Abstract

Temporary freshwater pools or pans are known for their nature value and socio-economic importance especially in arid and semi-arid regions, but it is still poorly known how they develop in a natural setting. The ecologically valuable temporary freshwater pans of the Save Valley Conservancy in Zimbabwe, are studied in order to gain insights into their formation. Field observations of 17 existing pans and in situ measurements at one possible site of pan formation were done. It was observed that in most cases trees were bordering existing pans with Diospyros mespiliformis being present at eight locations and Colophospermum mopane at five. These two species were co-existing at two locations which had also dead trees present. On the basis of these observations, a suspected developing pan was followed up using hydrological field observations to understand processes that are important in pan formation. In situ infiltration tests as well as penetrometer tests, before and after a rainfall event, were completed on a grid covering 25 m2. The measurements were taken at one-metre interval and the data were krigged in order to visualise the contours. Initial insights point towards the areas in the immediate vicinity of trees acting as preferential pathways for infiltration, which is in contrast to what is needed for ponding. Based on these findings, we propose a possible theory for the formation of pans in the study area and suggest techniques for monitoring pan formation.