Infiltration gallery – Uses, Construction, Formula and Difference between infiltration gallery and infiltration well

What is an infiltration gallery?

An infiltration gallery is the source of water at the subsurface level used as a water supply system. Its structure looks like a horizontal drain that is situated below the water table so that it can collect groundwater. It collects subsurface sources of water.

This horizontal drain is rather made up of open jointed pipe or perforated pipe. And after collecting water at the end it is taken to the sump or a collecting well from where it can be pumped out.

Infiltration gallery definition: Infiltration gallery is a horizontal drain structure made from open jointed pipe or perforated pipe, or block drain to collect water from subsurface water level. So it laid below the water table to collect groundwater. It can be also used to collect water from the subsurface of rivers.

Infiltration gallery diagram

Infiltration gallery equation

the equation for a yield of infiltration gallery:

\[q=k\left( \frac{{{H}^{2}}-{{h}^{2}}}{L} \right)\]

Where,

q = yield of infiltration gallery,

k = coefficient of permeability,

H = depth of permeable stratum above the bottom of infiltration gallery,

h = height of water surface level inside the infiltration gallery,

L = distance from which seepage or infiltration takes place.

What is infiltration well?

Infiltration wells are also called interception well. It is constructed as surface water will run off in it through piping. The main purpose of an infiltration well is to infiltrate surface runoff into the ground and improve the quantity of groundwater. It does not have a direct outlet into the ground. It will infiltrate through soil and seepage from porous material which is used to make infiltration well.

It is normally constructed at the lowest point of depression. Generally, precipitation infiltrates through vegetation that is permeable, and the remaining will runoff on the surface, due to more industrialization and urbanization more surface is covered and less infiltration is done. So this technique balances the hydrological cycle and helps to recharge underground aquifers. Sometimes gravels, filtering soil, etc are used in well to improve quality and remove unwanted particles and impurities.

Also Read: What is Aquifuge, Aquifer, Aquiclude and Aquitard in Geological Formations

Uses of infiltration gallery

uses of infiltration gallery are:

• Infiltration gallery is mainly used for the water supply system.
• It is used to take out the subsurface water in case of surface water is not available and water supply is needed to fulfill the requirement.
• Infiltration gallery is used to collect water from aquifers below the water table which is an easily available water resource through this by collecting them to the well for irrigation and other uses.
• Infiltration gallery is used when direct surface water is contaminated or not suitable to use.
• It is used where surface runoff is more and specially used in the dried area where surface water resources are not available to the water supply system.

Process of infiltration gallery

The infiltration gallery is constructed with a combination of other water supply systems to fulfill the increasing water demand. The infiltration gallery alone can not reach the whole supply-demand.

An Infiltration gallery works best when it has permeable soil around it-, because from sufficient permeable soil infiltration gallery can easily infiltrate the water. Gravel is the best example of preamble soil material that has big size components so water can easily infiltrate. It also removes big unwanted particles to come in way of infiltration and clog the perforated holes.

Generally, more than one infiltration gallery is constructed that is connected to a center like a hand-dug well or else, so this center is called a collecting well.

These galleries are constructed in such a way that they will not get contaminated. So a safe standard distance of 30 m is maintained on all the sides from a contaminated area or something which can contaminate the water. The safe distance may vary according to site and situation.

The Infiltration gallery is situated at a distance where unfiltered surface water can not be entered.

So through infiltration galleries water is collected at collecting well and from there it was taken out through pumping system, or with other water supply system to match the required water supply-demand.

Also Read: All You Need to Know about Rainwater Harvesting System

Infiltration gallery construction

Construction of the infiltration gallery is recommended to be done at end of the dry season. Also, the location of the gallery needs to be selected as one meter below the water table throughout the dry season.

We here discuss the basic steps of construction of an infiltration gallery, which include excavation, base preparation, pipe or drain block installation, and clay layer preparation.

Excavation

As we know that infiltration gallery helps to take out the subsurface source of water. So perforated pipes are inserted for that, and for that, a trench is excavated and it is supported by formwork and supports during this excavation process so that trench will not collapse.

Base preparation

After the excavation of the trench base need to be created to properly support pipes or drain block and for permeable surrounding. Here a layer of gravel is laid on the base of the trench and leveled as needed.

Pipe or drain block installation

The main part of the construction this, a perforated pipe or drain block through which water will infiltrate and collected. A pipe or drain block is installed over the prepared base of gravel. And after that more gravel is added on all sides of the pipe or block properly. It will create a permeable layer around the pipe or block drain.

Clay layer preparation

Over the gravel layer, fine size clay is deposited to cover it. It will prevent surface water from entering.

Infiltration gallery formula

The formula for infiltration gallery is as,

\[\begin{align}
& S=\frac{Qx}{2T\ D}…..(1) \\
& {{u}^{2}}=\frac{{{x}^{2}}S}{4T\ t}…..(2) \\
\end{align}\]

Where,

\(x\)= distance from drain to the point of observation

\(Q\)= yield of infiltration gallery,

\(t\) = time period,

D(u) & u²= drain function, it is defined from the table and the chart below as per the given data.

Difference between infiltration gallery and infiltration well

Infiltration gallery	Infiltration well
The Infiltration gallery is made for the purpose to use subsurface water.	An Infiltration well is made for the purpose to infiltrate water in-ground and conserving unconfined groundwater quantity.
Pipe or block drain installed with the permeable layer in surrounding to collect water.	A well is constructed with a permeable wall and filtering material through which water can infiltrate without contamination.
It is used when surface water is not available in dry seasons.	It is used for recharging groundwater(subsurface water).
One or more galleries are constructed and together connected to a collecting well, all this covers more area.	Only a well is constructed so its coverage is less than a pond.
Groundwater or subsurface water is extracted.	Groundwater will recharge and quality is improved.