With discharges that range from a trickle to high velocity deep flows, the open channel drainage and storm water conveyance systems of Loves Park Creek, storm water flooding was only one of several challenges facing City of Loves Park community. The channel meanders through industrial and residential areas which puts residential property and municipal playgrounds at risk with the highly erosive forces. The flows typically carry high sediment loads depositing them along numerous areas throughout the channel. These sediment deposits created a multitude of hydraulic problems and diminished the channel's capability to rapidly convey storm water thus causing severe flooding. Sediment deposits were normally dealt with by periodically excavating the channel; however, without a hard surface floor to run equipment on, excavation of sediments was often difficult and sometimes infeasible.

In the past, some portions of Loves Park Creek were hard surfaced by use of cast in place concrete. Although the concrete proved to be extremely effective in providing a load-bearing surface to support sediment clean out equipment (skidsters and small end loaders), homeowners were not pleased with the aesthetics. As the concrete aged and freeze-thaw cycle damage became evident, cracking and heaved slabs became more common. Property owners wanted a solution that would not turn their community into a concrete jungle or dumping ground for rubble and rock. The City of Love’s Park and residents sought a treatment that provides:

• Erosion control.

• Natural aesthetic beauty.

• Reduction of sediment deposits.

• Resistance to damage from freeze-thaw heaving.

The U.S. Army Corps of Engineers–Rock Island District, were charged with the task and proposed the optimum solution - Articulated Concrete Blocks (ACBs) that could be vegetated. Stringent specifications were written and the HydroPave Conlock II system was selected. The Conlock II system provides high hydraulic permissible shear resistance and each individual grid exhibits two interlocking ears and two interlocking sockets. This design allows for positive interlock of all grids within the matrix. This interlock slides with ground movement and provides for omnidirectional terrain surface contouring and a continuous uninterrupted interlocked field matrix. Unlike other ACB systems, the Conlock II system exhibits a continuous interlock and co-planar surfaces when encountering most all grade contours such as domes, depressions or channel constrictions.

The high vegetative open voids allow for a more aesthetically pleasing channel. The natural beauty of the channel blends more comfortably with the community while maintaining balance in the incomparable eco-system. This is becoming increasingly more important with the increase in governing agencies development of guidelines and policies implemented to change the impact to the environment.

“Stormwater Phase II final rule of the EPS’s National Pollutant Discharge Elimination System (NPDES) requires urbanized areas to reduce impervious surfaces, mitigate common pollutants, and reduce overall stormwater discharge,” Richard Bodie, Pavestone Company, Dallas explains. “HydroPave Erosion Control systems are open cellular blocks have proven to permeate precipitation, as well as providing vegetative cover for the potential to filter contaminants. These properties make the selection of the HydroPave system a candidate for Best Management Practices along with the measurable goals for reducing quantity and the quality of stormwater discharge.”

With stringent specifications written, the bid process proved the HydroPave Conlock II system to be the most cost effective as well as meeting the project objectives. Over 274,000 square feet of Conlock II 6VM-30 block were installed on two separate phases of the project. Contractor crews experienced installation rates up to 75 square feet per man-hour. Unit to unit articulation results in a minimum maintenance and an extended product service life. Competitively, the Conlock II system saved thousands of dollars over other conventional systems.

The articulated concrete blocks used in Loves Park Creek provided high hydraulic permissible shear resistance. The blocks have interlocking features allowing the grid to remain in place. Open cells of the blocks provide an area for vegetation to survive.

Guidelines for the selection and design of the appropriate ACB product are provided by the Federal Highway Administration (FHWA) publication–Hydraulic Engineering Circular 23. The publication presents a procedure to develop hydraulic design criteria given the performance data for an ACB such as the Conlock I & II products’ hydraulic stability testing performed by the St. Anthony Falls Hydraulic Laboratory. Both documents are available in the HydroPave Technical Binder.

Structurally sound engineering combined with aesthetically pleasing features and competitively priced, ACBs are effective solutions to creating eco-friendly land development. Success of the bio-stabilization effort is centered on practicing common sense approaches to block selection, site geology, plant species and hydrology.

Alva Logsdon is a frequent contributor to Landscape Contractor Magazine. Richard Bodie serves on the NCMA Technical Committee and Landscape Products Committee; he may be contacted at (817/481.5802). HydroPave, a division of Pavestone Co., has an experienced technical staff preliminary design engineering assistance and site specific CAD details installation drawings for erosion control. HydroPave has over 20 years of field experience in designing and installing Conlock ACB block systems worldwide. Technical Binders, CAD files and Design Programs are available on request. For more information on erosion control and ACBs, go to: www.pavestone.com or www.hydropave.com.