Key factors affecting the initiation and progress of gullying in dambos in parts of Zimbabwe and Malawi

Abstract

Accelerated gullying of dambos (seasonally waterlogged bottomlands) on commercial farms in Zimbabwe has resulted in legislation curtailing dambo cultivation, even in indigenous farming areas. The transfer of indigenous cultivation to interfluve areas and the resultant concentration of cattle grazing in dambos initiated similar gullying. Facilitated overland flow was perceived to be the cause of gullying both in the case of dambo cultivation and dambo grazing, this overland flow re-excavating what was believed to be fluviatile infill.Geomorphological evidence is assembled to show that dambos are not 'fossil' fluviatile systems, nor is their clay infill alluvial. They are the 'lows' of a landsurface irregularly lowered by differential leaching. The infill forms by precipitation of materials leached from the interfluve profiles and discharged into the dambos. The fluviatile-like configuration of dambos is attributed to integration of sub-clay groundwater movement, resulting from landsurface incision. Accelerated gullying in Zimbabwe is deduced to be caused by breaching of the dambo clay by subsurface water movement. The particular vulnerability of Zimbabwe dambos is attributed to: (1) the watershed situation; (2) shallow weathering and (3) the thinness of the dambo clay. Evidence from Malawi indicates that interfluve deforestation and cultivation of shallow-rooted crops conserve water, raising the groundwater level. Such an increased head of groundwater also appears to have occurred in Zimbabwe; this would strengthen upward discharge in the dambos, promoting gullying. Urgent land and water policy revision is required, allowing restoration of dambo cultivation and reafforestation of interfluves, if dambos are to be conserved and the resources which they offer satisfactorily utilized.

The hydrodynamic response of a semi-arid headwater wetland to technical rehabilitation interventions

“…Similar phenomena have been experienced with wetland processes and gully erosion associations in other degraded landscapes (e.g. Whitlow, 1989;McFarlane and Whitlow, 1991;McHugh et al, 2007).…”

Creating local institutional arrangements for sustainable wetland socio-ecological systems: lessons from the ‘Striking a Balance’ project in Malawi

“…Experience elsewhere in Southern Africa has shown that dambo exploitation can lead to soil erosion, gully formation, water shortages and subsequently the loss of dambo-based livelihood opportunities (Faulkner & Lambert 1990;McFarlane & Whitlow 1990). There are also conflicts over use of these resources as people compete for access and control (Chisinga & Kayuni, 2011).…”

“…Indeed, the FLA can be seen as one of many integrated landscape approaches which have emerged in recent years as a means of conceptualising and reconciling the tensions between conservation and development at multiple scales and with multiple stakeholders (de Groot et al 2010;Sayer et al 2013;Milder et al 2014). This is exemplified in the case of dambos, where degradation in the form of soil erosion and gullying has been attributed to destructive upland catchment land use activities such as deforestation and intensive agricultural production (McFarlane & Whitlow 1990). The FLA recognises such linkages and proposes a range of physical measures to mitigate and adapt to the negative impacts; measures which include afforestation initiatives, the designation of natural vegetation buffer zones around dambos, contour terracing, and composting; all of which are key components of an integrated, holistic system of wetland management.…”

Basement and alluvial aquifers of Malawi: An overview of groundwater quality and policies

“…Besides quality studies, some cited examples include (1) investigation of the weathered basement aquifers (Jones, 1985;Acworth, 1987;Chilton and Foster, 1995), (2) major village water supply programme featuring the introduction of village level operation and maintenance of hand pumps (SmithCarington and Chilton, 1983), (3) Dambo research (McFarlane and Whitlow, 1990;McFarlane and Bowden, 1992) and (4) improving community based management of boreholes (DeGabriele, 2002).…”