Geology topics
Publications and source records attributed to O. G. Lara.
This report presents stations descriptions and tables of peak stages and discharges for 280 continuous- and partial-record gaging stations in Iowa. Data for the annual flood series for each gaging station and partial-duration series, at stations where available, are contained in the report.
This report provides techniques and procedures for estimating the probable magnitude and frequency of floods at ungaged sites on Iowa streams. Physiographic characteristics were used to define the boundaries of five hydrologic regions. Regional regression equations that relate the size of the drainage area to flood magnitude are defined for estimating peak discharges having specified recurrence intervals of 2, 5, 10, 25, 50, and 100 years. Regional regression equations are applicable to sites on streams that have drainage areas ranging from 0.04- to 5,150 square miles provided that the streams are not affected significantly by regulation upstream from the sites and that the drainage areas upstream from the sites are not mostly urban areas. Flood-frequency characteristics for the mains terns of selected rivers are presented in graphs as a function of drainage area.
Streamflow discharge is usually determined indirectly from measurements of the river stage at gaging stations and through the use of stage-discharge relationships (rating curves). However, in alluvial streams, stage-discharge relationships change continually and, sometimes, quite markedly. Such changes may be caused by major floods, seasonal variations, or long-term secular trends associated with changes in the river channel. Consequently, reliable estimates of discharge using rating curves are not possible unless frequent direct measurements of discharge are made. Such measurements involve appreciable costs, and it is important to evaluate their contribution in increasing the accuracy of estimation of quantities of interest such as mean daily, monthly or annual flow. A methodology for the evaluation of the efficiency of data-collection strategies for alluvial rivers is developed and applied to stations on the Missouri River, U.S.A. A flexible and expedient model describing the variability of discharges and shifts in the stage-discharge relationship is developed. Procedures for the estimation of parameters and the validation of the model using actual data are presented. The calibrated and validated model is then employed in simulations to evaluate the effect of sampling strategies (such as frequency and accuracy of discharge measurements) on the accuracy of estimated mean daily, monthly and annual flow. Curves relating the cost of sampling to the achieved accuracy can be generated, and the optimization of sampling strategies given accuracy or budget objectives or constraints can be achieved.
This report documents the results of a study of the cost-effectiveness of the stream-gaging program in Iowa. Data uses and funding sources were identified for the 122 surface-water stations (including reservoir, lake, stage only, and miscellaneous stations) operated by the U. S. Geological Survey in Iowa. There are 110 continuous streamflow stations currently being operated in Iowa with an annual budget of $592,000. The average standard error of estimation in continuous streamflow records is 11.4 percent. It was shown that this overall degree of accuracy at the 110 continuous streamflow stations could be improved to 10.5 percent if the gaging schedule was optimized. A minimum budget of $543,000 is required to operate the present streamgaging program in Iowa. With this budget, routine visits to gages would be decreased to five during the open-water season and three during the winter. A budget less than this does not permit proper maintenance of the gages and recorders. At the minimum budget, the average standard error would be 12.5 percent. The maximum budget analyzed was $1,235,000, which resulted in an average standard error of 4.2 percent. A 10 percent increase in the current budget to $656,000 would result in a standard error of 8.4 percent. There are still a few basins with drainage areas greater than 200 square miles that have no continuous streamflow data. Continuous streamflow gages need to be established in these basins as funds become available. All stations in the current program need to be maintained for the forseeable future. Data simulated by using the flow-routing and regression methods for stations in 6 river basins do not meet the accuracy required for their data use. Other basins will be studied later to determine if alternative methods to meet accuracy standards are feasible.
No abstract available.