Groundwater recharge restauration in urban area using Low Impact Development/Best Practices

Abstract

            In recent decades, urban population growth in Africa, Asia and Latin America is changing on an important rate and scale. The urban development is causing changing in surface runoff and groundwater recharge by modifying the existing mechanic. Urbanization increases the impervious area, which tends to lower the evaporation and direct infiltration of rainfall but increases surface runoff. This does not only influence the direct rainfall infiltration rate but also some urbanization practices cause water quality degradation such as increase of nitrogen, salinity, TDS and faecal contamination.Most of countries in arid and semi-arid regions have their water supply system relying on groundwater resource, this make the resource more important and its protection and conservation require particular attention. In areas where groundwater resource is threatened by urban development combined with climate change, Low Impact Development/best practices (LID/BP) are required for storm water treatment and infiltration, to increased direct deep infiltration of rainfall, better management of surface water which in turn can affect groundwater discharge or recharge.            LID has emerged recently in the last 30 years, it is promoted as suitable management practice for stormwater in urban area. Its purpose is to restore water balance in the postdevelopment site to the predevelopment conditions. LID stormwater management practice use in urbanized catchment could help to restore or increase groundwater recharge and help mitigate water scarcity issues. Many researches have investigated the effect of LID practices on surface water resource for better management but few of them has investigated the effect of LID stormwater management feature on groundwater recharge.              The southern coastal sedimentary basin of Benin is recently under a demographic pressure, impervious area is increasing due to constructions and the water use is increasing proportionally to the population growth. In the region, more than 87% of the population is supplied with groundwater resource. The present study has coupled SWMM with groundwater flow model MODFLOW to investigate the influence of LID practices on groundwater recharge in the study region which is under a residential development. The hydrologic model SWMM was used to estimate groundwater recharge, the infiltration was then used to evaluate the potential effect of the development on groundwater availability. The main goal of this study is to produce a numerical model that can be used to evaluate the deficit groundwater recharge caused by a site development in the southern region of Benin and design LID structure to restore groundwater recharge as in predevelopment conditions. The study has also attempted to develop an excel sheet which will be used for groundwater recharge estimation in specific regions of Benin and the developed database can be used to estimate groundwater recharge deficit caused by a site development.