Critical environmental flows to support integrated ecological objectives for the Yellow River Estuary, China

The volume of inflowing water needed to meet multiple demands in the Yellow River Estuary of China was examined and quantified. Pressure on available environmental flows comes from varied ecological objectives, including maintenance of freshwater habitat for hundreds of plant and animal species, salinity balance, sediment transport and general equilibrium of the hydrologic cycle. Temporal fluctuations of flow input and output were considered and the amount of water needed for both consumptive and non-consumptive uses was evaluated. The rule of summation was used to calculate consumptive water requirements and the rule of compatibility (i.e., maximum principle) was adapted to estimate the non-consumptive ones. It was determined that the minimum, medium and high levels of annual environmental flows are 134.22 x 10(8), 162.73 x 10(8) and 274.9 x 10(8) m(3), respectively, in the Yellow River Estuary, which represent 23.7, 28.7 and 48.5% of the natural river discharge. Water requirements differ across months. The months of May through June, August and October were identified as the most critical periods for maintaining the environmental flows. The basic purpose of water entering the system is to compensate for water losses due to evaporation and to maintain an acceptable level of salinity in the estuary. Sediment transport into and through the estuary area are likely to be directly impacted by variations in river discharge. Improved efficiency in the sediment transport regime of the Yellow River could potentially reduce environmental flow requirements of the estuary, thus freeing water resources for other beneficial uses.