GSI Groundwater Recharge Mapping

The national Groundwater Recharge Map depicts estimated recharge to the deep Groundwater system, i.e. Groundwater that can be tapped as the sustainable resource. The main hydrogeological controls on Groundwater recharge include subsoil permeability, subsoil thickness, saturated Soils, and the ability of the Underlying aquifer to accept percolating waters. Estimated Groundwater recharge is lowest in overlain areas by thick, low permeability clay. Where lower productivity aquifers underlie the land surface, a recharge cap is applied to simulate rejected recharge, even where subsoils are thin. This reflects the limited ability of these aquifers to accept and transmit recharging waters. The map is derived from existing hydrogeological and Meteorological data layers: annual rainfall, annual estimated actual evapotranspiration (AE), soil Drainage, subsoil permeability, Groundwater vulnerability, Peat, sand/gravel aquifer, Bedrock aquifer class. The layers are overlain and interpreted using the guidelines (GW 5) outlined by the Irish Working Group on Groundwater (WGGW, 2005), subsequently revised in Hunter Williams et al (2011) and Hunter Williams et al (2013). The combination of hydrogeological layers gives a particular hydrogeological scenario that is related to a recharge coefficient. The recharge coefficient is the proportion of effective rainfall that can potentially become recharge. The map of recharge coefficients is combined with the effective rainfall map and the recharge cap to produce the Groundwater recharge map. Utilities of the map include: aquifer water balance assessments using simple lumped models or distributed numerical Groundwater models; assessment of the impact of Groundwater abstractions as required under the European Water Framework Directive; and delineation of source protection Zones. Outer and inner ranges for the Groundwater recharge coefficients are defined, to be used depending on the hydrogeology of the study area. Users should be aware that the map uses the central value of the inner recharge coefficient range, and the 30 year average effective rainfall (1971-2000, Met Eireann). Setup, Groundwater recharge may be over- or under-estimated, depending on local conditions Users should also be aware that the recharge cap applied to poorly productive aquifers may need further examination for studies; that Karst aquifer resources may be overestimated due to low storage within these aquifers; that only diffuse recharge is modelled and point and allogenic recharge are not accounted for in the Groundwater recharge map; that the influence of the water table depth and ground Slope are not accounted for.国家地下水补给地图（Groundwater Recharge Map）描绘了深层地下水（Groundwater）系统的估算补给量，即可作为可持续资源开发利用的地下水。 影响地下水补给的主要水文地质控制因素包括下层土渗透性、下层土厚度、饱和土壤，以及下伏含水层（aquifer）接纳渗流水的能力。在被厚层低渗透性黏土覆盖的区域，地下水补给估算量最低。当地表下方为低产能含水层时，即便下层土较薄，也会设置补给上限以模拟被拒绝的补给量，这反映了此类含水层接纳和传输补给水流的能力有限。 该地图基于现有水文地质与气象数据图层生成，包括：年降雨量、年实际蒸散发估算值（AE）、土壤排水性、下层土渗透性、地下水脆弱性、泥炭层、砂/砾石含水层、基岩含水层分类。 数据图层的叠加与解译遵循爱尔兰地下水工作组（Irish Working Group on Groundwater, WGGW, 2005）制定的《GW 5》指南，该指南后续在Hunter Williams等人（2011）及Hunter Williams等人（2013）的研究中进行了修订。水文地质图层的组合可得到与补给系数相关的特定水文地质情景。补给系数指可潜在转化为补给量的有效降雨量占比。补给系数地图与有效降雨量地图及补给上限相结合，最终生成地下水补给地图。 该地图的用途包括：采用简单集总模型或分布式数值地下水模型开展含水层水平衡评估；依据《欧盟水框架指令（European Water Framework Directive）》要求评估地下水开采的影响；以及划定水源保护区。 地下水补给系数已定义内外两个区间，可根据研究区的水文地质情况选用。用户需注意，该地图采用了补给系数内部区间的中心值，以及1971-2000年的30年平均有效降雨量（爱尔兰气象局Met Éireann）。受当地条件影响，地下水补给量可能被高估或低估。 用户还需注意：针对低产能含水层设置的补给上限，在相关研究中可能需要进一步核验；由于岩溶含水层（Karst aquifer）的储水能力较低，其资源量可能被高估；该地图仅模拟了弥散补给，未考虑点补给与外源补给；同时未纳入地下水位埋深与地面坡度的影响。