowa streamgage on June 14, 2008, is the largest flood on record in the Iowa River and Cedar River Basins since 1903. High-water marks were measured at 88 locations along the Iowa River between State Highway 99 near Oakville and U.S. Highway 69 in Belmond, a distance of 319 river miles. High-water marks were measured at 127 locations along the Cedar River between Fredonia near the mouth (confluence with the Iowa River) and Riverview Drive north of Charles City, a distance of 236 river miles. The high-water marks were used to develop flood profiles for the Iowa and Cedar River.

Iowa↗

USGS2009

Basinsoft, a computer program to quantify drainage basin characteristics

Surface water runoff is a function of many interrelated factors including climate, soils, landuse, and the physiography of the drainage basin. A practical and effective method to quantify drainage basin characteristics would allow analysis of the interrelations of these factors, leading to an improved understanding of the effects of drainage basin characteristics on surface-water runoff. Historically, the quantification of drainage basin characteristics has been a tedious and time-consuming process. Recent improvements in computer hardware and software technology have enabled the developers of a program called Basinsoft to automate this process. Basinsoft requires minimal preprocessing of data and provides an efficient, automated procedure for quantifying selected morphometric characteristics and the option to area-weight characteristics for a drainage basin. The user of Basinsoft is assumed to have a limited amount of experience in the use of ARC/INFO, a proprietary geographic information system (GIS). (The use of brand names in this chapter is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey [USGS].) In 1988, the USGS began developing a program called Basinsoft. The initial program quantified 16 selected drainage basin characteristics from three source-data layers that were manually digitized from topographic maps using the versions of ARC/INFO, Fortran programs, and prime system Command Programming Language (CPL) programs available in 1988 (Majure and Soenksen, 1991). By 1991, Basinsoft was enhanced to quantify 27 selected drainage-basin characteristics from three source-data layers automatically generated from digital elevation model (DEM) data using a set of Fortran programs (Majure and Eash, 1991: Jenson and Dominique, 1988). Due to edge-matching problems encountered in 1991 with the preprocessing

Book chapter↗

USGS2008

Flood of May 6, 2007, Willow Creek, west-central Iowa

Major flooding occurred May 6, 2007, in the Willow Creek drainage basin in Harrison County following severe thunderstorm activity over west-central Iowa. More than 7 inches of rain were recorded for the 72-hour period ending 7 a.m., May 6, at the Logan, Iowa weather station. The peak discharge in Willow Creek at Medford Avenue near Missouri Valley, Iowa, was 17,000 cubic feet per second. The recurrence interval of the flood is 160 years, which was estimated using regional regression equations. Information about the basin, the storms, the flooding, and a profile of high-water marks measured at 10 locations along Willow Creek between the mouth at the Boyer River and State Highway 37 in Monona County, a distance of almost 33 river miles, are presented in this report.

Iowa↗

USGS2008

Flood-plain study of the Upper Iowa River in the vicinity of Decorah, Iowa

The city of Decorah, Iowa, has experienced severe flooding from the Upper Iowa River resulting in property damage to homes and businesses. Streamflow data from two U.S. Geological Survey (USGS) streamflow-gaging stations, the Upper Iowa River at Decorah, Iowa (station number 05387500), located upstream from the College Drive bridge; and the Upper Iowa River near Decorah, Iowa (station number 05388000), at the Clay Hill Road bridge (locally known as the Freeport bridge) were used in the study. The three largest floods on the Upper Iowa River at Decorah occurred in 1941, 1961, and 1993, for which the estimated peak discharges were 27,200 cubic feet per second (ft3/s), 20,200 ft3/s, and 20,500 ft3/s, respectively. Flood-discharge information can be obtained from the World Wide Web at URL (uniform resource locator) http://waterdata.usgs.gov/nwis/ . In response to the need to provide the City of Decorah and other flood-plain managers with an assessment of the risks of flooding to properties and facilities along an 8.5-mile (mi) reach of the Upper Iowa River, the USGS, in cooperation with the City of Decorah, initiated a study to map 100- and 500-year flood-prone areas.

Iowa↗

USGS2007

A Geographic Information System procedure to quantify drainage-basin characteristics

The Basin Characteristics System (BCS) has been developed to quantify characteristics of a drainage basin. The first of four main BCS processing steps creates four geographic information system (GIS) digital maps representing the drainage divide, the drainage network, elevation contours, and the basin length. The drainage divide and basin length are manually digitized from 1:250,000-scale topographic maps. The drainage network is extracted using GIS software from 1:100,000-scale digital line graph data. The elevation contours are generated using GIS software from 1:250,000-scale digital elevation model data. The second and third steps use software developed to assign attributes to specific features in three of the four digital maps and analyze the four maps to quantify 24 morphometric basin characteristics. The fourth step quantifies two climatic characteristics from digitized State maps of precipitation data. Compared to manual methods of measurement, the BCS provides a reduction in the time required to quantify the 26 basin characteristics. Comparison tests indicate the BCS measurements are not significantly different from manual topographic-map measurements for 11 of 12 primary drainage-basin characteristics. Tests indicate the BCS significantly underestimates basin slope. Comparison-measurement differences for basin slope, main channel slope, and basin relief appear to be due to limitations in the digital elevation model data.

Conference Paper↗