The Water Balance of the Kimakia Catchments

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Blackie J.R
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As described in Section 3.1.1, the original objective of this study was to determine the effects on the hydrology of this area of the south-east Aberdare Mountains of a change in land use from the indigenous bamboo forest to pine plantation. The central part of the experimental programme comprised the instrumentation of two catchments and a meteorological site to measure rainfall, stream flow, and soil Moisture change and the meteorological variables necessary to estimate Penman's potential evaporation. Those parts of the 36.4 ha Catchment A conforming to the Forest Department criteria regarding slope and distance from the stream discussed in Section 3.1.2, amounting to 27.5 ha or 75 per cent of area, were cleared and planted to Pinus patula. The second catchment, designated Catchment C, was of area 64.9 Ha and remained under bamboo. Hydrological measurements were recorded on these two catchments from 1958 onwards. A preliminary Analysis of these data was presented by Pereira et al. in 1962. This showed that water use by the experimental catchment was some 40 per cent lower than the control catchment immediately after clear felling, but Increased rapidly as the pines developed. The very high infiltration rates of these forest soils of volcanic origin resulted in no appreciable increase in surface runoff from the overall 1.5 per cent of rainfall recorded in the control Catchment C during the period in which Catchment A was cleared and planted. Further analyses, presented by Dagg and Blackie in 1965, indicated that water use by the experimental catchment appeared to be stabilizing by 1964, when the pines were some 12 m tall. However, indications of a departure trend between the two catchments required further investigation.
East African Agricultural And Forestry Journal, 43 (Special Issue), p. 155-174