During the last five decades, the forests and natural resources have been highly disrupted by human activities, causing a significant decrease of the plant coverage, consequently resulting in an increase runoff and soil erosion. Likewise, since 1989 non-basic information related to these topics has been obtained from the field, which does not allow appropriate hydraulic structure design. The purpose of the current paper is to determine the relation between the Curve Number CN and runoff coefficient C, from information of the 34 meteorological stations located in the Manabi Hydrographic Demarcation (MHD), during the period 1963-2013. This work is developed using information provided by several State institutions, and support of Geographic Information System. The information is processed using lineal correlation analysis to find an equation that relates the CN a C values.

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Manabi is the only province in Ecuador that does not receive contribution of the runoff coming from the thaw of the snow-covered of the Andes mountain. This situation impacts severely on the agriculture activities. This study presents an estimate of water supply and demand of the Manabi hydrographic demarcation based on the hydro meteorological data and the water needs of the population by 2050. The research topic is very topical since it contributes to providing the necessary inputs for the planning and use of water resources in order to generate projects that tend to cover the current water deficit. The methodology used to estimate the water supply is based on the precipitation-runoff model proposed by the Soil Conservation Service of the United States of America. In fact, in spite of the annual volume of runoff has been estimated at 9658.83 hm3, against 2388.93 hm3, which is the average annual volume of water to meet the demands, from July to November it can be seen that the deficit reach at 330.27 hm3. The results obtained constitute a valuable tool for specialists and governmental and non-governmental institutions responsible for the control, planning and development of water resources in the region.