Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China

Abstract

• Hydrological regime in the reservoir fluctuation zone has been significantly altered.• Grain-size variations are diagnostic for sedimentary stratigraphy differentiation.• Post-dam sedimentation processes were reproduced by chronology determination.• Regular flow regulation controls contemporary seasonal sedimentary dynamics. Since the launch of the Three Gorges Dam on the Yangtze River, a distinctive reservoir fluctuation zone has been created and significantly modified by regular dam operations. Sediment redistribution within this artificial landscape differs substantially from that in natural fluvial riparian zones, due to a specific hydrological regime comprising steps of water impoundment with increasing magnitudes and seasonal water level fluctuation holding a range of sediment fluxes. This study reinterpreted post-dam sedimentary dynamics in the reservoir fluctuation zone by stratigraphy determination of a 345-cm long sediment core, and related it to impact of the hydrological regime. Seasonality in absolute grain-size composition of suspended sediment was applied as a methodological basis for stratigraphic differentiation. Sedimentary laminations with relatively higher proportions of sandy fractions were ascribed to sedimentation during the dry season when proximal subsurface bank erosion dominates source contributions, while stratigraphy with a lower proportion of sandy fractions is possibly contributed by sedimentation during the wet season when distal upstream surface erosion prevails. Chronology determination revealed non-linear and high annual sedimentation rates ranging from 21.7 to 152.1 cm/yr. Although channel geomorphology may primarily determine the spatial extent of sedimentation, seasonal sedimentary dynamics was predominantly governed by the frequency, magnitude, and duration of flooding. Summer inundation by G R A P H I C A L A B S T R A C T a b s t r a c t a r t i c l e i n f o Contents lists available at ScienceDirectScience of the Total Environment j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v natural floods with enhanced sediment loads produced from upstream basins induced higher sedimentation rates than water impoundment during the dry season when distal sediment supply was limited. We thus conclude that flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone, though little impact on total sediment retention rate was detected. Ongoing reductions in flow and sediment supply under human disturbance may have profound implications in affecting sedimentary equilibrium in the reservoir fluctuation zone. The results herein provide insights of how big dams have disrupted the sediment conveyance processes of large scale fluvial systems.

Model-Based Evaluation of Hydroelectric Dam’s Impact on the Seasonal Variabilities of POC in Coastal Ocean: A Case Study of Three Gorges Project

“…The strong vertical mixing induced by the northeast monsoon increases the suspended matter concentration and thus influences photosynthesis and causes the plankton POC production capacity to decrease. On the other hand, because of the large river discharge and abundant nutrient import [26,98], especially in the summer, the CDW occupies almost the whole surface ocean at 30 • N in the ECS. Hence, under appropriate light and nutrient conditions, the CDW-influenced area and induced oceanic POC production are relatively high compared with the dry season.…”

Effectiveness of artificial floods for benthic community recovery after sediment flushing from a dam

“…Downstream sections are usually sediment starved causing substrate armoring and increased bank erosion and riverbed incision (Kondolf 1997;Graf 2006), with many detrimental ecological effects. By contrast, in the upstream impounded reach, sediment trapping in reservoirs dramatically alters the morphological and ecological features of the systems, decreasing substrate particle size and transforming the river into a lentic body (Tang et al 2016;Rothenberger et al 2017). Moreover, sediment accumulation within impoundments reduces storage capacity of reservoirs, interfering with the functional purpose of the dam and reducing the efficiency of associated hydroelectric power plants (Annandale 2013).…”

The Spatiotemporal Variability of Evapotranspiration and Its Response to Climate Change and Land Use/Land Cover Change in the Three Gorges Reservoir

“…The Three Gorges Project was started in 1994 and began impoundment in June 2003. The water table of the reservoir reached 135 m in June 2003, 156 m in October 2006, and 175 m in October 2010 [6]. The Three Gorges Project has brought economic and social benefits to the region such as flood control, power generation and shipping, and the Three Gorges Reservoir (TGR) is a unique region formed after the Three Gorges Project was carried out in China.…”