By Michael Dickey, P.E. (WI, FL, GA, NC), Presto Geosystems Director
Civil engineers are responsible for designing resilient urban infrastructure that can withstand the impact of natural disasters, extreme weather events, and changing climate patterns. To achieve this, they must pay special attention to stormwater management, which plays a crucial role in preventing flooding, controlling erosion, and maintaining water quality. A vital component of stormwater management is the construction of stormwater channels. The construction of these channels is an essential aspect of promoting the sustainability and resilience of the urban environment by helping communities withstand flooding and facilitating faster recovery from the impacts of severe weather events.
Geocells provide a cost-effective and sustainable alternative to traditional channel lining methods and provide some unique advantages. In this article, we will discuss the results of hydraulic tests conducted at Colorado State University to evaluate performance parameters for the use of GEOWEB® Geocells in stormwater channel design and construction.
Overview of Channel Lining Options Using GEOWEB® Geocells
The GEOWEB® Channel Protection System incorporates an advanced geosynthetic technology known as geocells, which can be used to facilitate a range of channel lining options for stormwater channel construction. The system integrates high-density polyethylene (HDPE) cells that are interconnected to form a flexible, three-dimensional matrix that is compatible with a variety of infill options. When used in conjunction with permeable infill options such as engineered fill or aggregate, the system allows stormwater to infiltrate the ground, recharge groundwater supplies, and reduce the risk of flooding. When used in conjunction with impermeable infill such as concrete, the system can be designed to resist very high shear forces for protection against scour and undercutting.
Hydraulic Performance Testing of the GEOWEB® Channel Protection System at CSU
To evaluate stability threshold conditions and quantify hydraulic forces and infill loss, the GEOWEB Channel Protection System was subjected to a series of hydraulic performance tests at the Hydraulics Laboratory located at the Engineering Research Center (ERC) at Colorado State University (CSU). The hydraulic performance program incorporated a variety of infill materials and geosynthetic products to simulate three different types of channel lining options as summarized in Table 1, and results for each of the major channel lining types are discussed in the sections that follow.
Vegetated Channel Protection: Hydraulic Test Results for GEOWEB Infilled with Common Soil
After the completion of multiple tests, no instability was observed for the vegetated channel tests, and the system showed no measurable soil loss. Outstanding performance was confirmed for shear stresses of up to 15.9 pounds per square foot (psf) and at average flow velocities of up to 26.5 feet per second (ft/sec). Moreover, at the conclusion of the tests, an extracted soil sample showed vegetative root penetration to a depth of 1.5 inches, with larger roots interacting with the cell wall perforations. Researchers further concluded that as future growth occurs, root interaction can be expected to increase, further improving system stability as the vegetative cover matures over time.
Aggregate Channel Lining: Hydraulic Test Results for GEOWEB Infilled with Coarse Gravel, Small Cobbles
Using data collected from 90 tests, the GEOWEB Channel Protection System with aggregate infill was evaluated on its performance as compared to rip-rap. Results showed that the required rock size for aggregate fill was at least 30 percent smaller than rip-rap as sized by Abt and Johnson (1991) and at least 50 percent smaller than sizes recommended by the Army Corps of Engineers (1994). The ability to reduce rock size highlights the potential to use GEOWEB Channel Protection System as a value engineering alternative to rip rap, especially in areas where larger rock is not locally available.
Geocell-Reinforced Hard Armor for Channels: Hydraulic Test Results for GEOWEB Infilled with Concrete
For the tests including concrete infill, it was confirmed that the established performance threshold had not been exceeded, even for the highest flows capable of being delivered to the CSU test flume. It was determined that a system comprised of GEOWEB 30V3 geocells infilled with 3000-psi concrete exhibited the capability to withstand sustained flow velocities of 35.7 ft/sec and shear stresses of 20.9 psf. Stability at severe hydraulic conditions indicates that GEOWEB with concrete can reasonably be expected to perform well in most engineering applications where shear stresses are generally much lower than the maximum level observed in the test simulations.
A Customizable Solution for Channel Protection
The GEOWEB Channel Protection System provides a cost-effective and sustainable solution for the construction of stormwater channels that can be customized to meet a wide range of hydraulic conditions to meet your project-specific needs. The GEOWEB Channel Protection System allows for permeable infill options such as vegetation or aggregate, promoting effective stormwater management and infiltration, while reducing the risk of flooding, or concrete infill, as a hard armor option to protect against scour and extreme flow events.
With its flexible design and permeable infill options, the GEOWEB System is an innovative solution that can help communities establish resilient urban infrastructure that can withstand the impact of natural disasters, extreme weather events, and changing climate patterns.