The Impact of Flooding Characteristics on Cotton Cultivation in Lower Kano Plain in Nyando District, Western Kenya
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Date
2010
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Abstract
Flooding continues to be a common environmental hazard in both developed and
developing countries. Kenya has not been spared by the destruction that is usually
associated with floods. Crops, settlement and infrastructure are usually impaired
wherever flooding occur. The severity of damage as a result of floods has been
documented to have had a relationship with the flood magnitude, flood frequency and
occupation of the flood prone floodplains of large rivers. In the Lower Kano Plains of
Western Kenya, damage to crops by floods is exacerbated by occupation of the lower
reaches of the Nyando River.
This study sets out to assess the impact of flooding characteristics of the Nyando
River on cotton cultivation in the Lower Kano Plains. In particular, the study
examined the characteristics of the Nyando River Basin with the aim of describing
how the river morphometry could have influenced flooding in the Lower Kano Plains.
Also investigated, is the change in the flood magnitude and frequency with time and
space, and finally, what anecdotal data (perception of cotton farmers) are available to
support the assessment of flooding on cotton cultivation.
The study deployed both quantitative and qualitative research methods in examining
the variability of rainfall and flow and the consequent impacts of flooding on cotton
cultivation. Households living downstream in Lower Kano Plains were the target
social unit of analysis. Multi-stage sampling technique was used to sample the
respondents whom were interviewed through the use of a self administered
questionnaire schedule. Descriptive and inferential statistical techniques were used in
data analysis. Relevant probability models were used to analyze the flood magnitude and flood frequency. Generally, the findings related to the research question have
shown that flooding in the Lower Kano Plains has inhibited cotton cultivation and
lower crop acreage. Furthermore, output has significantly declined for the period
when spate has either denied farmers the ability for early planting or destroyed cotton
already in the fields.
The inter-seasonal and intra-seasonal variability of rainfall and flow show their first
peaks are dominant in April and May, while October and November present the
second cycle. There is however, a shift in the cycles towards August and September,
making the annual flow cycle highly variable in terms of decisions for crop growing.
These peaks interfere with the cotton growing calendar, and results in delays in
planting or destruction of cotton already planted.
The results from the spectral analysis revealed a strong annual and biannual cycle of
both rainfall and flow, and an oscillating 4 months cycle that exhibited climate
instability. A strong seasonal signal was evidenced between 6 and 12 month period
that correspond with the flooding peaks. Similarly, wavelet results demonstrated a
strong 12 month spectrum of both rainfall and floods with a large frequency of
oscillation in the later period of the 31-year time series. The high power band of 2 to 5
years for both the raw and filtered rainfall and flow time series revealed a Quasi
Biennial Oscillation (QBO) and a shift in the rainfall and flow cycle. The findings of
the correlation also revealed that (r2
= 0.278) rainfall in catchment explains 27.8% of
high flow. The rest (72.2%) is attributed to other factors such as anthropogenic or
hydro geologic characteristics of the study area. The study area was revealed to be
prone to between 3 and 7 years flood return frequency with an average magnitude of
400 m3/sec. Further results showed that out of the 31 years of continuous time series flow the Nyando River recorded 18 years of bankful flow (200 to 387.6 m3/sec). The
high frequency of bankful flow illustrates that Nyando River has limited channel
capacity and is therefore vulnerable to flooding downstream.
The 1 year return frequency characterizes the Lower Kano Plains to crop damage by
annual spates, and thus, demands a shift in the cropping pattern and or change of crop
variety to those ones that withstand poor drainage. Other factors that have exacerbated
the decline in cotton production include poor price of lint, competition from synthetic
fibres and rising cost of cotton production. Because of poor remuneration from cotton
production, farmers are shifting to the growing of other crops such as rice and
sugarcane that are less affected by flooding conditions. The two latter crops are said
to be highly viable, cost effective and reliable. The problem of cotton cultivation in
the study area is therefore due to variability of hydrologic conditions and economic
factors. There is a need for a sound flood mitigation policy as well as the adoption of
appropriate agronomic practices that would enhance cotton cultivation and improve
output in the flood prone areas for it to be profitable in the present economic climate.
Description
DISSERTATION SUBMITTED TO THE FACULTY OF SCIENCE AND AGRICULTURE
FOR THE DEGREE OF MASTER OF SCIENCE IN HYDROLOGY IN THE DEPARTMENT OF HYDROLOGY AT THE UNIVERSITY OF ZULULAND, 2010.
Keywords
Flooding--Kenya, Environmental hazard, Nyando River Basin, Cotton cultivation