Quantifying streamflow sources to improve water allocation management in a catchment undergoing agricultural intensification

Abstract

Changes in streamflow contributing sources in semi-arid catchments undergoing agricultural intensification are often poorly understood. As a result, pathways to increase resilience to environmental change are not well established. Mixing model analysis using stable water isotopes and hydro-chemical tracers was applied to evaluate streamflow sources in the Kaleya Catchment, Zambia. Results showed that strong agricultural intensification signal influenced streamflow sources in time and space. In the rainy season, streamflow mainly originated from stormwater runoff from non-irrigated areas (43 ± 13%), the perennial spring (39 ± 21%) and stormwater runoff from irrigated areas (18 ± 17%). But in the dry season, the spring (65 ± 15%) and irrigation return flows (35 ± 15%) became the important upstream sources, while downstream sources were irrigation return flows (73 ± 15%) and wastewater containing vinasse (27 ± 15%), both associated with water originally transferred from the adjacent Kafue River. Given the current importance of irrigation return flows to downstream users including ecosystems, social cooperate responsibility and/or water markets must help to improve irrigation efficiency while simultaneously ensuring downstream flows are maintained.