Benchmarking Fluvial Dynamics for Process‐Based River Restoration: the Upper Rhine River (1816–2014)

Multi‐temporal analysis of river‐floodplain processes is a key tool for the identification of reference conditions or benchmarks and for the evaluation of deviations or deficits as a basis for process‐based river restoration in large modified rivers. This study developed a methodology for benchmarking fluvial processes at river segment level, focusing on those interrelations between morphodynamics (aggradation, erosion, channel shift) and vegetation succession (initial, colonization, transition) that condition habitat structure. Habitat maps of the free‐flowing Upper Rhine River downstream from Iffezheim dam (France–Germany border) were intersected with a geographic information system‐based approach. Patches showing trajectories of anthropization, changeless, progression and regression allowed for the identification of natural and human‐induced processes over almost 200 years. Before channelization, the riverine system was characterized by a shifting habitat mosaic with natural heterogeneity, high degree of surface water connectivity and equilibrium between progression and regression processes. On the other hand, the following 175 years of human interventions led to severe biogeomorphologic deficits evidenced by loss of natural processes and habitat heterogeneity, hydrological disconnection between the river and its floodplain and imbalance of progression versus regression dynamics. The main driving forces of change are found in hydromorphological impacts (channelization, regulation and hydropower plant construction). Regression processes are now almost absent and have to be the objective of process‐based river restoration measures for the studied river‐floodplain system. A sustainable view on water management and river restoration should aim at a more resilient riverine system by balancing the recovery of natural processes with societal needs. Copyright © 2016 John Wiley & Sons, Ltd.     

Performance of a fishway system in a major South American dam on the Parana River (Argentina–Paraguay)

Successful design and operation of fish passage systems are important to protect fish communities from impacts of hydroelectric dams in the Río de la Plata River basin. We evaluated the performance of an elevator lift system to pass adult fish through Yacyretá dam on the Paraná River between 1995 and 1998, both for mechanical reliability and performance. The elevator lift system was mechanically inoperative 30–38% of the time during the October–December period of greatest fish migration. Target species represented 30% of total fish number in gillnet samples in the tailwater, but constituted only 10% of the total number of fish transferred. Fish collected within the system were dominated by Pimelodus clarias (>69%), although this species represented less than 10% of captures in experimental gillnets set in the tailwater. Prochilodus lineatus, a key species, represented less than 5% of transferred fish, but constituted 22.1% of tailwater samples. Estimated number of fish transferred per year ranged between 1 210 000 (1995) and 3 610 000 (1996) with biomass ranging from 631 to 1989 tons, respectively. We estimated a fish passage efficiency of 1.88% for all species and 0.62% for target species. At this efficiency, transferred species would increase the total fish yield in the reservoir by as much as 4.9 kg/ha/year, but only 0.5 kg/ha/year for target species. We conclude that fish transfer efficiency is inadequate to maintain populations of target species in the Paraná River system. We identify critical research needs to improve the passage of fish at dams. Copyright © 2002 John Wiley & Sons, Ltd.     

Assessing the impact of human activities on hydrological and sediment changes (1953–2000) in nine major catchments of the Loess Plateau,China

The Range of Variability Approach (RVA) is employed to investigate the variability and spatial patterns of hydrological and sediment changes (1953–2000) induced by intensified human activities, i.e. the implementation of water and soil conservation measures, in nine major catchments of the Loess Plateau, China. Results indicate that: (1) streamflow and sediment load regimes were greatly changed by the implementation of conservation measures; (2) similar spatial patterns of high hydrological and sediment changes resulting from the intensive implementation of conservation measures are observed in most catchments of the middle Yellow River. However, slightly different behaviours of changes exist due to the unique complexity of hydrological and sediment processes in this region and (3) the impacts of various conservation measures on hydrological and sediment processes are closely associated with the extent and types of these measures. Engineering works have a quite immediate impact on streamflow and sediment regimes. Considerable vegetation controls are recognized as additional important driving forces for high hydrological and sediment alterations among various soil conservation measures. In vegetation controls, afforestation is the major factor causing the changes of runoff and sediment processes in these nine catchments. The results of the current study will be greatly beneficial to the regional water resources management and restoration of eco‐environmental system in the middle Yellow River basin characterized by intensified soil‐conservation measures under the changing environment. Copyright © 2009 John Wiley & Sons, Ltd.     

The Sanaga discharge at the Edea Catchment outlet (Cameroon): An example of hydrologic responses of a tropical rain‐fed river system to changes in precipitation and groundwater inputs and to flow regulation

The Sanaga River is one of Sub‐Saharan Africa's largest and greatly regulated rivers. Available flow data for this hydrosystem largely cover the pre‐ and post‐regulation periods. From comparisons between unregulated (hypothetical) and observed scenarios, it has been possible to separate and to quantify hydro‐climatic (groundwater + rainfall) change effects from anthropogenic impacts (especially dam‐related alterations). To appreciate shifts in the river regime, discontinuity detection tests and the IHA model were applied to discharge data series reflecting average and extreme flow conditions, respectively. Results obtained principally from the Hubert segmentation method reveal that a major discontinuity occurred in 1970–1971 separating a surplus phase between 1945–1946 and 1969–1970, and a deficient and much contrasted one, from 1971/1972. This implies that the Sanaga catchment is dominantly affected by hydro‐climatic changes. However, wide land cover/land use changes experienced here since 1988 have resulted in an increase in surface runoff. Additional quickflows linked to these changes may have partly compensated for the substantial decline in the dry season rainfall and groundwater inputs observed from this date. Although at the monthly scale, dam‐related impacts on average flows increase with stage of regulation, the seasonal variability of the river regime remains generally unaffected. A comparison of the IHA statistics, calculated from unregulated and observed streamflow data, show that hydrologic shifts occurring in maximum and minimum discharges are mostly significant from 1971/1972 and are mainly due to the action of dams. Minimum flows appear, however, widely impacted, thus reflecting the prime objective assigned to the existing reservoirs, constructed to supplement flows for hydroelectricity production during the dry season. Copyright © 2010 John Wiley & Sons, Ltd.