Influence Of Hydrologic & Sediment Parameters In Modeling Stream Flow
(A Case Study Of Osun River, Osun State Nigeria)
Understanding the dynamics of stream flow requires comprehensive consideration of hydrologic and sediment parameters, which play pivotal roles in accurate modeling. Hydrologic parameters encompass factors such as precipitation patterns, evapotranspiration rates, soil moisture content, and land use characteristics, all of which significantly impact water availability and runoff generation. Similarly, sediment parameters, including soil erodibility, topographic slope, land cover type, and sediment transport capacity, are crucial for assessing sediment yield and stream morphology alterations. Integrating these diverse parameters into stream flow models enhances their predictive capabilities, enabling more precise simulations of flow patterns, flood events, and sediment transport processes. By optimizing the representation of these hydrologic and sedimentary complexities, researchers can better inform water resource management strategies and mitigate the impacts of natural hazards like floods and sedimentation in fluvial environments.
INTRODUCTION
1.1 Background to the study
The water is the most important natural resource especially in the arid or semi-arid zones that face high population growth, scarcity of freshwater, irregularity of rain- fall, excessive land use change and increasing vulnerability to risks such of drought, desertification and pollution. Thus, the availability and the sustainable use of this resource become the core of the local and national strategies and politics in these regions.
Hydrology is the main governing backbone of all kinds of water movement and hence of water-related pollutants. Understanding the hydrology of a watershed and modeling different hydrological processes within a watershed are therefore very important for assessing the environmental and economical well-being of the watershed. These models can offer a sound scientific framework for watershed analyses of water movement and provide reliable information on the behavior of the system.
The degradation of hydrological resources has made it essential to encourage management practices based on knowledge of spatial and temporal changes in the quantity and quality of water, in order to ensure the suitability of water supplied for different uses. This can be assisted by using hydrological and water quality models to simulate a wide range of processes in hydrographic basins, such as the production of water and sediments and the dynamics of point and nonpoint sources of pollution.
Hydrological models are powerful tools to represent water-resource availability and behavior in drainage basins under many applications, such as climate change, flood, drought, runoff and nutrient movement (Abbaspour et al., 2015). They can assist in the planning and decision-making processes for environment protection and the guarantee of water availability for future uses (Da Silva et al., 2015; Fatichi et al., 2016).
The ability of hydrological model to produce satisfactory predictions is necessarily correlated to adequate sensitivity analysis and model calibration (Song et al., 2015). Hydrological models, such as SWAT, incorporate several parameters (climatic, hydrological and others) obtained theoretically and through field data collection. Some of these contribute greatly to model outputs (sensitive parameters), while others have minor relevance (non-sensitive parameters) (Van Griensven et al., 2006).
Osun is a river that flow southward through southern Nigeria into Lagos lagoon and Atlantic Gulf of Guinea. It is one of the several rivers ascribed in local mythology to have been women who turned into flowing waters after some traumatic event frightened or angered them. Osogbo GPS coordinates are 7˚46’15.74’’N and 4˚33’25.13’’E. Due to the potential of Osun river basin as a major source of water supply, this study will develop a plan that will allow for the sustainable management and treatment of the water in the catchment area.
1.2 Problem Statement
Osun River Catchment main source is one of the major sources of water supply, drinking and commercial purposes. It therefore important to know sensitive hydrologic parameters that contribute and hinder the stream flow out and sediment concentration in the catchment area.
1.3 Aims and Objectives
The main aim of this project is to investigate the use of modeling tool for sensitivity analysis of stream flow hydrologic and sediment parameters. Specific objectives achieved are:
i. Simulation of the hydrological process of the watershed using temporal and spatial data.
ii. Prediction of the stream flow and sediments yield of the watershed.
iii. Determine the influence of the hydrologic and sediment parameters on stream flow and sediment yield prediction.
1.4 Justification
Most rivers are ungauged especially in developing countries and therefore prediction of stream flow for sustainable water management is regarded as an alternative. Prediction of stream flow and sediment yield requires many hydrologic and sediment parameters. Also, calibrating and validating such models are quite cumbersome due to many parameters to deal with.
