oa Towards development of world-class standards for designing surface water infrastructure in Qatar: Derivation of design rainfalls

The Qatar National Vision (QNV 2030) defined long-term vision of developing a world class and sustainable infrastructure network in Qatar. In order to achieve goals of QNV, Ministry of Municipality and Urban Planning (MMUP) of Qatar has carried out a comprehensive rainfall study for estimation of design rainfall for Qatar. This study is aimed at development of guidelines and standards for the design of storm and surface water infrastructure in Qatar. For design and operation of water infrastructure, erosion control and many other environmental and stormwater management tasks, design rainfall is a fundamental input. The developed countries have spent millions of dollars to derive national standards of design rainfalls, generally known as intensity-duration-frequency (IDF) curves. For Qatar, the old IDF data was developed in 1991 based on a limited data set and basic statistical approaches. Since then there have been significant developments in statistical techniques to derive IDF data and moreover at many locations in Qatar, the length of the observed rainfall data has increased notably. These have given the opportunity to derive new sets of IDF data for Qatar. This paper presents an overview of the derivation of new set of IDF data for Qatar. The adopted approach uses method of L-moments, which reduces the impacts of sampling variability on the analysis. This also adopts index regional frequency approach with the mean rainfall as the scaling factor. The daily rainfall data from 32 stations located in Qatar and nearby Gulf countries has been used to form a homogeneous region based on the criteria of Hosking and Wallis. The application of goodness-of-fit criteria resulted in the selection of the Pearson Type 3 distribution as the best-fit distribution for the 24-hour duration annual maximum rainfall data in the Qatar region. To apply the developed regional method for any arbitrary un-gauged location, a prediction equation is developed where mean annual maximum rainfall is expressed as a function of physiographic characteristics. From a leave-one-out validation approach, it has been found the developed prediction equation can be used to estimate mean annual maximum rainfall with a median relative error of 5.5%. Finally, an empirical approach is used to obtain design rainfalls for other durations due to the limitations of continuous pluviograph data. The newly derived set of IDF curves are based on a larger dataset and more advance statistical techniques than the existing 1991 IDF curves, thus these new IDF data presents a solid scientific basis for stor mwater system design, flood and environmental studies.