Where are you: Home Publications Working Papers

Development of a Groundwater Model of the Romwe Micro-Catchment, Zimbabwe: 
By Patrick Barre Moriarty
Price:  [Z$60]

This paper describes the development and use of a groundwater model of the
Romwe micro-catchment in southern Zimbabwe.  The model supports our
conceptual picture of how the groundwater system works in the freely draining
soils of the ‘red soil’ areas of the catchment.  The model shows that groundwater
recharge is indeed high, but largely lost to recession due to abstraction by deep
rooted vegetation.  This is an important finding as it has profound implications for
the management of groundwater resources.  The importance of ‘sump points’ is
illustrated by the model.  These are lower down in the catchment, where
groundwater collects and pools.  One contains the present collector will in addition
to some of the most productive private wells.  In all the simulations, groundwater
abstraction by humans was insignificant when compared to that by
vegetation/evaporation.  

The concept of well failure due to low transmissivity rather than to lack of water,
and despite an otherwise high ‘regional’ water table, is important in understanding
the mechanisms of crystalline basement acquifer behaviour.  The model gave
strong support to the development of further productive water points in the
catchment.  Given that the current collector well is designed to irrigate halve a
hectare it is suggested that up to a further 5 ha could be irrigated in the zones of groundwater accumulation using either collector wells or larger diameter wells. 
The model suggests that the ‘Romwe acquifer’ is largely isolated from the larger
catchment downstream.  At a river-basin scale it suggests that the contribution of groundwater recharge to river base flows will be negligible for all but those
micro-catchments closest to the rivers.  It also suggests that, apart from at the
micro-catchment scale, there will be negligible effects from change in landuse on
groundwater resources further downstream.  At a river-basin scale it suggests
that the contribution of groundwater recharge to river base flows will be negligible
for all but those micro-catchments closest to the rivers.  It also suggests that,
apart from at the micro-catchment scale, there will be negligible effects from
change in land use on groundwater resources further downstream.  Even within
the micro-catchment there is no guarantee  that managing one section will have
an effect on the groundwater of another.  Each catchment needs to be examined
and treated for its own unique range of soils, geology and topography.  Given
the effort in time and resources put into developing the groundwater model of
the Romwe acquifer, it is difficult to see how the approach of using a distributed
groundware model would be of much use in terms of general ‘scaling-up’.

The complexity of the basement means that entirely local effects control a highly
localized acquifer.  TO talk about groundwater as a shared resource at a
river-basin scale in such a framework is meaningless.  It is a wholly local resource,
common only to those people living in the immediate area, or microcatchment. 
In a way, this lends it to a highly localized common property resource
management approach – decisions on runoff control measures, forestry or
irrigation will have a wholly local effect and as such should be easily understood
and made relevant to local communities’ livelihoods

Back To Top