496
A. Vushe
According to CSE (2002a), watershed management is an effective method to intercept dispersed runoff. Many techniques for water conservation have been developed
along hill slopes with the intention to prevent soil erosion and reduce surface runoff,
and then increase infiltration in the ground to recharge aquifers. This could increase
recharge of aquifers as well as water retention, which, on a large scale, can change
hydrological conditions within a river basin for a considerable period of time. Before
such an approach could be attempted, thorough analysis of the impacts of catchment
modification using soil and water conservation measures on the hydrology of each
catchment would be required. In extremely arid catchments, several techniques have
been tested to improve control and regulation of flash floods (spate) and reduce
sediment transport. Unfortunately, current design and feasibility studies are often
hampered by lack of adequate data on runoff from flash floods (Hatibu and Mahoo
2000). Therefore, data collection and more researches are required to devise better
methods to harvest, treat water, and recharge aquifers for entire river catchments in
a cost-effective way when there are flash floods. Other techniques that may also be
tested are use of check dams, underground dams, and sand dams, as well as use of
various types of artificial recharge wells.
Peak runoff is a significant proportion of the total discharge of rivers, and it usually
occurs during periods with the smallest water demand (FAO 1995). Transferring
water from the high-supply season to the high-demand season is a challenge usually
solved by storing surface water behind dams. Unlike storage of water in aquifers,
surface reservoirs have evaporation and sedimentation problems, for which practical
and sustainable solutions must be developed. Groundwater storage is seldom harmful
to the environment, but groundwater aquifers rarely have large storage capacity, so
they generally cannot absorb great volumes from floods in a short period of time,
and they also have low water yields per well (CSE 2002a). Therefore, water experts
must find a balanced, practical conjunctive water storage systems for surface and
groundwater, especially for water-stressed dry areas where optimizing catchment
water retention is a priority. A practical example is the Omaruru Delta Reservoir
and aquifer artificial recharge system, in the Namib Desert, that supplies water to
Namibian coastal towns. A surface storage reservoir is used to harvest flood water
and clarify the water by natural settlement of suspension for a few days. The clarified
water is used to recharge an aquifer, which is a cost-effective solution for retention
of water in the catchment.
Aquifers can offer natural water distribution systems to water users within
and between neighboring catchments. This requires extensive knowledge of the
hydrology of the catchments and of the nearest aquifers including the energy and cost
implications, inter-basin transfers, and linkages. Aquifers may leak into other catchments, and hence they are natural conduits of water for inter-basin water transfer.
Understanding the hydrogeology of all transboundary catchments and aquifers
requires careful hydrogeological investigation to avoid conflict if equitable water
allocation and abstraction are to be implemented under these conditions. One typical
example is the Nubian Sandstone Aquifer in the Sahara Desert that lies beneath Egypt,
Libya, Sudan, and Chad, believed to be the largest fossil aquifer ever discovered. Total
and useful volumes vary greatly. Some studies suggest that the groundwater there
A. Vushe
According to CSE (2002a), watershed management is an effective method to intercept dispersed runoff. Many techniques for water conservation have been developed
along hill slopes with the intention to prevent soil erosion and reduce surface runoff,
and then increase infiltration in the ground to recharge aquifers. This could increase
recharge of aquifers as well as water retention, which, on a large scale, can change
hydrological conditions within a river basin for a considerable period of time. Before
such an approach could be attempted, thorough analysis of the impacts of catchment
modification using soil and water conservation measures on the hydrology of each
catchment would be required. In extremely arid catchments, several techniques have
been tested to improve control and regulation of flash floods (spate) and reduce
sediment transport. Unfortunately, current design and feasibility studies are often
hampered by lack of adequate data on runoff from flash floods (Hatibu and Mahoo
2000). Therefore, data collection and more researches are required to devise better
methods to harvest, treat water, and recharge aquifers for entire river catchments in
a cost-effective way when there are flash floods. Other techniques that may also be
tested are use of check dams, underground dams, and sand dams, as well as use of
various types of artificial recharge wells.
Peak runoff is a significant proportion of the total discharge of rivers, and it usually
occurs during periods with the smallest water demand (FAO 1995). Transferring
water from the high-supply season to the high-demand season is a challenge usually
solved by storing surface water behind dams. Unlike storage of water in aquifers,
surface reservoirs have evaporation and sedimentation problems, for which practical
and sustainable solutions must be developed. Groundwater storage is seldom harmful
to the environment, but groundwater aquifers rarely have large storage capacity, so
they generally cannot absorb great volumes from floods in a short period of time,
and they also have low water yields per well (CSE 2002a). Therefore, water experts
must find a balanced, practical conjunctive water storage systems for surface and
groundwater, especially for water-stressed dry areas where optimizing catchment
water retention is a priority. A practical example is the Omaruru Delta Reservoir
and aquifer artificial recharge system, in the Namib Desert, that supplies water to
Namibian coastal towns. A surface storage reservoir is used to harvest flood water
and clarify the water by natural settlement of suspension for a few days. The clarified
water is used to recharge an aquifer, which is a cost-effective solution for retention
of water in the catchment.
Aquifers can offer natural water distribution systems to water users within
and between neighboring catchments. This requires extensive knowledge of the
hydrology of the catchments and of the nearest aquifers including the energy and cost
implications, inter-basin transfers, and linkages. Aquifers may leak into other catchments, and hence they are natural conduits of water for inter-basin water transfer.
Understanding the hydrogeology of all transboundary catchments and aquifers
requires careful hydrogeological investigation to avoid conflict if equitable water
allocation and abstraction are to be implemented under these conditions. One typical
example is the Nubian Sandstone Aquifer in the Sahara Desert that lies beneath Egypt,
Libya, Sudan, and Chad, believed to be the largest fossil aquifer ever discovered. Total
and useful volumes vary greatly. Some studies suggest that the groundwater there