This paper presents a procedure to derive historical-annual and historical-monthly flow duration curves (FDC) that are monotonic and continuous for agricultural, unregulated, ungauged sites. The authors explore the performance and the regional dependence of four different regression models for the estimation of daily flow quantiles (QpQp), with probabilities of exceedance (pp) ranging from 0.01 to 0.99. The construction and analysis of the four regression models is based on scale-invariance of QpQp with respect to drainage area (AA) or mean annual flow (Q¯Q¯). The authors implemented the procedure using data from 74 gauged sites in the state of Iowa. The study concludes that the multi-scaling framework of QpQp with respect to Q¯Q¯ provides the most accurate FDC estimates, which are region-independent within the physical characteristics of Iowa.

Perez, G., R. Mantilla, and W.F. Krajewski, Estimating annual and monthly scale-invariant flow duration curves for the State of Iowa, Journal of Hydrologic Engineering,23(12): 05018021, 2018.