| dc.description.abstract | This study investigated the characteristics of rainfall and quantified the probable volume of
water that can be harvested from rainfall inputs. The region of study considered was
Machakos district in Kenya. The area lies within (1.0oS -2.0oS) and (37.0oE-38.0DE).
Daily rainfall data from fourteen stations was used covering a period from 1960 to 2004. The
data was obtained from Kenya Meteorological Department headquarters, Dagoretti in Nairobi.
Data on water consumption was obtained by using a questionnaire in an exploratory survey of
the study area. The questionnaire also contained information on sizes of roofs of the houses in
the region.
Missing data were estimated using the linear interpolation formula. To test consistency of
precipitation data in this project, a single mass curve was used. To determine variability of
rainfall in the study area, time series analysis was used. Annual variation of rainfall was
investigated using trend analysis. To determine the area of roof catchments, an exploratory
survey was conducted in the area of study. Roof areas were determined by using a conversion
factor multiplied by ground measurements of the houses. The minimum water demand in the
area of study was investigated by obtaining the number of 20 litre jerry cans of water used
daily for domestic purposes; drinking, cooking, washing, watering domestic animals etc. An
appropriate volume of tank required to store excess harvested rainwater was estimated using
the supply method. Satisfaction levels were inv~~tigated to assess the degree to which
storages could supply enough volume of water i6 satisfy minimum demands. Reliability
indices were investigated to estimate the fraction of time when the tanks contained water.
Analysis results indicated that there was high variability of temporal distribution of rainfall
over the years in all stations. All stations had less than 60 rainy days in a year. Amount of
rainfall was higher during October-November-December seasons than March-April-May
seasons in most stations. The per capita volume of water requirement per day was computed
as 23.3 litres. In the study area, 96% of the houses were roofed with iron sheets. Harvestable
volume of rainwater was below the minimum water demand of 4.26 m3 per month in all
stations. Excess harvestable volume of water over its minimum demand was mostly
experienced in April and November. The rest of the months experienced deficits of rainfall,
with the driest months being July and August. Satisfaction of minimum demand by
harvestable rainwater varied greatly over the months, ranging from 1% in July and August to
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over 100% in April and November. Reliability indices of storages varied from month to
month, ranging from 4% to 36%. | en |
