Abstract
Dam operation has been widely deployed to mitigate the risks of ice jam flooding, but it may result in a decrease in the discharging capacities of downstream river channels. The Ningxia-Inner Mongolia reach of the Huanghe River (Yellow River) has historically suffered numerous disasters caused by ice jam flooding, and three large dams have been jointly operated to mitigate such risks since 1968. Whilst the resultant significant increases in both the annual runoff and mean water temperature during the ice jam flooding seasons helped to shorten the freezing-up duration and reduce the thickness of the ice cover, a significant channel shrinkage occurred in the reach when the dam operation took place under the input of a relatively larger amount of sediment from the upstream. In the new flow regime that commenced in 2008, a detailed examination of the river channel-form adjustments and the resultant changes to the discharging capacities identified a slight increase in the discharging capacity of the channel along the entire study reach. This was mainly due to a significantly smaller amount of sediment load being carried by a slightly increased annual runoff. Whilst it was demonstrated that the dam operation was still an effective means for mitigating the risk of ice jam flooding in the Ningxia-Inner Mongolia reach under the new flow regime, care needs to be taken when the favorable flow-sediment condition changes. Furthermore, the effectiveness of the dam operation appeared to vary significantly at the channel sections of different planforms; thus, more detailed studies are required.
Highlights
Ice jam flooding normally occurs in rivers that encounter ice jams or a wide range of downstream ice cover [1,2]
The Ningxia-Inner Mongolia reach of the Upper Yellow River in China is an area that has historically suffered numerous disasters caused by floods, from ice jam flooding [29]
Knowledge is required on how the joint dam operation helps in mitigating the risks of ice jam flooding in the Ningxia-Inner Mongolia reach of the Upper Yellow River under the new flow regime
Summary
Ice jam flooding normally occurs in rivers that encounter ice jams or a wide range of downstream ice cover [1,2]. Long-term temperatures below 0 ◦ C and a change in the river flow direction from a low latitude to a high latitude are the two main factors causing the occurrence of ice jam flooding [3,4,5]. During the freezing-up and breaking-up periods of river flow, disasters to local communities from ice jam flooding are prone to appear [6,7,8]. Significant mitigation of the risks from ice jam flooding can be achieved by the construction and operation of dams to alter the hydrological process and thermal conditions of river flow [12,13,14]. Many large rivers in cold regions, such as the Yellow River (Huanghe River), Vistula River, all Siberian Rivers, and so on, frequently experience ice jam flooding because these rivers are located in high latitude areas and they flow northward in many reaches [9,10,11].
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