This study aims to assess the impact of the flood characteristics of the Nyando River on cotton cultivation in the Kano Lower Plains. In particular, the study examined the characteristics of the Nyando River Basin with the aim of describing how the morphometry of the river may have influenced flooding in the Lower Kano Plains.
INTRODUCTION AND PROBLEM SETTING
INTRODUCTION AND CONCEPTUAL FRAMEWORK
In recent years, many river systems in the world have caused several major floods (Penning-Rowsell, 1996). Halcrow and Partners (1994) also argue that deforestation and changing land use in the watersheds of Brazil's forests have increased stream flow during the rainy season.
C ONTEXTUAL S ETTING
In the Kano Plain, about 60 percent of households are temporarily denied access to farmland when it is flooded (Njogu, 2000). In the early 80s, the textile industry was the leading manufacturing activity in Kenya, both in terms of size and employment.
S TATEMENT OF THE P ROBLEM
Ikiara and Ndirangu (2003) further point out that late planting of cotton in Nyanza Province, especially in Nyando District of Kenya, exposed cotton to the onset of the long dry period. Since cotton is mostly intercropped with either corn or beans, mainly after the weed season (March), there is generally a delay in the planting of cotton.
A IM AND O BJECTIVES OF THE STUDY
R ESEARCH Q UESTIONS
O RGANISATION OF THE DISSERTATION
What anecdotal data (perceptions of cotton farmers) are there to support the assessment of flooding on cotton cultivation. Description and interpretation of anecdotal data to support the impact of flood feature assessment on cotton cultivation is presented.
O PERATIONAL D EFINITIONS
S UMMARY
BACKGROUND OF THE STUDY AREA IN NYANDO BASIN
I NTRODUCTION
L OCATION AND S IZE OF THE S TUDY A REA
T HE P HYSIOGRAPHY OF THE K ANO P LAIN AND N YANDO BASIN
The Nyando River originates in the highlands of the Nandi Hills at an altitude of over 1700m above sea level. The lower reaches of the Nyando River are characterized by pronounced meandering over a wide floodplain, the bed width is estimated to increase to approximately 50m and the gradient further flattens to 1:170 (National Environment Management Authority, 2004).
C LIMATIC CHARACTERISTICS AND A GRO - ECOLOGICAL ZONES OF K ANO P LAINS
The rainfall pattern in the Kano Plains also responds to the influence of the Intertropical Convergence Zone (ITCZ). The simulated experiment in Figure 2.7a reveals a weaker onshore wind front confined to the western edge of the lake surface (Anyah et al., 2003).
S OIL CHARACTERISTICS , FLOODING AND LAND USE IN THE K ANO P LAINS
The poor drainage of vertisols and the impact of flooding on land use in the study area are additionally shown in the lower panels. In the background, the disruption of the settlement due to the flood waters of the Nyando River can be seen.
S ETTLEMENT IN THE N YANDO BASIN AND FLOOD PRONE STUDY AREA
Although Vertisols dominate the study area and are considered suitable for cotton production, frequent flooding, waterlogged conditions and obstructed drainage continue to cause physical damage and also limit crop areas. Population density in Nyando Basin and Lower Kano Plain is shown in Figure 2.9.
T HE CULTIVATION OF COTTON AND FLOOD PROBLEMS IN THE K ANO P LAIN
The main cotton varieties grown in the Kano Plain are UKA (59) 240 and BPA 75, both medium to tall. UKA is grown under rainfed conditions found in the Kano Plain, while BPA is grown under irrigation.
S UMMARY
LITERATURE REVIEW
- INTRODUCTION
- F LOODING AND FLOOD DRIVING MECHANISMS
- D RAINAGE BASIN CHARACTERISTICS AND FLOODING
- L INKS BETWEEN LAND COVER ( LAND USE ) AND FLOW GENERATION
- T HE CAUSE OF FLOODING AND INUNDATION ON CROP CULTIVATION
- C OTTON GROWING ON THE K ANO P LAINS IN K ENYA
- S UMMARY OF LITERATURE REVIEW
For example, Bolton et al., (2007) wrote that extreme deforestation in the Himalayas, in Nepal, undoubtedly contributes to the sedimentation problems of the rivers draining the region. Zang et al., (2000) reported that deforestation in the upper Yangtze basin in China led to a decline in forest cover from 22% of the total area in 1957 to. In the past, local communities under the supervision of the chiefs of administration have carried out anti-flood works in the Kano area.
DATA AND METHODOLOGY
A PILOT A NECDOTAL S URVEY
R ESEARCH Q UESTIONS
The purpose of the research questions in this study was to help the researcher concentrate on the problem under study as well as on the purpose of the study.
R ESEARCH M ETHODS
This was complemented by a qualitative approach, where observation and recording of flood-prone areas, household locations, flood damage to crops and infrastructure, and general observation of the downstream flow of the Nyando River was carried out and described. . Some perceptions of flood characteristics that were not captured in the questionnaire interview schedule were captured through informal interviews and observations. The approach focused on daily household activities related to rainfall, flooding, river flow and crop cultivation.
