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| Titel |
Storing and sharing water in sand rivers: a water balance modelling approach |
| VerfasserIn |
D. Love, P. Van der Zaag, S. Uhlenbrook |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250031213
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| Zusammenfassung |
| Sand rivers and sand dams offer an alternative to conventional surface water reservoirs for storage. The alluvial
aquifers that make up the beds of sand rivers can store water with minimal evaporation (extinction depth is 0.9 m)
and natural filtration. The alluvial aquifers of the Mzingwane Catchment are the most extensive of any tributaries
in the Limpopo Basin. The lower Mzingwane aquifer, which is currently underutilised, is recharged by managed
releases from Zhovhe Dam (capacity 133 Mm3). The volume of water released annually is only twice the size
of evaporation losses from the dam; the latter representing nearly one third of the dam’s storage capacity. The
Lower Mzingwane valley currently support commercial agro-businesses (1,750 ha irrigation) and four smallholder
irrigation schemes (400 ha with provision for a further 1,200 ha).
In order to support planning for optimising water use and storage over evaporation and to provide for more
equitable water allocation, the spreadsheet-based balance model WAFLEX was used. It is a simple and userfriendly
model, ideal for use by institutions such as the water management authorities in Zimbabwe which
are challenged by capacity shortfalls and inadequate data. In this study, WAFLEX, which is normally used for
accounting the surface water balance, is adapted to incorporate alluvial aquifers into the water balance, including
recharge, baseflow and groundwater flows.
Results of the WAFLEX modelling suggest that there is surplus water in the lower Mzingwane system, and
thus there should not be any water conflicts. Through more frequent timing of releases from the dam and
maintaining the alluvial aquifers permanently saturated, less evaporation losses will occur in the system and
the water resources can be better shared to provide more irrigation water for smallholder farmers in the highly
resource-poor communal lands along the river. Sand dams are needed to augment the aquifer storage system and
improve access to water.
An alternative to the current scenario was modelled in WAFLEX: making fuller use of the alluvial aquifers
upstream and downstream of Zhovhe Dam. These alluvial aquifers have an estimated average water storage
capacity of 0.37 Mm3 km |
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