Landscape Newsletter Issue 10
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Water and Allan Block Retaining Walls Go Hand In Hand
"British Columbia might be the greenest place on the planet", says Rob Hughes, Allan Block sales rep. for CCI Industries. "And it could also be one of the wettest. We had 45 consecutive rain days here recently, and more is on the way".

With that kind of weather, water management is always a key to good landscaping. "As I explain in the classes I teach, the best time to do an estimate is when it rains, because then the contractor will see the existing drainage patterns at the site. Understanding where the surface water goes and how the contractor can eliminate potential problems is half the battle when building Allan Block Walls in British Columbia", said Hughes.

AB Stair Application
AB Collection Stairways

 The contractors for this project followed the Plan, Design, Build process. At their first meeting with the clients they visualized what the homeowners, the Koes, described as their perfect landscape. "We wanted to develop the entire backyard into a fully landscaped space", said Mrs Koe. Using their notes from the site visit and their many years of experience, the contractors prepared a detailed site plan. Water management details were incorporated into the plans.

The challenge at the site was water management. The Koes wanted a large paved area immediately off the back of the house. The run-off from the roof would drop onto the new paved patio. All this water had to go somewhere and could not be diverted off their property.

The yard is surrounded by other properties, and draining the run-off into their yards would create problems too. The answer was a gravel path that doubled as a drain field. The paved surfaces were gently sloped towards the walkways. Stepping stones were set into the gravel bed for walking. And low-profile AB Junior walls frame the walkways to help hold the water in the drain field, and to transition the slopes of the yard. This allows water runoff to flow to the lowest point in the landscape, where a catch basin was installed with connecting drains to route the water away.

The overall effect is a graceful, terraced backyard with built-in water management. Good planning and a thoughtful design have the homeowners delighted. "We haven't had any water or drainage problems since the project was completed, and we love the overall design", said Mrs. Koe. The design of this project really flows and because of some good planning, run-off from the heavy rains of the Pacific Northwest does too.

Small garden retaining wall

Water In The Landscape
Water has become a signature feature in today's landscaping. Ponds, waterfalls, and running streams are among the most popular items on many homeowners wish lists.

Allan Block provides a great building block for creating and integrating water features. 		Curved retaining wall with the AB Europa Collection

Retaining wall with water fall
Retaining wall planter with pond
  • Waterfalls cascade through AB walls to create dramatic effects.
  • Natural stone and AB work together to simulate a babbling brook.
  • Courtyard makes a perfect form for above or below ground ponds.

Build a pond with the AB Courtyard Collection



Enhance your flower garden with a beautiful pond using the AB Courtyard Collection. With this flexible system you can build a pond without any special tools or materials and without splitting blocks.

Build a Pond Lay out the location where the pond will be. Mark the position of the liner that is being used. We recommend a 6 ft diameter plastic liner (1.8 m).

Excavate the area outside the liner 3 in. deep (75 mm) and 8 in. (200 mm) wide. Fill in the trench with wall rock, level and compact.

Install the first 2 courses of AB York block at the same time to ensure proper alignment. Check the blocks for level and proper circumference of the circle. Stack additional courses to the desired height.

Place the liner inside the ring of blocks. Position the Wall Caps and glue them down with concrete adhesive. This will lock the blocks together and prevent unwanted disassembly.

Add decorative rock and accessories.
For more detailed instructions see How-to sheet #280.

AB Above Ground Pond

AB Below Ground Pond

Construction Tips for Proper Water Management

Good landscaping doesn’t create water problems - IT SOLVES THEM.

Use the right Wall Rock

To promote in-wall drainage, you should always use crushed stone or gravel that is fairly free of fine grained material (less than 10%). The Wall Rock, placed in and around the block on every course, will allow incidental water to filter down and work its way out from behind the wall.

Wall Rock makes compaction easy around the blocks and locks them tight together. It also acts like a filter, keeping the fine-grained soil from bleeding through the face of the wall. 		Example of wall rock

When do I need in-wall drains?
Follow these rules of thumb:

  • All walls taller than 4 ft (1.2 m)
  • Sites with poorly drained clay soils
  • Alongside paved areas
  • With slopes above the wall
  • On multi-tiered and terraced walls
  • All commercial and municipal projects
Site Plan

Plan


  • Site Grading - Prior to constructing the wall, evaluate the entire site to ensure proper grading. Direct water away from the walls to help manage surface drainage.

  • Concentrated Water Sources - Identify concentrated water sources and take them into account during the design of the wall. Examples include:
    • Slopes above the wall
    • Driveways that slope towards the wall
    • Roof downspouts
    • Lawn, landscape irrigation systems and outdoor faucets

  • Ground Water - Identify the ground water elevation, which is defined as water that occurs within the soil. Ground water movement must be prevented from coming in contact with the wall structure. If ground water is encountered, contact your local engineering professional to ensure that water has been accounted for in the design.

Design


Water can be managed in two ways; surface run-off and in-wall drainage.

Surface Run-Off is handled by site grading and incorporating berms and drainage ditches (swales) to handle the water before it gets close to the wall.

In-Wall Drainage is meant for incidental water only and includes the following:

  • Wall Rock - Use wall rock in the block cores and behind the wall to ensure in-wall drainage. The wall rock should extend 12 in. (300 mm) behind the wall.
  • Toe Drains - Toe drains are used to prevent water from being trapped behind the wall and building up hydrostatic pressure. For this reason they must be positioned at the lowest point possible to allow the water to flow to daylight.


 Drainage Swale Section

In-Wall Drainage

FACT: 90% Of Wall Failures Are Caused By Improper Water Management
Irrigation Systems - When irrigation systems are used they should be designed and installed to perform irrigation in a controlled and reasonable manner.

  • The system should incorporate planning and equipment to prevent over irrigation that could saturate the soils behind the retaining wall.
  • Allan Block recommends that all sprinkler heads and piping be installed 10 ft (3 m) behind the wall to prevent problems associated with broken lines or faulty sprinkler heads.
  • Even with relatively flat grade above the wall, berms and swales should be utilized in the event of over irrigation. This will prevent surface water from ponding above the wall.
  • An outdoor faucet can also cause problems if it leaks or is accidentally left on, creating a water build-up behind or above the wall.
 Sprinkler

Build


  • Always build on solid ground. Check the base trench before you place your wall rock and install your first course of block. Any soft or saturated soils must be removed and replaced with additional wall rock.
  • During wall installation temporary grading must be in place to ensure water will not be draining towards the construction area. Constructing and maintaining temporary ditches and berms daily will prevent the on-site soils from becoming saturated.
  • Use a sheet of poly or tarps to cover stockpiled backfill to prevent saturation.


Vent your Toe Drain to Daylight
Vent to a lower grade
The preferred method places the toe drain as low as possible in the trench. From there, you will need to find a lower grade to vent the drain line to.


Vent thru the block face
If the base elevation of the wall is already at the lowest point, you can move the toe drain up above the grade at the base of the wall. The material below the toe drain will need to be a low-permeable granular material to direct any water towards the vent. Attach tee fittings at 30 to 50 ft (9 to 15 m) intervals and direct the drains out through the retaining wall face. 		Retaining Walls Drainage Options