P OPULATION AND S AMPLE F RAME
In this study, the sample populations are represented by the households living in the Lower Kano Plain in the lower reaches of the Nyando River. These households were treated as a representative sample of the households living in the Kano Plain. Only the households defined by the study area (Figure 4.1) inland from the Nyando River Estuary in the Lower Kano Plain were included in the study.
D ATA T YPE AND S OURCE FOR P HYSICAL (H YDROLOGIC ) A NALYSIS
Widely used in this study is rainfall data obtained from rain gauge and stream station 1GD03 located on the Ogilo Bridge downstream of the Nyando River (which is referred to here as Kano Station). The first aim of this study is to describe the characteristics of the Nyando Drainage Basin. The second goal of this study was to determine whether the flooding characteristics of the Nyando River have changed over time.
S UMMARY
It was also found that most of the rain gauge stations upstream were not operational and there was a general lack of recent records as the majority were destroyed during the 1996/1998 El-Nino related weather changes associated with the devastating floods in Kenya (Njogu, 2000; ICRAF, 2001). The majority of the cotton farmers interviewed did not keep records of their farm activities; thus, it was difficult to determine farm sizes, cotton output, use of inputs, as well as consistency in cotton production by individual households. However, this problem was solved by seeking information on output and cotton inputs sold to farmers by officials of the Lower Kano Cotton Co-operative Societies, the Area Head, and the Kisumu District Agricultural Research and Extension Officers.
ANALYSIS, INTERPRETATION AND PRESENTATION
INTRODUCTION
The variability of mean annual rainfall in the Nyando Basin is shown in Figure 5.5. The analysis uses the 31-year (1970 to 2000) rainfall and streamflow data to examine these variations. The observed trend and pattern are useful to investigate the flood characteristics of the Nyando River in the study area.
In the previous analysis of the seasonal, inter-annual and intra-annual variability of precipitation and flows has been revealed. 9 Anecdotal perceptions of the impact of flood characteristics on cotton cultivation in the Lower Kano Plains.
T HE P HYSICAL AND R AINFALL C HARACTERISTICS OF THE N YANDO B ASIN
T HE IMPACT OF RAINFALL AND FLOW REGIMEN IN THE K ANO P LAINS
The seasonal and periodic variation of rainfall and flow regime in the study area is further discussed in section 5.2.7. In this study, the use of a 31-year time series of rainfall and streamflow is sufficient to determine the trend and seasonal pattern of both rainfall and streamflow in the Kano plain. Further analyzes of the spectral density of the first and second seasons for precipitation and flow are then presented in Figure 5.14 in the following section.
The wavelet power spectra for precipitation and flow in the Kano Plain are shown in Figures 5.15a and 5.15b. The results presented in section 5.2 have broadly demonstrated the seasonal and periodic patterns of rainfall and flow in the Kano Plain.
I MPACT OF FLOODING CHARACTERISTICS ON COTTON CULTIVATION IN THE K ANO P LAINS
More than half (69) of the respondents considered the destruction of cotton bolls as the dominant problem in this regard, while almost three-quarters (70) of the respondents believed that damage to cotton seedlings was the worst. Some of the cited implications of flooding characteristics on the cotton growth cycle are presented in Table 5.21. According to Table 5.21, more than three-quarters (80%) of the respondents said that floods reduced seed germination.
S UMMARY
The long precipitation and flow peaks correspond to the cotton planting season in the study area. This is further confirmed by the wavelet results, where a quasi biennial oscillation (QBO) of precipitation and flow with a higher frequency in the later hydrological period is evident. The high wavelet spectrum in the later period is attributed to a shift in the cycles of rainfall and subsequent flow, as seen in the shaded region of the spectral band in the mid-1980s and 1990s, where flooding is strongly signaled .
INTRODUCTION
It is generally evident from the results that most farmers living in the Lower Kano Plain are highly vulnerable to the impact of the changing flow regime of the Nyando River, especially flooding and inundation. The seasonal variation of rainfall and flow has been demonstrated, and the trends of the deviations are apparently not random, as floods tend to occur between the first and second rain cycles. In addition to this, climatic and hydrological factors such as drought and flooding have been repeatedly cited as having negative effects on the cultivation of cotton in the Kano Plain.
C HARACTERISTICS OF THE DRAINAGE BASIN OF THE N YANDO R IVER
The results suggest that precipitation is the major driving mechanism and that runoff causing floods and inundations originates from the high-elevation zones with annual precipitation between 1600 and 2400 mm. According to this study, the non-harmful discharge [200m3/sec] cited by NEMA (2004) could equally contribute to the floods recorded in recent times. This is due to frequent floods and damage in the 1990s, which occur almost on an annual basis.
T HE TEMPORAL AND SPATIAL VARIABILITY OF RAINFALL AND FLOW
Both the precipitation and streamflow spectra show that there is a large power in the 6- and 12-month rainfall and runoff periods during the latter parts of the 31-year period [1970–2000]. The rest (72.2%) of the variability is due to other factors, mainly land use practices in the study area. Such sustained increase in current production is as a result of good rainfall as well as increased use of farm inputs.
S UMMARY
INTRODUCTION
C ONCLUSIONS
R ECOMMENDATION
INDIVIDUAL QUESTIONNAIRE
31 YEARS TIME SERIES DATA FOR FLOW OF THE NYANDO RIVER AT
