4. CONCLUSIONS
The hydrological data of flash flood events were obtained from the WH
system developed in JRV. The statistical analysis quantified the
correlations among the variables and their probability distributions. A
strong correlation was not found among the variables, implicating that
the spatial rainfall distribution was uneven and that the runoff process
was nonlinear and highly stochastic. Researches on those physical
phenomena shall be conducted in the follow-up studies, but we recommend
direct monitoring of runoff discharges rather than rainfall depths for
practical desing of WH systems. Probability distribution fitting was
successful with LN3 or GEV, and the design of the WH system was
verified. The spillway was designed with a return period of about 12
years but well functioned for the historical flash flood event with a
return period of about 26 years. The design of a spillway based on the
200 years return period might be excessive in the context of
cost-benefit analysis if the failure of the hydraulic structures would
not give rise to significant consequences. The obtained knowledge of
hydrology in JRV will be useful for designing and operating WH systems
in the future.