GroMoPo Metadata for Coastal Nethrlands MOCDENS3D model

Climate change in combination with increased anthropogenic activities will affect coastal groundwater systems throughout the world. In this paper, we focus on a coastal groundwater system that is already threatened by a relatively high seawater level: the low-lying Dutch Delta. Nearly one third of the Netherlands lies below mean sea level, and the land surface is still subsiding up to 1 m per century. This densely populated delta region, where fresh groundwater resources are used intensively for domestic, agricultural, and industrial purposes, can serve as a laboratory case for other low-lying delta areas throughout the world. Our findings on hydrogeological effects can be scaled up since the problems the Dutch face now will very likely be the problems encountered in other delta areas in the future. We calculated the possible impacts of future sea level rise, land subsidence, changes in recharge, autonomous salinization, and the effects of two mitigation countermeasures with a three-dimensional numerical model for variable density groundwater flow and coupled solute transport. We considered the effects on hydraulic heads, seepage fluxes, salt loads to surface waters, and changes in fresh groundwater resources as a function of time and for seven scenarios. Our numerical modeling results show that the impact of sea level rise is limited to areas within 10 km of the coastline and main rivers because the increased head in the groundwater system at the coast can easily be produced though the highly permeable Holocene confining layer. Along the southwest coast of the Netherlands, salt loads will double in some parts of the deep and large polders by the year 2100 A.D. due to sea level rise. More inland, ongoing land subsidence will cause hydraulic heads and phreatic water levels to drop, which may result in damage to dikes, infrastructure, and urban areas. In the deep polders more inland, autonomous upconing of deeper and more saline groundwater will be responsible for increasing salt loads. The future increase of salt loads will cause salinization of surface waters and shallow groundwater and put the total volumes of fresh groundwater volumes for drinking water supply, agricultural purposes, industry, and ecosystems under pressure.气候变化与日益加剧的人类活动将共同影响全球范围内的海岸地下水系统。本研究聚焦于一个已受相对偏高海平面威胁的海岸地下水系统——低洼荷兰三角洲（Dutch Delta）。荷兰近三分之一的国土海拔低于平均海平面，且地表仍以每百年最多1米的速率持续沉降。这片人口稠密的三角洲区域内，地下淡水被广泛应用于生活、农业与工业领域，可作为全球其他低洼三角洲地区的典型研究案例。由于荷兰当前面临的问题极有可能成为未来其他三角洲地区即将遭遇的困境，本研究关于水文地质效应的结论具备可推广性。本研究采用变密度地下水流与溶质运移耦合三维数值模型（three-dimensional numerical model for variable density groundwater flow and coupled solute transport），模拟了未来海平面上升、地面沉降、补给条件变化、天然盐渍化以及两种缓解对策的潜在影响。本次研究针对七种情景，分析了上述因素对水头、渗流通量、地表水盐负荷以及地下淡水资源随时间变化的影响。本次数值模拟结果显示，海平面上升的影响仅局限于海岸线与主要河流周边10公里范围内，原因在于海岸地下水系统的水头升高可通过高渗透性的全新世隔水层（Holocene confining layer）快速传递。到公元2100年，荷兰西南沿海部分大型深层圩田的盐负荷将因海平面上升翻倍。在更靠内陆的区域，持续的地面沉降将导致地下水头与潜水位下降，进而可能对堤防、基础设施与城区造成破坏。在更靠内陆的深层圩田中，深层高矿化地下水的自然锥进将导致盐负荷上升。未来盐负荷的增加将引发地表水与浅层地下水盐渍化，并将对用于饮用水供应、农业生产、工业活动以及生态系统的地下淡水资源总储量造成压力。