The joint probability method of determining the flood return period of a tidally affected pond




In this paper a method is presented to determine the return period of flood levels within detention ponds used to store surface water runoff for affected coastal catchments. A simulation method is proposed in probability space based on derivation of the joint probability of occurrence of pond levels by combining the probability of the rainfall inflow hydrograph and peak tidal amplitudes. Each combination of events is then analyzed and the overall pond level statistics of the site produced. The results are to be used in an attempt to produce a rational approach to the problem of the design of detention ponds in coastal regions. The technique was applied to an existing tidally affected pond in Newport in the United Kingdom that is surcharged at the outlet due to the occurrence of tidal fluctuations. The results prove that traditional design assumptions that the peak inflow occurs at the peak high tide are pessimistic and lead to overdesigned systems