Therefore, it is very important to carry out sensitivity analysis of the modeling parameters to assist modelers in concentrating effort on most sensitive parameters that affect prediction of stream flow and sediment yield.
1.5 Scope of the Study
This research work is to carry out the sensitivity analysis of hydrologic parameters in modelling stream flow of osun river catchment. The analysis will be based on preliminary modelling results obtained from the modelling of the watershed. Parameters of interest are stream flow out and sediments yield with 31years meteorological data for the modeling exercises.
Model calibration and validation were not part of the scope covered in this research work.
1.6 Description of the Study Area
Osun is a river that flow southward through central Yoruba land in southern Nigeria into Lagos lagoon and Atlantic Gulf of Guinea. The Osun River is located within Osogbo Local Government Area of Osun State, Nigeria. It falls within Longitude 7˚46’15.74’’N and latitude 4˚33’25.13’’E. It is one of the several rivers ascribed in local mythology to have been women who turned into flowing waters after some traumatic event frightened or angered them. The map of the study area is as shown in Figure 1.1
Figure 1.1 Map of Nigeria show location of the Study Area
Influence Of Hydrologic & Sediment Parameters In Modeling Stream Flow:
Hydrologic and sediment parameters play a crucial role in modeling stream flow. The accurate representation of these parameters is essential for understanding and predicting the behavior of rivers and streams. Here are some key hydrologic and sediment parameters that influence stream flow modeling:
- Precipitation:
- Precipitation is a fundamental input in hydrological modeling. The amount, intensity, and distribution of precipitation events directly affect stream flow. Different modeling approaches consider precipitation in various ways, such as rainfall-runoff models that simulate the transformation of precipitation into runoff.
- Land Use and Land Cover:
- Land use and land cover influence the hydrologic cycle by impacting factors such as infiltration, evaporation, and surface runoff. Urbanization, deforestation, and agricultural practices can alter the natural flow patterns of rivers and streams. Land use data is often incorporated into hydrological models to account for these changes.
- Soil Properties:
- Soil characteristics, including soil type, porosity, permeability, and moisture content, affect the infiltration capacity and water retention of the soil. Hydrologic models consider these properties to simulate how water moves through the soil and eventually contributes to stream flow.
- Topography:
- The topography of the watershed, including elevation, slope, and aspect, influences the spatial distribution of precipitation, runoff, and sediment transport. Digital elevation models (DEMs) are commonly used in hydrological modeling to represent the topography of the study area.
- Vegetation:
- Vegetation plays a role in controlling evapotranspiration rates, interception of rainfall, and root structure that affects soil stability. Changes in vegetation cover can impact stream flow by altering the balance between infiltration and surface runoff.
- Channel Geometry:
- The characteristics of the river channel, such as its width, depth, and sinuosity, influence the flow velocity and capacity. Channel geometry is crucial in determining how efficiently a river can convey water and sediment downstream.
- Hydraulic Roughness:
- Manning’s roughness coefficient is a parameter used to represent the resistance to flow within a channel. It depends on channel characteristics, including vegetation, bed roughness, and channel shape. Proper estimation of hydraulic roughness is important for accurate stream flow modeling.
- Sediment Transport:
- Sediment parameters, such as sediment size distribution, sediment concentration, and transport capacity, are critical for modeling sediment transport in rivers. Sediment transport models are often coupled with hydrologic models to simulate the movement of sediment through the river system.
- Climate Variability:
- Long-term climate patterns and variability, such as El Niño and La Niña events, can significantly impact precipitation and temperature patterns. Climate influences hydrological processes and can lead to variations in stream flow.
- Human Activities:
- Anthropogenic activities, such as dam construction, water abstraction, and land use changes, can have a profound impact on stream flow. Modeling studies often consider the influence of human activities on the hydrological cycle.
In summary, incorporating accurate and representative hydrologic and sediment parameters into stream flow models is essential for producing reliable predictions and understanding the complex interactions within a watershed. Field measurements, remote sensing data, and hydrological models are often used in combination to estimate these parameters and enhance the accuracy of stream flow simulations.