Exploring the Potential Impact of Reforestation on the Hydrology of the Upper Tana River Catchment

Funding Agency: USAID Sustainable Agriculture and Natural Resource Management Collaborative Research and Support Program (SANREM CRSP)

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The USAID Sustainable Agriculture and Natural Resource Management Collaborative Research and Support Program (SANREM CRSP) funded a research project at Texas A&M University (TAMU) to examine the effects of reforestation policies on impacts to the environment and economy in the upper reaches of the Tana River below Mt. Kenya.

The SWAT model was used to identify environmental impacts as well as to provide inputs into the economic analysis. For this project, data was obtained from various sources and modified for input in the SWAT model. Modification of this input data allowed for a more accurate baseline simulation that was then used to evaluate various reforestation scenarios. These scenarios provided a 30 to 55% increase in forested areas in the upper reaches of the catchment; showed a reduction in sediment load in the river and thereby siltation of the reservoir; and produced a more predictable streamflow regime. More importantly, the simulations highlighted the fact that one of the three tributaries contributing flow and sediment to the reservoir was most responsible for the siltation problems. The Thiba River subsystem accounts for only 2.8% of the catchment area, but 40% of the flow and 44% of the sediment load into the reservoir comes from that same subsystem. Finally, an economic analysis of the various scenarios was completed in order to determine the impacts of the loss of agricultural land as opposed to the maintenance costs to maintain the reservoir at current sedimentation levels.

The findings of this research will help to provide a means of developing guidelines for policy implementation by the Kenyan government that will yield the best environmental result with the least negative environmental and economic impacts.

SWAT: Environmental Consequences of Reforestation on the Upper Tana River Basin Presentation