ontwatering

Ontwatering, in English typically called dewatering, is the process of removing or lowering groundwater and surface water to create and maintain dry working conditions in soil. It is used during construction, mining, excavation, tunneling, and environmental remediation. The aim is to reduce hydrostatic pressure, prevent water inflow into a site, and control pore-water pressures to improve soil stability and allow equipment access and placement of structures.

Common methods include surface drainage, such as ditches or channels that redirect water away from the site; and sub-surface drainage with perforated drains, trench drains, and sumps to collect and remove infiltrating water. Pumping systems are central to ontwatering, using sump pumps, wellpoints, infiltration wells, or deeper dewatering wells to lower the water table. In some cases, combinations of drainage and pumping are used, sometimes supplemented by barriers or cut-off walls to limit groundwater inflow.

Design and execution require estimating the required drawdown, pump capacity, and the spacing and duration of pumping, often informed by pumping tests and aquifer properties. Discharge options include releasing water to surface water bodies, routing it to a treatment system, or reinjecting it into a suitable aquifer, all under regulatory oversight.

Applications span foundation and basement construction, road and rail tunnels, excavation for civil works, mining operations, and remediation projects where groundwater or perched water would hinder work. Environmental and regulatory considerations include controlling sediment and contaminants in discharged water, preventing impacts on nearby wells, and ensuring compliance with water quality and discharge permits.