The contribution of rainwater harvesting from roof catchments in increasing water resources for Nairobi City County residents
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Date
2017-03
Authors
Ombuna, Christine
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
Nairobi City County is faced with acute water scarcity. The daily deficit is
currently 170,000 m3/day which accounts for about 23%. This deficit will escalate
as population increases. However, streets are often flooded during heavy rains and
water harvesting has been neglected. The County relies mainly on surface water
sources from Athi River basin, Tana River basin and over 3000 boreholes. The
objectives of this study were to assess volumes of rainwater that can be harvested
from roof catchments, sizes of storage capacity required, water quality and
adoption of rainwater harvesting from roof catchments. Five rainfall Thiessen
polygons that covered the entire County were created using ArcGIS version 9.2.
Samples of 10 maisonettes and multi-story buildings were obtained from each
Polygon. More samples of 25 industries and 25 institutions were collected making
a total of 150 samples. Data used included rainfall depths, roof surface area, size
of tanks, physical, bacteriological and chemical properties of rainwater from roof
catchments. Microsoft Excel, SPSS, descriptive analysis, regression and
correlation analysis were appropriately used in the study. The result indicated that
Kabete receives highest annual rainfall followed by Dagoretti, Eastleigh Moi
Airbase, Wilson and J.K.I.A. Over 90% of buildings would have rainwater
supplements of above 23% thus filling the current deficit. The size of storage tanks
for maisonettes ranged from 5, 126 to 60, 840 litres while multi story buildings it
ranged from 32, 400 to 344, 250 litres. A regression model for storage capacities
and their cost were generated. The quality of rainwater from different roofing
materials was not suitable for potable purposes but, it would be used for nonpotable
purposes. Majority (93%) of residents depended on city council piped
water, private boreholes (7%) and only 16% harvested rainwater as supplement to
City council or private borehole sources. Institutions are leading in roof catchment
rainwater harvesting (44%), followed by maisonettes( 20%), Multi-story buildings
6% and industries have least adopted rainwater harvesting(4%). The result
indicates that if roof top rainwater catchment is done, water deficit that has been
estimated in Nairobi County will be definitely offset. Industries and institutions
will benefit more from roof catchment rainwater harvesting followed by
maisonettes and multi-story residential buildings. Residents should be encouraged
to adopt roof catchment rainwater harvesting by enforcing policies and by laws for
roof catchment rainwater harvesting in Nairobi City County.
Description
A thesis submitted in partial fulfillment of the requirements for the award of the Degree of Master of Science in Land and Water Management, Kenyatta University. March 2017