Since the construction of the Xiaolangdi reservoir in 1999, the WSM has become the most dominant signal for the Huanghe. Here, we focus on the special role of the WSM in regulating the delivery of Huanghe material to the sea.

The natural boundary between flood and non-flood seasons has been altered by the Xiaolangdi dam (Yang et al., 2008), although the monsoon still brings a majority of annual basin precipitation in the flood season. Instead, the annual WSM has become a human-made “high-water period” for the lower Huanghe. The WSM, despite its short duration, plays a vital role in delivering Huanghe water and sediment to the sea. The durations of WSM in 2002–2011 averaged ∼20 days every year, yet provided 27.6% and 48.9% of the annual Proteasome inhibitor water and sediment delivery to the sea, respectively. Notably, the WSM releases only 27.6% of the annual

water discharge, yet the released water can carry 48.9% of the annual sediment flux to the sea. Moreover, the average suspended sediment concentration of Huanghe water during WSM was as high as 17.3 kg/m3, much higher than an average of 6.9 kg/m3 in other times of the year. The WSM has therefore become a dominant regime controlling the suspended sediment concentration, grain size, water and sediment fluxes to the sea. Selleck CHIR99021 Although WSM has been regularly performed over the past decade, its regime was often modified, given its both positive and negative impacts on infilling of sediment in the Xiaolangdi reservoir, riverbed morphology, geological processes at the river mouth, and biological responses of the coastal environment. The timing and duration of these WSM-controlled “high flows” are irregular (Table 5). In 2005, for instance, WSM lasted 15 days

and produced only 0.61 × 108 t sediment (31.9% of the PLEKHB2 annual flux) delivered to the sea. In 2010, WSM was performed three times with a total duration of 38 days, resulting in the transport of up to 1.45 × 108 t sediment and 90.7 × 108 m3 water to the sea, which accounted for 86.8% and 47% of the annual flux to the sea, respectively. It is clear that the WSM regime is a major control on the annual water and sediment fluxes to the sea. Another uncertainty lies in the scouring of river-bed in the lower Huanghe, a complex process involving river flow, bed features, and human-interventions. Riverbed scouring provided an important source for the sediment flux to the sea, but relied heavily on the released floodwater from the Xiaolangdi dam. Sediment transport varies more than linearly with flow (Naik and Jay, 2011). This is also true for the Huanghe when WSM was performed. In 2004, the Xiaolangdi dam released 44.6 × 108 m3 of water during WSM, and 0.665 × 108 t of sediments were scoured. In 2009, however, the released 50 × 108 m3 of freshwater only scoured 0.343 × 108 t of sediment. During 2002–2004, water discharge released from the Xiaolangdi dam was controlled <3000 m3/s.