Proactive flood prevention measures have become essential for urban centres due to the rapid worldwide growth of infrastructure. Stormwater conveyance systems prevent erosion and scouring of land and infrastructure from fast-moving water. They also provide an initial filter for runoff debris before water moves downstream to other water channels. These systems collect stormwater from different sources and flow into other stormwater management systems (bioretention ponds and rain gardens) or directly into streams and reservoirs.

Stream Banks, Storm Drains, Street Gutter and Piping Systems, Inlets to Catch Basins Solutions

When thinking of "Stormwater Management Systems", storm drain canals - with street gutters as the main source of water - typically come to mind. Storm drains are large, permanent, constructed swales or canals with many contributing water sources. Runoff is intentionally directed toward these drainage and conveyance channels, which are built to withstand large volume storm surges. After the runoff's arrival at the storm drain or inlet's graded stream banks and streambed, it commonly flows downstream to a safer aquatic destination.

During severe storms, stormwater conveyance systems receive, contain and funnel water away from pipes and street gutters. The banks of these waterways are frequently embedded with low-absorption, weatherproof retaining walls on each side. The reason for that is when dealing with massive, intermittent quantities of rapid-moving water, retaining walls provide much-needed strength and durability. These critical drainage channels are frequently lined with riprap (large stone) to slow runoff and filter out sediments and debris.

Design Considerations for Conveyance Channel Retaining Walls

High Water Mark - The average maximum height that a body of water is expected to reach during a period of flooding.
Low Water Mark - The average low water elevation that stays consistent and is typical throughout the year.
Flow Rate - Peak flow rates should be determined to ensure adequate wall stability and height, as well as channel width for the conveyance channel.
Weir - A weir may be designed for discharge into or from the conveyance channel, specifically where peak flow rates are excessive.
Rip Rap - Rip rap should be used along the toe of the walls to slow water flow, protect the wall facing, and to prevent scour. Additional scour analysis and rip rap sizing calculations should be completed separate of the wall design analysis.
Drain Gravel - Drain gravel is used in the retained infill zone or reinforced zone when using geogrids. A well draining coarse gravel (often referred to as AASHTO #57 stone) with little to no fines should be used 1 ft (304mm) above the high water mark. This material can be used inside the hollow cores of the retaining wall units and can also be used to backfill behind the wall.
Perforated Drainpipe - A perforated drainpipe, also known as a weeping tile, should be used for proper drainage behind the wall face. These pipes typically have a 4" (101mm) diameter and may be sock wrapped. All drainpipes may outlet (daylight) through the wall at a minimum of every 30 ft (B.0 m) on center. The elevation of the first drainpipe should be above the high water mark by a minimum of 6" (152mm). A second drainpipe should be added above the low water mark. Additional back drain(s) may be added where necessary at the discretion of the Design Engineer.
Soils - A full soils analysis report should be prepared using boring logs to determine the suitability of the site soils. A Geotechnical Engineer should be consulted to perform the analysis and report findings.
Filter Separation Fabric - Filter fabrics, also known as geotextile, should be used to separate the fine soils from the drainage layers. They may also be used between the back.' material and retained material along the excavation cut. Wrapping the levelling pad will assist with scour and erosion of the base levelling pad.
TOW - Top of retaining wall elevation. Typically, the top of the cap; shown in plan views a. wall profiles and are essential for construction.
BOW - Bottom of retaining wall elevation. The base of the wall where the ground level meets the retaining wall; shown in plan views and wall profiles and are essential for construction.

Why Use Stormwater Conveyance Systems?

The importance of conveyance systems is rooted in conservation. While household rainfall conveyance systems are an excellent solution for gardens and soil via infiltration, stormwater conveyance systems and drainage channels help control larger volumes of water which have the potential to wipe out infrastructure.

Drainage systems are imperative to massive urban areas, primarily functioning as erosion control structures and flood protection. Rightfully, people often associate stormwater drainage channels with images of the famous Los Angeles River, which is a perfect example. This waterway helps mitigate flooding and erosion by conveying water for miles until it reaches its outlet to receiving waters; in this case, that is the Pacific Ocean.

