Hydrological assessment of some old dams in Saudi Arabia under the current climate, environmental conditions, and the use of the advanced technology

Dams were built in Saudi Arabia (SA) starting from the late fifties. The rainfall record at that time is rather short since the early rainfall records in the study area were in the mid-sixties. Therefore, due to the recent changes in climatic conditions worldwide and having longer rainfall records nowadays, it is very important to assess the existing dams under the current conditions. The assessment is based on some criteria: the length of the rainfall records, the rainfall storm hyetographs, storm duration, the type of the rainfall frequency distribution, topographic data, and the current land use/land cover conditions. Fourteen dams in the Riyadh region are chosen, as a pilot study, to perform the proposed dam evaluation procedure. Later, the study can be extended to any region in SA. The results show that increasing the record length leads to a convergence of the rainfall to an asymptotic value. The minimum record length to produce stable statistical rainfall is about 20 years. Nine out of fourteen dams have a storage capacity less than the 5-year return period. The statistical analysis showed that the measured rainfall in some past years corresponds to 50 and 100 years return periods. Gumbel Type I distribution, which was used in the analysis of the old dams, does not seem to be the best distribution under the recent climate data. The dams should also be assessed under the effects of climate change and urban expansion.