The Second IASTED African Conference on
Water Resource Management
~AfricaWRM 2008~

SCIENCE AND TECHNOLOGY INNOVATION FOR SUSTAINABLE DEVELOPMENT

September 8 – 10, 2008
Gaborone, Botswana

Runoff & Wetland Monitoring With ENVISAT ASAR Global Mode In the Okavango Basin and Delta

Wetlands in semiarid regions such as the Okavango Delta depend not only on local rainfall but also on external inflow. This can be estimated if the precipitation and other hydrological parameters of the contributing area are known. The water is intermediately stored in the soil and either evaporates, is taken up by plants or contributes to surface or subsurface runoff. While spatially continuous high resolution rainfall data are difficult to obtain, soil moisture can be derived from microwave satellite data. An approach for derivation of relative soil moisture on 1km resolution in semiarid regions has been realized within the ESA Tiger Innovator project SHARE (Soil moisture for Hydrometeorological Applications over SADC). Active microwave data which are acquired with ENVISAT ASAR operating in Global Mode have been used for the now operational processing chain. With this work we demonstrate that the relative soil moisture derived from the ENVISAT ASAR GM data can be clearly related to river discharge measurements. Additionally, we show the ability of ENVISAT ASAR Global Mode to monitor dynamics of wetland areas as a response to precipitation and soil moisture variation respectively in the upper Okavango basin.

Simulating Climate Change and Water Abstraction Impacts On the Hydrology and Ecology of the Okavango Delta

A distributed hydrological model is applied to study the impact of climate change and water abstractions on the hydrology of the Okavango Delta Wetlands. The relation between the present distribution of hydrological conditions and the occurrence of vegetation classes is investigated. By assuming that the distribution of vegetation will in the long term adapt to hydrological conditions, the simulated hydrological conditions under climate change and water management scenarios are translated into vegetation maps for these scenarios. Drier conditions are expected for the future and aquatic vegetation zones will be reduced in size. This change will however occur non-homogeneously over the Delta.

Operationalizing IWRM within the Okavango Delta, Botswana

An integrated management plan, the Okavango Delta Management Plan, has been formulated taking into account concerns of resources users, managers, and policy makers across sectors. The strategic goals of this policy are in line with integrated water resources management principles. It is therefore argued that this plan provides a framework for operationalising IWRM within the delta. The formulation of an IWRM plan for the delta is recommended.

Habitat Heterogeneity, the Flood Pulse and Dynamic Processes In a Subtropical Floodplain Fishery; the Case of the Okavango Delta, Botswana (A Review)

This paper integrates biological and social dimensions of the Okavango Delta fishery by reviewing all available literature. The main aim of this review is to produce an integrated paper that will inform policy towards a comprehensive management of the Deltas fishery. Based on the review, it is evident that the flood pulse contributes towards fish production and productivity in the Delta. Some research in the Delta shows that, typical with other floodplain systems globally, the terrestrial ecosystem is actively subsidizing the aquatic system whereby this energy is eventually channelled into fish biomass. This fish biomass is then exploited by different fisher groups in the Delta using a variety of fishing gears. Subsequently, similar to other floodplain fisheries elsewhere, fish is a major livelihood activity in the Delta. Management of fisheries resources globally has been based on classical fisheries management approaches. However, the efficacy of these is questionable due to collapses of some world fish stocks. It is on this basis that this paper advocates for a paradigm shift in fisheries management. That a new management paradigm needs to be formulated that is holistic in nature, with heavier emphasis on empiricism and less reliance on statistical or mathematical modelling.

Application of Airborne Geophysics In Large Scale Integrated Hydrological Modelling. Case Study: Okavango Delta, Botswana

Airborne geophysics is a remote sensing technique that can be used to derive some parameters that are direct inputs into distributed groundwater models, e.g., aquifer thickness. It can also be used indirectly in calculation of some parameters through model calibration, e.g., hydraulic conductivity of flow barriers knowing their locations accurately from geophysics.

This paper focuses on the integrated use of remotely sensed airborne magnetic and ground based gravity data sets in order to determine the aquifer geometry (thickness and structural trends). We further look into another geophysics technique; seismotectonics to evaluate the earth's subsidence below the delta caused by the current extensional forces.

The results show that the aquifer thickness is structurally controlled and is on average 180m thick. We estimate the earths crust to be 26km thick below the delta using gravity data. Using this information together with the calculated earthquake moments from seismic event data (1952 to 2005), we estimate an earth subsidence rate of 0.07 mm/yr.

We show thorough the use of a coupled surfacegroundwater hydrological model that earthquake movements could have played a role in influencing the surface flow regime shift observed in the Okavango Delta. This is done by tilting the most tectonically active north eastern block and the panhandle by a modest figure of 30cm in a southwest direction and simulating the effect of this on the spatial distribution of flooding frequency. An average increase of about 20% in flooding frequency is observed on the south western branch of the delta.

Change and Variability of Flooding in the Okavango Delta, Botswana, and Their Consequences to Water Resources Management

Okavango Delta is an ever-changing dynamic system. A series of factors have been identified that have the potential to affect future flooding conditions in the Okavango Delta. These include long and short term climate variability, geomorphological processes leading to shifts in flood distribution, as well as greenhouse gas-driven climate change. The changes are inevitable, although their timing and magnitude are uncertain. The current approach for management of the system does not adequately account for possible future changes and their uncertainty.