Description
CHAPTER ONE
1.1 INTRODUCTION
Water is an integral part of life, as human beings derived from the
environment several services that are necessary for the survival, Water is one of
the basic needs that human beings cannot live without; indeed water is life!
Therefore, water-related (hydrological) ecosystem services provided by the
environment (e.g provision, regulation and purification of freshwater) are quite
valuable and important for human well-being. This underscores the importance
of sound watershed management for continued provision of hydrological
ecosystem services. From a hydrological point of view, a watershed includes all
land contributing water (surface and ground water) to a reference point.
It is therefore obvious that land comprising of any watershed would
generally be under other uses such as forests, agriculture and urban centers,
which might commonly be considered ‘primary’ land uses. This means that
watersheds provide other important ecosystem services, beside provision of
hydrological ecosystem services. In some cases, enhanced provision of some
ecosystem services may also lead to reduced capacity of watersheds to provide
other services e.g. intensive cultivation to maximize food production may also
lead to increase in soil erosion and consequently degradation of water quality.
Sediment yield is the amount at a point of interest in a particular period of time
which occur due to heavy rainfall, are normally as tones per year or kilogram per
year.
A large part of failure to achieve reasonable estimates of average annual
sediment lies in particles of extrapolating relationship derived from field data
with no consideration of appropriateness for future conditions.
Sediment yield is affected by many factors such as climate, soil, relief, vegetation
and human influence. Runoff refers to as the part of water cycle that flow over
land as surface water.
Runoff has been used as a variable representing climatic conditions and
includes not only the water that travel over the land surface and through
channels to reach a stream but also interflow, the water that infiltrates the soil
surface and travels by means of gravity toward a stream channel.
In this study offa water shed is simulated to predict the surface runoff and
sediment yield. The spatial and temporal variation obtained can be used as a
decision support tool in the management of the water shed.
1.2 PROBLEM STATEMENT
Recent flooding issues in Nigeria as a result of excessive rainfall has resulted into
runoff and sediment yield in the area. Therefore in order to manage the water
shed sustainability, it is necessary to predict the variation of sediment yield and
runoff in the area which can serve as a data base in managing the watershed.
1.3 AIM AND OBJECTIVES
The aim of the research was to investigate the spatial and temporal variation of
sediment yield and runoff in Offa watershed.Specific objectives achieved are:
i. Predict the surface runoff and sediment into watershed
ii. Develop temporal variation map of sediment yield and runoff
iii. Develop spatial variation map of sediment yield and runoff
1.4 JUSTIFICATION
The Spatial and temporal variation of sediment yield and runoff in the catchment
area can serve as a decision support tools to water managers in the area to plan
a sustainable management of the water shed.
1.5 SCOPE OF STUDY
The scope of the work was limited to the study of temporal variation of sediment
using temporal data of 31years from 1986 to 2016. the analysis was based on
preliminary modeling results obtained from digital elevation model (DEM) land
use and soil map to predict the optimum variation of sediment yield and runoff
generation in Offa water shed.
1.6 DESCRIPTION OF STUDY AREA
Offa water shed is located in offa local government area of kwara state
Nigeria. It is one of the main water supply in its locality, it is about 43km from
Ilorin the capital of kwara state it fall within the latitude 8.1393 o N and 4.7174 0 E.
The map is shown in figure 1.1-1.3