Nigerian Journal of Technology (NIJOTECH) Vol. 33 No. 4, October 2014, pp. 566 – 573 Copyright© Faculty of Engineering, University of Nigeria, Nsukka, ISSN: 1115 -8443 www.nijotech.com http://dx.doi.org/10.4314/njt.v33i4.18 RAINFALL RUNOFF MODEL FOR CALABAR METROPOLIS U SING MULTIPLE REGRESSION R. E. E. Antigha 1, *1, * , A. J. Akor 222, M. J. Ayotamuno 333, I. Ologhodien 444 and N. M. Ogarekpe 555 111,1,,, 555 DEPARTMENT OF CIVIL ENGINEERING , CROSS RIVER UNIVERSITY OF TECHNOLOGY , CALABAR , NIGERIA 222,2,,, 333 DEPT OF AGRICULTURAL AND ENV . ENG ., RIVERS STATE UNIV . OF SCIENCE AND TECH ., PORT HARCOURT , NIGERIA 444 DEPARTMENT OF CIVIL ENGINEERING , RIVERS STATE UNIV . OF SCIENCE AND TECHNOLOGY , PORT HARCOURT , NIGERIA EEE-E---mailmail addresses: 111 [email protected] , 222 [email protected], 333 [email protected] , 444 [email protected] , 555 [email protected], ABSTRACT Mathematical analyses were used to develop model that predicts the influence of some hydraulic and hydrologic parameters on the perennial flooding of some parts of the Calabar Metropolis. The parameters were obtained from ten sampling locations all within Calabar metropolis. An empirical model was developed to predict discharge based on the independent variables of cross sectional area of drains, degree imperviousness, g radient, sum of channel length, and basin area. The model developed gave a good multiple regression coefficient of 0.982with a standard error of 0.709at a significance level of 0.10. The R 222 value of the regression model shows that 96.4% of the total variation in the storm water discharge is accounted for by the five regressors. Incorrect sizing and spread of drains as well as the existing slopes employed in the generation of the drains’ inve rt during construction have been seen as some of the key factors that foster flooding in the Metropolis. Designers are encouraged to employ the model developed for drains design and analysis for Calabar Metropolis. Keywords: storm water, modeling, floodi ng, empirical, Calabar metropolis 1. INTRODUCTION damaging buildings, eroding the land and sometime s Man’s need to protect himself and his possession from causing landslides [1]. Also, very flat terrain leads to the threat of flood and erosion has remained one of low flow velocities which often result in flooding. the most important considerations in his struggle for In some parts of Calabar M etropolis, roads have been survival. Historically, m ost cities of the developing built by filling in channels. This has resulted in serious world sprang up along the coastal regions as ports, flooding. Where the natural drainage channels are not often on the estuaries of rivers which served as filled or obstructed by buildings, they often beco me commercial arteries. These coastal regions of the blocked by domestic refuse. On the other hand, tropics in which Calabar Metropolis is one of such, drainage improv ements in one area are closely linked have the highest averag e rainfall. However, due to the with drainage problems elsewhere. The current trend flat terrain and often alluvial soils, drainage is difficult. worldwide is towards urbanization . As a consequence, Large areas of impermeable surfaces and sparse urban problems associated with the hydrologic vegetation in the urban centres, coupled with aspects of water management should become inadequate drainage facilities, results in the formation increasingly more acute. Effective disposal of storm of excessive run-off within minutes of a storm event. water has become very essential. Urban storm water This, of course often results to damage to lives and management is no longer based on the interception, property. collection and disposal of storm water only, but also The lack of drainage is especially serious where the on the application of workable model approaches in ground is either steeply sloping or very flat. On very storm drainage designs. steep sites, as in parts of Luand a, Rio de Janeiro and Sound storm water design practices help to maintain Hong Kong, stormwater flows fast and violently, compatible drainage systems, minimize disturbance to * Corresponding author, Tel: +234+234----703703703703----878878878 ---2554-255425542554 RRRAINFALL RRRUNOFF MMMODEL FOR CCCALABAR MMMETROPOLIS USING MMMULTIPLE RRREGRESSION ,,, R. E. E. Antigha, et al existing drainage patterns, control flooding of caught up on foot or in their car by fierce and fast property, structures, and roadways, and minimize running waters on impervious roads or from storm environmental impacts of storm water runoff. water overflowing drainage systems whose storage Urbanization tends to increase downstream peak capacities have been exceeded. flows, runoff volumes, and runoff velocities. These A storm water drainage system is a sub-system of the changes can cause the capacity of adequately designed total urban water resource system. As such, storm downstream systems to be exceeded and disrupt water system planning and design for any new natural waterways. The impacts of new urbanization