Floodplain Connectivity

What is it about?

Floodplains fulfil vital ecosystem services (supporting water management, biodiversity, agricultural production, ecotourism and others). Since a satisfactory water supply is indispensable for the provision of such services, in addition to longitudinal channel connectivity, lateral channel/floodplain hydrological connectivity is of primary importance. As a consequence of river regulation, however, floodplains shrunk considerably in area, ‘protected’ floodplains connection with the river channel which had produced them and became severely threatened ecosystems. In the Drava Plain, too, disconnected (or ‘geographically isolated’) oxbows became typical. With reduced surface connectivity, groundwater flow becomes the main driver of connecting processes (profundal type of oxbow). Effective porosity and hydraulic conductivity of alluvial deposits and seepage from an oxbow lake (the degree of clogging of floor deposits) were calculated to estimate groundwater movements and to reveal water exchange between oxbow lakes and the active river channel. Subsurface connectivity under drought conditions was simulated by hydrological modelling with the help of HYDRUS-1D and MODFLOW6 packages. Planning rehabilitation efforts subsurface connectivity too should be considere

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Photo by Alex Stuart on Unsplash

Photo by Alex Stuart on Unsplash

Why is it important?

Surface connectivity of the protected floodplain with the main channel of the Drava is very difficult to provide. Groundwater flow, however, ensures some degree of subsurface hydrological connectivity. This has to be assessed in close association with the water retention capacities of soils and alluvial deposits. Our research shows that the critical factor in water retention is the transmissivity of lakebed and adjacent deposits. It is not only the present lakeshore that has to be examined hydrodynamically but also the future shallow lakebed zone inundated after water replenishment. Based on the laboratory hydraulic analyses of the undisturbed sediment samples, highly different conductivity values were found for the middle and offshore parts of the oxbow lakes—a pattern just the opposite expected for active river channels. Relatively, coarse fraction (*80 μm) dominates the shoreline zone and allows higher seepage rate from the oxbow lake. Considerable losses to groundwater (and indirectly to the Drava River) are expected and may jeopardize the success of the replenishment scheme. Allowing for the hydraulic variability of the sediment sequence, HYDRUS-1D and MODFLOW 6 simulations showed to what extent the planned replenishment scenarios will raisethe groundwater level and allowed the estimation of soil water retention capacity

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