The influence of land use patterns on runoff and soil erosion in the River Nyando Basin at Kobong'o area in Kenya

Abstract

Riparian areas though small, are widely recognized as crucial to the overall ecological health of the watershed. Many of them are however, in degraded conditions largely as a result of poorly managed agricultural and grazing activities. Over half of the world's riparian zones have been destroyed by human activities because of their proximity to the flood plains, and therefore suitability for agriculture. This study, using the historical land use patterns set out to investigate the possible causes and magnitude of soil erosion along the River Nyando basin at Kobong'o area. It also examines the local community perception of the identified land use changes and degradation problems in the area. Land degradation in the watershed is of concern in terms of the ecological stability and socio-economic well being. Soil erosion is evident in most parts of Nyando District and has recently been rated by farmers as the most urgent problem. The specific objectives are: to determine historical land use changes and river dynamics in the study area; to compare runoff, sediment and nutrient (N & P) loss from different land use types; and to assess the local community perception on riverine ecosystem management.

Buffer strips and conservation crops can empirically provide for net costs to farmers as well as protect the fragile riverine areas from degradation. They control soil erosion, nutrient and water loss and provide additional services and products to the community. Most conservation technologies are underutilized due to a variety of reasons such as lack of demonstrable profitability at the farm level. It therefore requires a combination of both biophysical and socio-economic considerations to design any management strategy for riverine areas. The perception of the local community is paramount as is their involvement in the design process from the initial stages. The "Retirement Theory" developed in New Zealand promoted exclusion of any exploitation activity along the waterways, which are then planted with natural vegetations due to their protective potentials. The theory did not attract the farmers' socio-economic priorities.

Historical land use patterns are examined by use of selected digitized aerial photographs from 1948. Soil, nutrient and water loss is captured in terms of different land use types using 100m2 plots through pipe samplers and laboratory analysis. A participatory Rural Appraisal is conducted to collate the views, needs and understanding of the community as concerns riparian resources.

The results indicate over cultivation particularly on fragile lands, high soil and water losses from cattle tracks, and lack of awareness on the importance of long-term management strategies. It can be argued that increased soil conservation and fertility management and improvement activities are required in this area. There is also need to restrict cattle movement on fragile landscapes. Participatory awareness creation on the value of sustainable management strategies for the riparian zones and need for communal protection of shared resources are the other intervention points that needs to be looked into. Further research should be conducted and indigenous and exotic tree and shrub species that provide both resource protection and socio-economic return to farmers be developed. Acceptable means of confining cattle such as Zero grazing could be looked into.