Determining the ecological water allocation in a hyper-arid catchment with increasing competition for water resources

Meeting ecological water requirement adequately plays a significant role in guaranteeing the stability of river basin ecosystems in arid lands. The amounts of water leaked through the riverbed and drawn by ecological brakes in Tarim River were ascertained. Based on data related to soil, hydrology, and vegetation of the river basin, the aims of this paper are to 1) analyse the variation in the size of soil particles and in hydraulic conductivity of four sections of the river; 2) calculate the amount of water that leaked from the riverbed and the percentage of ecological water requirement that can be guaranteed at different frequencies of water inflow; and 3) recommend - using a combination of particle size analysis, Darcy's Law, and GIS - the amount of water to be drawn from ecological brakes along both banks of the river for meeting ecological water requirement adequately. The results showed that 1) the size of soil particles in the riverbed ranged from 1.6 μm to 98.9 μm; 2) hydraulic conductivity followed the normal distribution from year to year but varied in spatial terms, that is across different section of the river; 3) riverbed leakage varied with water frequencies, being 11.36 × 108 m3, 10.62 × 108 m3, 9.84 × 108 m3, 9.32 × 108 m3, and 8.87 × 108 m3 at the frequencies of 10%, 25%, 50%, 75%, and 90%, respectively; 4) the distance over which the leakage contributed to meeting ecological water requirement in the south bank was greater than or equal to the distance in the north bank; and 5) water drawn from ecological brakes on the north bank exceeded that drawn from the brakes on the south bank by 10.89 × 108 m3-11.28 × 108 m3. Ecological water requirement of the desert riparian vegetation was met mainly from riverbed leakage in the south and by drawing from ecological brakes in the north. The present research not only offers a scientific method that could be used for developing suitable schemes for meeting ecological water requirement but also provides a technical guide on running ecological brakes and achieving the optimal allocation of water resources in Tarim River Basin.