Basic groundwater ideas include aquifers, water table, and steady flow—used before detailed well or dewatering design.

Scope (groundwater — basic)

This page introduces porous-media flow at a simple level: hydraulic head, unconfined and confined aquifers, and Darcy's law as a link between gradient and seepage velocity. In South Africa, site investigations and testing often follow SANS 3001 geotechnical methods; groundwater use and protection fall under DWS licensing and NEMA. Use field and lab k from the investigation report—this page is introductory and does not replace a groundwater model or legal compliance assessment.

Darcy check (concept)

  1. Define the flow direction and representative hydraulic gradient i (head drop per length).
  2. Select permeability k consistent with soil/rock type and test scale (lab vs pumping test).
  3. Compute v = k i for an order-of-magnitude seepage velocity (laminar regime).
  4. For 2D/3D heads, wells, or capture zones, use groundwater modelling software calibrated to site data.

Hydraulics & Hydrology — Groundwater (Basic Level)

Water in soil and rock: heads, aquifers, and steady seepage described by Darcy's law.

Introduction

Groundwater occupies voids below the water table (unconfined) or under pressure in confined aquifers. Engineers use hydraulic head maps and Darcy's law (v = k i) when flow is laminar through the porous matrix. Pumping tests and numerical models extend this to transient drawdown and well interference.

The calculator below applies v = k i with your chosen gradient and permeability.

Cross-section of confined and unconfined aquifers with wells and water table
Confined and unconfined aquifers (schematic). See licence on Wikimedia Commons
Diagram of water table following ground surface with a well
Water table and well (unconfined conditions). See licence on Wikimedia Commons

What basic groundwater concepts support

  • Scoping dewatering and seepage into excavations.
  • Order-of-magnitude flow for containment and remediation concepts.
  • Communication with hydrogeologists on heads, aquifers, and monitoring.
  • Input to geotechnical effective-stress and slope analyses.

Standards and regulation (South Africa)

Testing and reporting: SANS 3001 geotechnical series as cited in the project. Groundwater licensing and resource protection: DWS requirements. Environmental authorisations: NEMA and relevant listed activities. Always align with the groundwater specialist report for the site.

Darcy (1D):   v = k i   (laminar flow in porous media).

Notation (common)

  • k — hydraulic conductivity (permeability), often m/s.
  • i — hydraulic gradient (−dh/ds along flow).
  • v — Darcy (discharge) velocity (not average pore velocity unless divided by porosity).
  • h — total hydraulic head; z — elevation head.

Examples in practice

  • Excavation beside a river: estimate inward seepage for sump sizing.
  • Landfill liner: check gradient-driven leakage order of magnitude.
  • Water supply borehole: conceptual unconfined vs confined response.
  • Irrigation: saltwater intrusion risk in coastal aquifers (advanced studies).

Calculator — Darcy velocity

Enter k (m/s) and i (positive); output is v = k i (m/s).

v = k i

v = k i

Darcy seepage velocity v = k i from hydraulic conductivity and hydraulic gradient.

Key terms

Aquifer
Formation that stores and transmits significant water.
Piezometric head
Elevation of water level in a piezometer (confined aquifer).

Software and groundwater modelling

Regional and site-scale studies use finite-difference or finite-element groundwater models. Examples (official sites):

  • USGS MODFLOW — reference groundwater flow modelling.
  • Aquaveo GMS — graphical MODFLOW interface and workflows.
  • DHI FEFLOW — finite-element groundwater and heat/mass transport.
  • DHI MIKE — integrated surface–groundwater tools where applicable.
  • gINT — borehole and test data for parameter selection.

No product endorsement—boundary conditions, layers, and calibration must match investigation data. The Darcy calculator is a 1D steady check only.

Diagram sources

Educational schematics. Files in Images/groundwater-basic-level/ were downloaded from Wikimedia Commons into this repo (not copied from other topic folders). Confirm licence on each Commons file page before reuse.