Effects of urban development on the flood-flow characteristics of the Walnut Creek Basin, Des Moines Metropolitan area, Iowa,1978.

This report deals with the probable impact of urban development on the magnitude and frequency of flooding in the lower reach of the Walnut Creek Basin.

Estimating Design-Flood Discharges for Streams in Iowa Using Drainage-Basin and Channel-Geometry Characteristics, HR-322, 1993

Drainage-basin and channel-geometry multiple-regression equations are presented for estimating design-flood discharges having recurrence intervals of 2, 5, 10, 25, 50, and 100 years at stream sites on rural, unregulated streams in Iowa. Design-flood discharge estimates determined by Pearson Type-III analyses using data collected through the 1990 water year are reported for the 188 streamflow-gaging stations used in either the drainage-basin or channel-geometry regression analyses. Ordinary least-squares multiple-regression techniques were used to identify selected drainage-basin and channel-geometry regions. Weighted least-squares multiple-regression techniques, which account for differences in the variance of flows at different gaging stations and for variable lengths in station records, were used to estimate the regression parameters. Statewide drainage-basin equations were developed from analyses of 164 streamflow-gaging stations. Drainage-basin characteristics were quantified using a geographic-information-system (GIS) procedure to process topographic maps and digital cartographic data. The significant characteristics identified for the drainage-basin equations included contributing drainage area, relative relief, drainage frequency, and 2-year, 24-hour precipitation intensity. The average standard errors of prediction for the drainage-basin equations ranged from 38.6% to 50.2%. The GIS procedure expanded the capability to quantitatively relate drainage-basin characteristics to the magnitude and frequency of floods for stream sites in Iowa and provides a flood-estimation method that is independent of hydrologic regionalization. Statewide and regional channel-geometry regression equations were developed from analyses of 157 streamflow-gaging stations. Channel-geometry characteristics were measured on site and on topographic maps. Statewide and regional channel-geometry regression equations that are dependent on whether a stream has been channelized were developed on the basis of bankfull and active-channel characteristics. The significant channel-geometry characteristics identified for the statewide and regional regression equations included bankfull width and bankfull depth for natural channels unaffected by channelization, and active-channel width for stabilized channels affected by channelization. The average standard errors of prediction ranged from 41.0% to 68.4% for the statewide channel-geometry equations and from 30.3% to 70.0% for the regional channel-geometry equations. Procedures provided for applying the drainage-basin and channel-geometry regression equations depend on whether the design-flood discharge estimate is for a site on an ungaged stream, an ungaged site on a gaged stream, or a gaged site. When both a drainage-basin and a channel-geometry regression-equation estimate are available for a stream site, a procedure is presented for determining a weighted average of the two flood estimates.

Floods of 1986 and 1990 in the Raccoon River Basin, West-Central Iowa, HR-140, 1992

Water-surface-elevation profiles and peak discharges for the floods of 1973 and 1979 are compared to those of 1986 and 1990 in the Raccoon River basin, west-central Iowa. The profiles illustrate the 1979 and 1986 floods on the Raccoon, South Raccoon, and Middle Raccoon Rivers, the 1973 and 1986 floods on Walnut Creek, and the 1986 flood on Willow Creek and Mosquito Creek. The 1986 flood is the largest on record at U.S. Geological Survey streamflowgaging stations on the Middle Raccoon River tributary at Carroll, Middle Raccoon River near Bayard, Middle Raccoon River at Panora, and Walnut Creek at Des Moines. The 1990 flood discharge is the largest on record at U.S. Geological Survey crest-stage gaging stations on Hardin Creek near Farlin and on East Fork Hardin Creek near Churdan. The flood history given in this report describes rainfall conditions for floods that occurred during 1986 and 1990. Discharge for the 1990 flood on East Fork Hardin Creek near Churdan was 1.01 times larger than the 100-year recurrence-interval discharge.

Insights into the Design and Characteristics of the Sedimentation Process at Multi-Barrel Culverts in Iowa, TR-596, 2010

The present study is an integral part of a broader study focused on the design and implementation of self-cleaning culverts, i.e., configurations that prevent the formation of sediment deposits after culvert construction or cleaning. Sediment deposition at culverts is influenced by many factors, including the size and characteristics of material of which the channel is composed, the hydraulic characteristics generated under different hydrology events, the culvert geometry design, channel transition design, and the vegetation around the channel. The multitude of combinations produced by this set of variables makes the investigation of practical situations a complex undertaking. In addition to the considerations above, the field and analytical observations have revealed flow complexities affecting the flow and sediment transport through culverts that further increase the dimensions of the investigation. The flow complexities investigated in this study entail: flow non-uniformity in the areas of transition to and from the culvert, flow unsteadiness due to the flood wave propagation through the channel, and the asynchronous correlation between the flow and sediment hydrographs resulting from storm events. To date, the literature contains no systematic studies on sediment transport through multi-box culverts or investigations on the adverse effects of sediment deposition at culverts. Moreover, there is limited knowledge about the non-uniform, unsteady sediment transport in channels of variable geometry. Furthermore, there are few readily useable (inexpensive and practical) numerical models that can reliably simulate flow and sediment transport in such complex situations. Given the current state of knowledge, the main goal of the present study is to investigate the above flow complexities in order to provide the needed insights for a series of ongoing culvert studies. The research was phased so that field observations were conducted first to understand the culvert behavior in Iowa landscape. Modeling through complementary hydraulic model and numerical experiments was subsequently carried out to gain the practical knowledge for the development of the self-cleaning culvert designs.

Floods in the Nishnabotna River Basin, Iowa, HR-140, 1991

Flood-elevation profiles and flood-peak discharges for floods during 1972, 1982, and 1987 in the Nishnabotna River basin are given in the report. The profiles are for the 1972 flood on the West and East Nishnabotna Rivers, the 1982 flood on Indian Creek, and the 1987 flood on the lower West Nishnabotna River. A flood history describes rainfall conditions and reported damages for floods occurring 1947, 1958, 1972, 1982, and 1987. Discharge for the 1982 flood on Indian Creek is 1.1 times larger than the 100-year recurrence interval discharge.