Regionalization of Low‐flow Frequency Estimates: An Alabama Case Stui)y¹

Low‐flow estimates, as determined by probabilistic modeling of observed data sequences, are commonly used to describe certain streamflow characteristics. Unfortunately, however, reliable low‐flow estimates can be difficult to come by, particularly for gaging sites with short record lengths. The shortness of records leads to uncertainties not only in the selection of a distribution for modeling purposes but also in the estimates of the parameters of a chosen model. In flood frequency analysis, the common approach to mitigation of some of these problems is through the regionalization of frequency behavior. The same general approach is applied here to the case of low‐flow estimation, with the general intent of not only improving low‐flow estimates but also illustrating the gains that might be attained in so doing. Data used for this study is that which has been systematically observed at 128 streamflow gaging sites across the State of Alabama. Our conclusions are that the log Pearson Type 3 distribution is a suitable candidate for modeling of Alabama low‐flows, and that the shape parameter of that distribution can be estimated on a regional basis. Low‐flow estimates based on the regional estimator are compared with estimates based on the use of only at‐site estimation techniques.