Monitoring the bank storage dynamics component of the riparian water balance in the Sabie River, Kruger National Park

Transpiration by riparian vegetation is a major consumptive water use in natural river systems, and must be considered when making water allocations for environmental conservation. Transpiration needs can be estimated by integrated modelling of bank storage dynamics, transpiration processes, and river hydraulics. Development and application of the bank storage model require field data describing the response of the phreatic surface to river stage fluctuations, the spatial and temporal distributions of water content in the unsaturated zone, and the geometry of the bedrock boundaries. A site on the Sabie River in the Kruger National Park, South Africa, is currently being monitored to collect such data. The phreatic surface response is interpreted to improve understanding of the nature of the subsurface flow, and its response to transpiration. Measurement of soil moisture by neutron probe and laboratory analysis has confirmed the effectiveness and reliability of the neutron probe method, and provided the necessary calibration data. Delineation of bedrock boundaries by physical probing and the use of ground-penetrating radar has demonstrated the effectiveness of the radar technique.