Drain Away Excess Water with a Curtain Drain Trench

What is a Curtain Drain?

A curtain drain is a type of drainage system that consists of a trench filled with gravel and perforated pipes used to divert water away from a structure or area prone to pooling or excessive moisture. Curtain drains are also sometimes referred to as French drains. The purpose of a curtain drain is to capture and remove excess surface runoff and groundwater to prevent flooding, erosion, mold growth and damage to building foundations.

Curtain drains get their name from the "curtain" effect created as water is absorbed from all sides along the length of the trench. This comprehensive drainage protects the site from subsurface water damage.

Key Components of a Curtain Drain

The key components of a curtain drain system include:

• Gravel - The trench is filled with gravel which provides voids for water flow and filtering.
• Perforated pipes - Perforated PVC or corrugated pipes at the bottom of the trench collect and transport water away from the site.
• Filter fabric - Lines the trench to prevent soil and sediment from clogging the gravel and pipes.
• Outlet - Connects the pipes to a downspout, storm drain or other discharge point.

Why Install a Curtain Drain?

There are several important reasons to have a curtain drain installed on your property:

Prevent Water Damage

Excess moisture around a home's foundation can cause flooding, mold growth, mildew and water damage. A curtain drain will capture and divert water away from the basement and crawlspace areas before it can seep in and cause harm.

Manage Excess Water

Curtain drains are effective for draining away standing water from yard areas prone to ponding. They can also protect septic drain fields by preventing groundwater from saturating the soil treatment area. Proper drainage prevents erosion and sinkhole formation.

Improve Drainage

Curtain drains can provide an outlet for roof and gutter downspouts, channeling large volumes of water away from the structure. They also help relieve hydrostatic pressure near foundation walls that can lead to cracks and water entry. By improving drainage, curtain drains enhance soil stability.

How Does a Curtain Drain Work?

A curtain drain leverages gravity flow, requiring proper slope and positioning for optimal performance. Here is an overview of the water flow process:

Water Flow Process

Surface and groundwater enter the open gravel trench from all sides. The water fills the void spaces in the gravel and flows into the perforated collection pipes at the base of the trench. These pipes are sloped to channel the water away from the site to a storm sewer grate or lower elevation discharge point on the property.

Gravel and Fabric Filters

The gravel contains small, uniformly sized rocks that provide maximum void space for water flow while filtering out sediment. The fabric barrier lining the trench prevents soil particles and debris from the surrounding earth from clogging the gravel. This keeps the system free-flowing.

Proper Slope Essential

An adequate slope is necessary for the curtain drain pipes to leverage gravity drainage. The standard recommended pitch is 1/4 inch vertical drop per horizontal foot of pipe. With proper slope, the water flows freely through the pipes to the outlet without pooling in the trench.

Curtain Drain Design Considerations

Several factors go into planning and designing an effective curtain drain for your specific property:

Positioning Factors

The trench should be placed:

• Below the frost line to prevent freezing
• At least 10 feet from foundation walls
• Downhill from the structure requiring drainage

Layout Options

The trench can be configured in a straight line, L-shape, or other layout conforming to site topography. Following the natural contours and low areas ensures water flows into the trench.

Material Selection

Pipe diameter, perforation type, gravel gradation, and fabric density should be selected based on site conditions and drainage requirements.

Curtain Drain Installation Process

Proper installation is key to an effective curtain drain system. Here is an overview of the main steps:

Planning the Project

Thorough planning involves evaluating the site, taking measurements to determine trench placement and sizing, and designing a layout to fit your specific needs.

Excavation

The trench is dug with a slight slope leading to the outlet point. Excavated soil is mounded temporarily alongside.

Prepare Trench

The trench bottom and sides are lined with filter fabric. A layer of gravel is added to support the perforated pipes.

Install Pipes and Backfill

Perforated collection pipes are laid with proper slope to drainage outlets. The trench is then backfilled with gravel over the pipes.

Surface Restoration

Once installed, the trench is buried by grading the soil back over the gravel and seeding to restore the surface.

Professional installation is recommended to ensure optimal placement and performance. But with proper planning and preparation, installing your own curtain drain is an achievable do-it-yourself project.

Additional Curtain Drain Benefits

Beyond diverting water from structures, curtain drains provide other important benefits:

Reduce Erosion and Landslides

By diverting surface runoff and groundwater flows, curtain drains help minimize soil erosion on slopes and prevent dangerous mudslides or landslides.

Promote Healthy Plants

In areas with poor drainage, curtain drains can prevent soil from becoming waterlogged so plants and lawns remain healthy.

Enhance Aesthetics

By diverting and dispersing excess water, curtain drains create evenly graded, attractive landscapes devoid of ponds and soggy patches.

Types of Curtain Drains

There are several configuration options when installing curtain drains:

Surface Curtain Drains

Installed along the surface with gravel fills and grated covers. Excellent for slopes and areas with fast drainage needs.

Subsurface Curtain Drains

The typical below-ground trench configuration. Best for foundational drainage and stability.

Porous Curtain Drains

Uses very porous fill material to allow water to be slowly absorbed into the soil.

Curtain Drains and Stormwater Management

Curtain drains are an important tool for comprehensive stormwater management:

Reduce Urban Flooding

By diverting runoff from saturated soil, curtain drains can prevent overloaded storm drains during heavy rains.

Slow and Disperse Water Flow

Curtain drains help reduce flash flood risks by slowing and spreading out water flows entering storm sewers.

Climate Change Resilience

With climate change bringing heavier rains, curtain drains are an adaptation strategy:

Prevent Ash and Debris Runoff

In fire-prone regions, curtain drains can capture contaminated runoff during post-fire storms.

Reduce Storm System Strain

By diverting water into the ground, curtain drains help take pressure off municipal stormwater infrastructure.

Sustainable Water Management

Curtain drains promote sustainable practices:

Enhance Green Infrastructure

Curtain drains can be integrated with rain gardens, bioswales and other green systems to reduce stormwater.