Flow-duration curves for 1968-98 were estimated for 16 ungaged sites in the Cimarron and lower Arkansas River Basins in south-central Kansas. The method of estimation used six unique factors of flow duration: (1) mean streamflow and percentage duration of mean streamflow, (2) ratio of 1-percent-duration streamflow to mean streamflow, (3) ratio of 0.1-percent-duration streamflow to 1-percent-duration streamflow, (4) ratio of 50-percent-duration streamflow to mean streamflow, (5) percentage duration of appreciable streamflow (0.10 cubic foot per second), and (6) average slope of the flow-duration curve. These factors were previously developed from a regionalized study of flow-duration curves using streamflow data for 1921-76. The method was tested on a currently measured, continuous-record streamflow-gaging station on the Little Arkansas River at Valley Center, Kansas, and was found to adequately estimate the computed flow-duration curve for the station. The low-flow parts of the estimated flow-duration curves were improved substantially using low- to medium-flow discharge measurements made concurrently with discharge measurements and flow-duration analyses performed at nearby, long-term, continuous-record, streamflow-gaging stations. The estimated flow-duration curves at the ungaged sites can be used for projecting future flow frequencies for assessment of total maximum daily loads (TMDL's) or other water-quality constituents and for water-availability studies.
