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    【Rainfall-Runoff,Simulation,in,Part,of,Lower,Niger,Basin】cut off什么意思

    来源:六七范文网 时间:2019-04-25 04:55:10 点击:

      Abstract: Water resources assessment in poorly gauged and ungauged basins demand supportive rainfall-runoff estimation, while resolving practical water resource management and planning issues. In this study, the research method employed involves rainfall-runoff modeling and simulation with proper efficiency criteria evaluation using the MODMENS modeling platform, a numerical rainfall-runoff semi-distributed GR2M conceptual lumped model. The rainfall-runoff simulation was carried-out in three selected sub-basins of Lower River Niger Basin based on observable discharge dataset. Related error estimation was carried-out to estimate the runoff simulation uncertainty while model optimization approach entails use of Rosenbrock-Simplex method and model reliability evaluation entails the use of Nash and Sutcliffe efficiency criteria methods. Result shows a satisfactory model performance at Baro and Makurdi gauging stations (savannah ecological zone) while under-estimation characterizes simulated flow at Onitsha gauging station (Forest ecological region). Seasonally, the model best fit the dry season flow but underestimate during the high flow periods (rainy seasons and wetter years).
      Key words: Rainfall-runoff, simulation, GR2M, River Niger.
       1. Introduction
      Rainfall-runoff modeling plays an important supportive decision role in resolving practical water resource management and planning issues. This is usually carried-out with a degree of uncertainty in their predictions through approximation of the real-world system. The approximation is a complex activity being influenced by series of implicit and explicit factors, such as the drainage basin and storms event characteristics [1-3].
      The approximation technique entails models development and applications which have been the basis of hydrological research for advancement in knowledge and understanding of the hydrological processes involved in the rainfall-runoff transformation. It also provides practical solutions to many of the related environmental and water resources management problems. The predictive ability of such model necessitates enrichment of existing models and development of new ones from the vantage of advancement in computing and information technology which allowed the storage and processing of large volume dataset series. Simple runoff model facilitates systemic uncertainty assessments and can fit stream-flow data as well as more complex structures [4].
      Water resources related issues in Lower Niger River Basin include dearth of data, inconsistent dataset, inadequate hydrological monitoring and poor data bank management network, among others. Present state of the gauging equipment and gauging stations is also deplorable with increasing cases of complete abandonment [5]. This has resulted into varied degree of water resources planning and management problems within the river basin with a lot
      of socio-economic constraints. Thus, in this study rainfall-runoff relationship and dynamics within Lower Niger River system was carried-out with emphasis on three sub-basins within the system (Baro, Makurdi and Onitsha). The analysis involves the use of a semi-distributed conceptual model that incorporates a water balance concept. This is in an attempt to generate useful hydrological information for purposeful water resources planning and management within the data-scare river system as well as investigating the adequacy of MODMEMS application for rainfall-runoff estimation within the river basin. with discharge contribution of about 117 km3/year, this constitute about 64.3% to the total River Niger flow [6]. Flow in the Lower Niger region substantially increases downstream Lokoja after confluence with River Benue, with several tributaries and flows southward before emptying through the Niger Delta, an area characterized by swamps, lagoons, and navigable channels. Mean inter-annual discharge of the Niger upstream of Jebba and downstream of the Kainji and Jebba dams is 1,454 m3/s. Following the confluence at Lokoja, the flow increases to 5,660 m3/s(mean for the period 1915-2001). Niger River Basin system has a drainage basin of 2,117,700 km2 with annual population growth rate of 3%, which largely depend on the river for their livelihood. The estimated population is about 104.5 million (80% of which is in Lower Niger section) and will likely double by 2025[6].
      In addition, over the years the Lower Niger has been experiencing marked decrease in flow with mean flow of 6,055 m3/s (191 km3/year) for 1929-1970 compared to 5,066 m3/s (160 km3/year) for the
       regression) [14]. It is a measure of statistical association, which indicates the percentage of the observed variance as explained by the predicted data, in order to assess the model fitness of available observations, i.e., objective or efficiency criteria.
      Nash and Sutcliffe efficiency criterion is quantatively defined as one minus the sum of the absolute squared differences between the predicted and observed values normalized by the observed values variance [15].
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      RE (2)
      Present water developmental needs, especially in the developing countries where cases of poorly and ungauged basins abound demands, among others, adoption of a verifiable synthetic hydrology approach. Thus, this study adopted the use of a semi-distributed conceptual model that incorporates a water balance concept to investigate the rainfall-runoff relationship and the model adequacy and application within three sub-basins (Baro, Markurdi and Onitsha) within the data-scare Lower Niger River system.
      Although, the model satisfactorily best fit low periods and flow within the gauging stations located in savannah ecological zones. The use of MODMENS software provides an easy applicable tool towards predicting flow based on rainfall-runoff relationship, in the 3 sub-basins within lower Niger Basin.
      Finally, there is a need for more scenario building with additional sub-basins within the Lower Niger system and detailed estimation of the evapotranspiration process of the water balance component and its functional relationship with the other simulated processes. Such estimation is necessary to fully quantify the varied system storages component.

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