But not all drainage channels have to be iconic, world-renowned systems, of course. MagnumStone retaining walls perform the same water conveyance functions for projects of any size or complexity. Our blocks serve as excellent, secure and long-lasting reinforced stream banks for critical drainage systems. Additionally, the blocks are perfectly suited to create weirs along these waterways which control water flows.

Features & Attributes of Stormwater Conveyance, Drainage Channels, Stream Banks

Stormwater Conveyance and drainage channels tend to be noticeable within communities and urban areas. These open-surfaced, engineered canals and swales are designed to receive, control and guide water downstream. Concentrated waterways of this kind are capable of handling large, sporadic volumes of water and are highly effective during storm surges. Structures for these applications can be fenced off at the top of the drainageway to prevent objects or people from entering the water channel.

Surface runoff comes mostly via street gutters and underground piping systems, where water is lead to these centralized drainage channels. It is always recommended that the drainage pipes in the retaining wall and clean gravel backfill remain a minimum of 12 inches (300 mm) above the high water mark for any water application, including stormwater drainage channels. This area is wrapped in a filter fabric to prevent fines from migrating into the clean drainage areas.

Stormwater channels are typically formed in canal shapes or with steep streambanks, which are lined with retaining wall blocks to prevent erosion and scouring. Since these retaining walls face tough water application conditions, they may also be further reinforced by geogrid. Another form of conveyance system are step pools, elevated water pools engineered to fill from the top and overflow into the next pool below, thus slowing water speeds and filtering pollutants.

The streambeds of these waterways have riprap or vegetative bases which control water flows. These features act as the first filtration or settling area for sediment sand debris from the infrastructure runoff. Stormwater drainage channels can help treat water and remove contaminants. Cleaner water then flows into larger receiving waters such as rivers, streams or lakes.

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Gravity Solution

Geogrid Solution

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MagnumStone's Advantages

  • An eco-friendly product, hollow core design uses 40% less concrete than solid concrete systems
  • Hollow core units are filled with clear crush gravel and perforated drainpipes for an exceptional built-in free flow drainage system and permeability that prevents sediment buildup
  • The gravel-filled MagnumStone blocks provide weighted strength for gravity walls, or with the help of geogrid for reinforced walls, along with clear crush gravel backfill for advanced drainage
  • Natural facing rejuvenates and enhances aesthetics of stormwater drainage channels, with added benefits of superior strength, durability and looks than gabion wall structures
  • MagnumStone’s precast wet-cast concrete retaining wall blocks are low-absorption
  • Perform great in grueling weather for any water applications with runoff moving through and away from the retaining wall
  • MagnumStone's lightweight blocks and gravity extenders are quick and easy to install, excellent for tight excavation spaces, making better use of land and properties or tight urban areas
  • Protects properties, structures and utilities from erosion, can be further strengthened by geogrid
  • Has the strength to withstand powerful water surges and scouring
  • Promotes effective soil retention and concentrated soil
  • Approved by governments and Departments of Transportation

Design Resources for Stormwater Conveyance Retaining Walls

The MagnumStone system has a powerful and easy to use design engineering software that is free to all users. The software not only checks for wall overturning, bearing capacity, and sliding, it also provides global stability, seismic loading, in water conditions and many more analysis that are critical to a comprehensive final design.



Download our completely free and fully featured retaining wall design software today and develop projects with precision. Click on the link below to discover the full list of features and download it today!

Design Software


All related documents for this design option are listed here, or to view our entire downloads catalog click here

Case Study – MagnumStone Retaining Walls Stream Bank Protection for Stormwater Conveyance

Stormwater Conveyance Channel Streambank – Geogrid CAD Details

Stormwater Conveyance Channel Streambank – Gravity CAD Details

Interlock/Drainage Detail

Railing In Core Design

Swale Detail

Inside Curve Detail

Outside Curve Detail

Inside Corner Detail

Outside Corner Detail

Concrete Culvert 18 Inch

Concrete Culvert 30 Inch

Case Studies

MagnumStone’s Superior Stream Bank Protection

New Columbia, PA

February 4, 2016

MagnumStone Takes Off at Major Canadian Airport

Edmonton, Alberta, Canada

April 5, 2021

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