development must be compatible with watershed are expected to be reduced through the use of master plans and objectives, and must be coordinated structural and non-structural Best Management with plans for land use, open space, transportation, Practices (BMPs) that may include storm water and other community objectives. Watershed master detention. plan must consistently address storm quantity and In Calabar Metropolis, rapid and largely unplanned quality issues, as well as regional issues [3]. urban growth has, over the years, resulted in land use Storm water systems should be designed both to changes and modifications, which have resulted to provide adequate surface drainage and to meet other changes in the hydrological fluxes in the urban important storm water management goals, such as watershed. protection of water quality, stream channels, habitat Over the past thirty-six years, the area of impervious and groundwater. In addition, storm water surfaces in Calabar Metropolis has significantly management practices must strive to preserve and increased. This has resulted from the several activities promote the general health, safety and welfare of the of man to foster urbanization and expedite public. Storm water drainage is defined by watershed, development. In 1972 for instance, the city had an not by administrative jurisdiction, and therefore area of about 120.8sqkm. At the end of 2006 however, requires co-operative efforts on a watershed basis to the area had expanded to encompass not less than be implemented effectively. The aim of this study is to 480sqkm, [2]. As urbanization continues, there is develop a rainfall runoff model for Calabar metropolis increased population density. This means that more using the multiple regression approach. To this end, areas have been devoted to housing and businesses. the specific objectives are as follows: This in turn results in an increase in the area of a. Identify the pertinent factors or variables of the ground covered with impervious surfaces. This drainage systems of Calabar Metropolis. should also mean that a good portion of the right-of- b. Develop a multiple regression model based on way of water, specifically overland flow, have been these factors. tampered with. Accordingly, as there are more impervious surfaces in the ever-spreading urban area, 2. MATERIALS AND METHODS threat of flooding is bound to increase during any 2.1 Description of Area of Study major storm event. This should be expected because Calabar Metropolis lies between latitudes 04 45’ 30” water runs off quickly and there is an increase in peak North and 05 08’30” North of the Equator and discharge rates. This, of course overwhelms the longitudes 8 11’ 21” and 8 30’00” East of the various hydraulic structures and systems across the Meridian. The town is flanked on its eastern and entire metropolitan area. western borders by two large perennial streams viz: Parts of the southern part of Calabar Metropolis has the Great Kwa River and the Calabar River been built through the common practices of land respectively. These are aside from the numerous reclamation such as artificial landfill of depressions, ephemeral channels which receive water after storm back filling swamps, wetlands and floodplains. These events to drain the area of study. practices, coupled with the inadequacy of drainage The Calabar River is about 7.58 metres deep at its two network, reduce the flood storage and overwhelm the major bands [4]. The city lies in a peninsular between carrying capacity of existing channelsthereby the two rivers, 56km up the Calabar River away from increasing urban storm throw-up during storm events the sea. Calabar has been described as an inter-fluvial in the metropolis. settlement [5]. In Calabar Metropolis, the dwellers are aware of the The area is drained by the two main perennial problems of urban storm water, but have no power channels, the Calabar and the Great KwaRivers. The over it. Some of them do not know what to do when Nigerian Journal of Technology, Vol. 33, No. 4, October 2014 567567567 RRRAINFALL RRRUNOFF MMMODEL FOR CCCALABAR MMMETROPOLIS USING MMMULTIPLE RRREGRESSION ,,, R. E. E. Antigha, et al rivers are fed by the numerous ephemeral and (a). Collection of data such as storm and run -off intermittent channels, gullies and rills which are events, land-use conditions, soil and vegetation inundated during the slightest storm events. Surface details for Calabar Metropolis as well as a contour water i s also carried by the sloping terrain, the crenulations in order to observe the morphology roadside ditches and sandy soils which are pervious to of the drainage basin. water. The major ephemeral channel is the one (b). Analyses of these collected data truncating the city from the MCC/WAPI junction axis (c). Selection of suitable storm events of the study down to the Cross River University of Technology staff catchments for model parameter calibration quar ters on the south, and empting roughly and Data for this work were acquired from two sources.