This study aims to find out variation characteristics of the parameters of ‘a’ and ‘b’ in L=a ·Qb, an empirical equation for run-off loading (L) and flow rate (Q), by evaluating the effects of flow conditions and regional properties of the watersheds on the values. We selected the Kamo River basin (155 km2) as a study field, and conducted various kinds of investigations, such as 80 day high frequency observations, continuous monitoring for more than 2 years, storm event surveys, and simultaneous surveys of 39 stations. Then, we obtained 7–170 data in each of 39 sampling stations. The main results obtained are as follows: 1) L–Q equation with a range of ‘a’ can express L–Q relation in most of the WQIs (water quality indices); 2) ‘a’ receives temporal (flow condition) effects more in SS, VSS and Al, while it receives regional effect more in inorganic carbon, TN, Ca and Fe; 3) both of flow change in storm events, and base flow levels affect the L–Q relation, and their effects can classify the WQIs into several groups; 4) the effects of regional properties were obviously observed in ‘a’, and quantitatively evaluated, especially for density of population.

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