Subsidence — dewatering depth 0.5 meters

Subsidence in South Holland has a very strong connection with water management. As a result, it is not possible to make realistic predictions of the subsidence over longer periods. Instead, soil subsidence sensitivity has been mapped. For this, it has been calculated how much peat oxidation and clink would theoretically occur over a period of 100 years, with a fixed dewatering depth of 1 m and maintaining the current elevation in the first aquifer package. Three classes were then made of the calculation results: ‘not relevant’, ‘relevant’ and ‘special focus area’. The classes reflect variations in the structure of the subsurface. Where sand is mainly found, subsidence is not relevant. In clay and peat areas subsidence plays an important role. Clay areas and areas with a relatively thin peat layer fall into the ‘relevant’ class. The “special focus area” covers the ten percent of the provincial land area with the greatest subsidence sensitivity. These are mainly areas with a thick peat layer. The map for soil subsidence shows that a large proportion of peat meadows, from the topic of soil subsidence, require special attention in design and water management. This is especially true for those areas where peat is directly on ground level and is not covered by clay (e.g. parts of Central Delfland, Alblasserwaard, Krimpenerwaard, the area between Gouda and Boskoop and around the Nieuwkoopse Plassen). In the dryhouses around Zoetermeer, the peat has disappeared due to dyeing and soil subsidence is less relevant. Also along the Oude Rijn, on the South Holland islands and in a wide zone along the North Sea coast, with the exception of the lowlands between the beach walls, subsidence is not relevant. After this, three scenarios of subsidence are shown at a fixed dewatering depth of 0.5, 1.0 and 1.5 m. From the scenario with a fixed dewatering depth of 1.0 m, the soil subsistence map is distilled. The three scenarios provide insight into the dependence on soil subsidence for fed water management. It can be seen, for example, that at a depth of 1.5 m the area with a subsidence of more than 10 mm/year is more than twice as large as at a dewatering depth of 0.5 m. At the time of zooming in on a specific area or demand, it should always be examined whether further information is available.荷兰南荷兰省的地面沉降与水利管理关联极为紧密。正因如此，无法对较长时段内的地面沉降做出贴合实际的精准预测。为此，研究团队转而开展了土壤沉降敏感性制图工作。本次计算设定固定排水深度为1米，并维持第一含水层组的当前高程，推演了100年理论上的泥炭氧化与固结过程的发生量。据此将计算结果划分为三类："不相关""相关"与"重点关注区域"。该分类反映了地下结构的差异：若地层以砂质为主，则地面沉降不相关；在黏土与泥炭分布区域，地面沉降影响显著。黏土区域以及泥炭层相对较薄的区域归入"相关"类别；"重点关注区域"则涵盖了省内陆地面积中沉降敏感性最高的10%区域，这类区域大多分布有厚层泥炭。土壤沉降地图显示，大量泥炭草甸在设计与水利管理工作中需要重点关注，尤其是那些泥炭直接出露于地表且无黏土覆盖的区域，例如代尔夫特兰中部部分区域、阿尔布拉瑟瓦尔德、克林珀讷瓦尔德、豪达与博斯科普之间的区域，以及新科普斯普拉斯周边区域。在佐特梅尔周边的干燥垦区，泥炭已因排水作用消失，地面沉降相关性较低。此外，沿老莱茵河（Oude Rijn）、南荷兰省各岛屿以及北海沿岸的广阔区域（海堤间的低地除外），地面沉降均不相关。随后，本次研究展示了三种固定排水深度下的沉降情景：0.5米、1.0米与1.5米。其中，基于1.0米固定排水深度的情景，衍生出了土壤沉降地图。这三种情景可帮助理解水利管理对地面沉降的依赖关系。例如，当排水深度为1.5米时，年沉降量超过10毫米的区域面积是排水深度0.5米时的两倍以上。在针对特定区域或需求进行放大查看时，需始终核查是否有可用的补充信息。