George Garklavs Kevin A. Oberg Julia B. Graf 1982 <p>Values of the unit hydrograph parameters time of concentration (<i>TC</i>) and storage coefficient (<i>R</i>) can be estimated for streams in Illinois by a two-step technique developed from data for 98 gaged basins in the State. The sum of <i>TC</i> and <i>R</i> is related to stream length (<i>L</i>) and main channel slope (<i>S</i>) by the relation (<i>TC</i> + <i>R</i>)<i>_e</i> = 35.2<i>L</i>^0.39&nbsp;<i>S</i>^-0.78. The variable <i>R</i>/(<i>TC</i> + <i>R</i>) is not significantly correlated with drainage area, slope, or length, but does exhibit a regional trend. Regional values of <i>R</i>/(<i>TC</i> + <i>R</i>) are used with the computed values of (<i>TC</i> + <i>R</i>)_<i>e</i> to solve for estimated values of time of concentration (<i>TC_e</i>) and storage coefficient (<i>R_e</i>). The use of the variable <i>R</i>/(<i>TC</i> + <i>R</i>) is thought to account for variations in unit hydrograph parameters caused by physiographic variables such as basin topography, flood-plain development, and basin storage characteristics.</p> application/pdf 10.3133/wri8222 en U.S. Geological Survey A technique for estimating time of concentration and storage coefficient values for Illinois streams reports