Group 7 (Groundwater and Subsurface Flow )

subsurface flow

begins in The Zone of Aeration (Vadose Zone) , which is the layer of soil directly beneath the surface but above the water table.

Where it starts: It begins in the topsoil and the subsoil layers.

top soil [ o and a horizons ]

is the uppermost layer of the soil profile, usually extending about 5 to 10 inches deep. It is the most biologically active layer.

sub soil [ b horizon ]

is a more compact layer that acts as a transition zone toward the bedrock

groundwater

officially begins at the Water Table, which is the top boundary of The Zone of Saturation (Phreatic Zone).

Where it starts: It begins deep enough underground where all the spaces between rocks and soil are 100% filled with water.

How it starts: It is the result of deep percolation. Water travels vertically through the vadose zone until it hits the existing water table

water table

is the specific surface that separates the Zone of Aeration from the Zone of Saturation. It is often described as the "top" of the groundwater.

aquifers

is a geological formation that can store, transmit, and yield groundwater in sufficient quantities for use. It is composed of permeable materials such as sand, gravel, or fractured rock, which allow water to move through pore spaces or cracks.

types of aquifers

• unconfined

• confined

• perched

unconfined aquifers

Located near the surface with no confining layer; directly recharged and more prone to contamination.

confined aquifers

Bounded by impermeable layers; water is under pressure and less exposed to pollution

perched aquifers

A small, localized aquifer above the main water table temporary and limited in supply

porosity

is the measure of the void spaces (pores) within a material, expressed as a percentage of the total volume. It indicates how much water an aquifer can store

permeability

refers to the ability of a material to allow water to pass through it via connected pore spaces.

hydraulic conductivity

is the measure of how easily water can move through an aquifer material under a hydraulic gradient. It combines the effects of permeability and fluid properties (like viscosity).

properties of aquifers

• porosity

• permeability

• hydraulic conductivity

importance in water supply

• source of freshwater

• agricultural support

• industrial use

• drought resilience

• ecosystem support

groundwater movement

refers to the flow of water through the pores and fractures in soil and rock beneath the ground surface

types of subsurface

• unsaturated zone

• saturated zone

unsaturated zone

where pores contain both air and water

saturated zone

where all pores are filled with water (groundwater zone)

hydraulic gradient

is the main driving force behind groundwater movement. It represents the change in hydraulic head (water level or energy) over a certain distance

formula of hydraulic gradient

i = Δh / L

flow processes

• infiltration

• percolation

• seepage

infiltration

is the process by which water on the ground surface enters the soil.

percolation

is the downward movement of water through soil and porous materials after infiltration.

seepage

is the slow movement of water through soil or porous materials, often visible at the surface.

recharge areas

are locations where water enters the groundwater system.

• Usually found in higher elevation

• Water infiltrates and percolates downward to replenish aquifers

• Examples: forests, open fields, and permeable soils

discharge areas

are locations where groundwater emerges back to the surface.

• Occur in lower elevations

• Water exits through springs, rivers, lakes, or wells

• Examples: wetlands, streams, and coastal zones

darcy’s law equation

is the fundamental equation governing the flow of fluid through a porous medium (such as soil or rock). Formulated by Henry Darcy in 1856 based on experiments with sand filters

formula of darcy’s law equation

Q = k i A

application in real life

• dam seepage analysis

• aquifer management

• contaminant transport

• foundation drainage

limitations of darcy’s law

In very coarse materials (like large boulders) or under extremely high pressure where flow becomes turbulent, the linear relationship between velocity and gradient no longer holds true.

engineering applications

• well systems

• dewatering

• foundation stability

engineering problems/issues

• depletion and subsidence

• contamination

• saltwater intrusion

management solution

• conservation

• artificial recharge