3. Steam corridors in watershed management
Publication of DESFIL; prepared for USAID under contract number 527-0000-C-00-7841-00; Development Strategies for Fragile Lands, 7250 Woodmont Avenue, Suite 200, Bethesda, Maryland 20814; 1989, 15 p.
Increasing human pressure on the land has accelerated soil erosion, reduced production and income levels, and created scarcities of wood and loss of natural systems. In practice, watershed management has focused on reforestation of degraded areas, on-farm soil conservation, and "works of art".
Interventions are rarely based on an integrated management plan addressing whether or where they are needed, if they are cost effective, or how they fit into an integrated management plan. Failure to distinguish in the field between relatively uncontrollable natural erosion processes and those that are accelerated by human activities can be costly and threatens the credibility of management approaches.
This paper specifically addresses the management of stream corridors.
Sediments from uplands, together with materials excavated by streams themselves, move through a network of stream corridors. How these corridors are managed is critical to the achievement of both local and downstream benefits from overall watershed management activities.
Stream corridors form the transitional zone of significant interaction between a terrestrial and an aquatic ecosystem.
Stream corridor management includes the maintenance of riparian and instream vegetation and maintenance of overall channel morphology with its obstructions, rapids, meanders and adjacent wetlands. These actions together result in:
- Filtering of sediments contained in overland runoff;
Stream corridor management is most effective in delivering these benefits if integrated into an overall program of watershed management.
Effective management of headwater streams offers higher benefits per stream segment affected. If headwater stream corridors are neglected, management of river segments in the lower reaches of a watershed will be less effective.
Financial resources are never sufficient to permit all possible management interventions in watersheds thousands of hectares in extent.
Scarce resources must be allocated to those activities which together contribute most to overall system maintenance, the well-being of local populations, and to downstream water resource users. Stream corridor management, particularly along smaller streams in both upper watersheds and lowlands, can be a cost-effective contribution to a watershed management program.
An integrated two-step ecological engineering approach to stream corridor management is recommended. First is the establishment or preservation of the filtering capacity of the corridor vegetation that serves as the buffer between the stream itself and the rest of the watershed. Second is the maintenance of the biological and physical integrity of the stream ecosystem itself. This involves protecting the stream from such direct impacts as channelization, waste dumping, and livestock watering. If both steps are effective in maintaining the integrity of the corridor with its riparian and aquatic components, then the maximum range of goods and services of local or downstream value (fisheries and wildlife, recreation, water for domestic, agricultural and industrial use, and waste removal and treatment) can be provided.
Smaller streams, because they compose a major proportion of the length of channels in a watershed, serve as the major area of interface between stream corridors and the surrounding watersheds.
The purpose of this paper was to demonstrate how stream corridor management plays an integral role in the management of watersheds for sustainable development. Stream corridors are among the most fragile elements of upper watersheds, both in mountainous areas and in the upper reaches of streams in the wet tropical lowlands. In addition to the multiple values represented by stream corridors, these areas are a magnet to conflicting uses. How human needs for food can be met while maintaining other values both on site and downstream has been our concern. Among the use strategies advocated for fragile lands has been the modification of existing small farm production activities by introducing tree-based agroforestry and silvopastoral systems to produce food and raw materials from combinations of annual and perennial cropping and livestock. These uses are complementary to, and may even be included among, the uses advocated for stream corridors.
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Review, Mexico, India, Iran, Pakistan, Australia, water harvesting systems, case examples, catchment areas, water storage, water harvesting constraints, water harvesting strategies, water quality, sources of water, precipitation, knowledge gaps, FAO
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