挑战包括划定含水层, mapping saltwater encroachment/ intrusion, 通过绘制含水层上面粘土覆盖层的变化来确定含水层的脆弱性, 地表水-地下水相互作用以支持管理含水层补给, 绘制垃圾填埋场的范围和来自垃圾填埋场的污染羽流, 绘制可能引发滑坡的粘土地图, 测绘和监测堤坝下的渗漏情况, and many more.
Geophysical methods are great tools to investigate subsurface hydrogeological parameters and processes in a cost-effective and minimally or non-invasive manner, and at relevant spatial scales. Ramboll has utilized geophysics for more than 35 years and gained extensive experience from numerous hydrogeological surveys around the world. These competences include designing geophysical surveys in different climate and geographical conditions, data processing and inversion, and very importantly interpretation of the geophysical data together with borehole information and other types of data to establish three-dimensional (3D) geological models.
An important task to achieve a successful geophysical project is a complete evaluation of the hydrogeological settings and subsequently selection of the most suited geophysical techniques. Ramboll has over the years developed a large and innovative geophysical toolbox that allow selection of the right tool for any specific survey.
Detailed knowledge of the general framework of the aquifers is extremely important when building numerical groundwater models and fundamentally to enhance groundwater management.
Managed Aquifer Recharge (MAR)
最近的气候变化导致了更多的极端天气事件. Regions characterized by moderate and frequent weather changes now experience longer periods of drought and short periods with extreme rain fall. MAR是一种收集雨水，渗透并储存在当地的方法. MAR的一个关键步骤是评估潜在的渗透地点. Geophysics provide very valuable information about where it is most suitable to infiltrate water and where the infiltrated water will flow.
In many geographical regions saltwater intrusion is a critical threat to the aquifers for domestic water supply. 因此，获取咸水入侵程度的信息是非常重要的. Electrical and electromagnetic geophysical investigations are ideally suited to provide this crucial information, 因为水的盐度对地下电导率有很强的影响.
含水层上方的粘土层可以捕获并减少农田中的硝酸盐. 因此，了解粘土层的范围和连续性是很重要的. Using geophysical methods, we can map variations within the clay cover and also point out area where the aquifers are vulnerable, i.e. 没有粘土覆盖(窗户)，含水层较少或不易破坏.
The desired depth of investigation, 分辨率和地质决定哪种地球物理方法最合适. The advantage of most geophysical methods is that they are non-invasive and leave none or minimal evidence on the ground. At the same time geophysical methods are truly in-situ methods since the ground is not disturbed by the measurement.
地球物理方法测量不同的地下性质. 通常测量的性质是电阻率或电导率和声速. The following is an introduction to a selection of the methods that are routinely employed at Ramboll.
Time-Domain Electromagnetics (TDEM)
Single site TDEM method has been used extensively in the last three decades for mapping the subsurface. 地面TDEM提供了地下电导率的点信息. It is common practice to conduct a TDEM survey by acquiring data at multiple points by which 3D distribution of electrical conductivity can be obtained. The depth of investigation depends on what system setup is used and electrical conductivity of the subsurface materials, and can be as large as 500 m.
For single site TDEM measurements Ramboll uses ProTEM from Geonics and the WalkTEM system from GuidelineGeo/ABEM.
Download TDEM Surveys (PDF) here.
Airborne ElectoMagnetics (AEM)
Airborne ElectroMagnetic (AEM) methods are efficient tools for large-scale investigations or in areas where ground access is limited. Helicopter-borne EM transient EM methods, such as SkyTEM, are developed specifically for accurate measurement of the electrical conductivity of the subsurface, which is vital in groundwater investigations where the variation of electrical conductivity is much less than its variation in mineral explorations.
Ramboll与SkyTEM Surveys ap在不同的AEM项目上有着丰富的合作经验. 利用SkyTEM系统，可以在短时间内以经济有效的方式绘制大面积的地图. Results obtained with the SkyTEM system are comparable with result from the TDEM soundings; however, 机载系统测量连续的剖面, thus much faster coverage. The depth of investigation varies depending on the system setup and the subsurface electrical conductivity, and can exceed 300 m.
Towed TEM (tTEM)
拖曳瞬变电磁(tTEM)是一种新型的瞬变电磁技术. With tTEM, large geographic areas can be mapped rapidly and with at a very high lateral and vertical resolution, down to a depth of ~ 60-80 m.
Floating TEM (FloaTEM)
Surface water- groundwater interaction is often a very important to describe the hydraulics of an aquifer as well as the river inflow. Similar to tTEM, 最近开发了一种用于水中快速数据采集的浮动TEM (FloaTEM)系统.
The NMR/MRS method is a method to directly estimate water content and permeability without a need for drilling. 核磁共振技术在地表和钻孔中都有应用. 核磁共振/MRS方法用于在几个可能的位置中优化井眼位置, to improve coverage of hydraulic parameters and to determine water content when designing dewatering or groundwater table lowering in construction projects.
Electrical Resistivity Tomography (ERT) is an electrical method to measure the electrical resistivity of the subsurface. Cables with multiple outtakes are laid out and current is injected to the subsurface by spears connected to the outtakes. 测量每对电极之间的电位电压差.
Using the entire data set, sections or profiles with detailed variation of the resistivity are obtained with an investigation depth of up to 150 m depending of the system setup. Ramboll使用了GuidelineGeo/ABEM公司的Terrameter LS仪器.
Ground Conductivity Meter (GCM)
The Ground Conductivity Meter (GCM) is a frequency-domain EM instrument used to obtain very dense and detailed information of the shallow subsurface, i.e. the top ~ 8 meters. Even in urban environments the GCM method has successfully been applied to identify suitable areas for infiltration from the surface and to compare different sites.
下载连续测量- DualEm421S (PDF).