Geomembrane used to line one side of rock cofferdam to drain one-half of Druid Hill Reservoir while maintaining water in the other half
120,000 square feet of XR-3 reinforced potable grade geomembrane by Seaman Corporation, 52,000 square feet of 10 oz double-sided geocomposite
Druid Hill Reservoir is a one-billion-gallon (55 acre)potable water storage reservoir that supplies the City of Baltimore and surrounding counties. Druid Reservoir was constructed between 1863 and 1871 and is one of the largest earthen dammed lakes in North America and in 1971 it was named a National Historic Civil Engineering landmark by the American Society of Civil Engineers.
To drain one-half of the reservoir, while maintaining water on the other side, Hallaton lined a 1,200 ft long rockfill berm to create a barrier system instead of driving steel sheetpiles as required in the original bid documents (see Photo One). The water facing side of the rockfill berm was lined with an impermeable geomembrane so water could not flow from the water filled side of the reservoir through the rockfill and into the other half while it was drained to construct underground storage tanks. First a geocomposite was placed on top of the rockfill to protect the reinforced geomembrane during deployment (see Photo Two). Afterwards the factory fabricated reinforced potable water grade geomembrane was installed over the geocomposite and floated out into the reservoir to cover the full length of the rockfill slope that was below water (see Photo 3).
Challenging aspects of this project include:
The rock cofferdam varied in depth for 0 to 60 feet over its length so each factory fabricated geomembrane panel varied in length and width to precisely cover the permeable cofferdam material to prevent leakage from the water to the dry side of the cofferdam
Keeping the geomembrane afloat as it was incrementally being pulled out across the water and cofferdam was accomplished using floats
Making the “turn” along the ponded side (see aerial shot in Photo One). The overall length of the cofferdam is 1,200 feet but 300 feet was along the southern side of the reservoir while 900 ft was along the fairly straight cofferdam. The geomembrane for the 300 foot long section was factory fabricated and then thermally welded in the field to the end of the 900 foot main section that was previously pulled into place
Sinking of the installed liner system needed to be controlled from the stone cofferdam.This required carefully timed and equally measured maneuvers on both sides to sink the liner system to the bottom of the reservoir and cofferdam. Following the successful sinking of the liner, divers were employed to ensure the geomembrane was in contact with the cofferdam to the reservoir bottom so no leakage occurred.
After stone ballast was placed on top of the completed geomembrane, dewatering started on the western side where the new underground tanks would be constructed (see Photo Four). The western side of the reservoir was completely dewatered to allow for the excavation and construction of the new underground water tanks to create a safe and protected treated water supply for Balitmore (see Photo Four).
Many lessons were learned from this project, including:
engineering smaller models and conducting many trial runs is beneficial to identify potential issues when a project involves innovative design and construction techniques;
there still may need to be some re-engineering on site to achieve best results;
good communication and collaboration between the engineer, general contractor, and geosynthetics installer is important.
HOW THE USE OF FABRICATION IMPROVED THIS PROJECT
Most of the geosynthetics were factory fabricated ahead of time, which increased the speed of the project because time was of the essence. Deploying geomembrane from the top of a cofferdam on one side, while keeping it straight, forward moving, and floating was accomplished much easier using large factory fabricated geomembrane panels (see Photos 2 and 3).
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The FGI Pond Leakage Calculator Geomembranes v. Compacted Clay Liners
Fresh water is a precious resource with demands rising daily and supply greatly fluctuating. Only two (2) percent of all water on Earth is fresh water with the other 98% being salt water. This 2% of fresh water is comprised of: 87% ice, 12% groundwater, and 1% rivers and lakes. Thus, only 13% of the available freshwater is readily accessible. Therefore, it is imperative that we capture and hold these limited water resources for agriculture, domestic use, and industry and also protect valuable groundwater from surface or subsurface contamination.
The FGI’s Pond Leakage Calculator is a Microsoft EXCEL spreadsheet based on Darcy's Law of Seepage and provides a comparison between leakage rates from a canal, pond, or reservoir constructed with compacted fine-grained soils and a geomembrane liner system. The Leakage Calculator allows the user to input the size of the containment basin (including length, width, depth, side slope angle and freeboard), the anticipated level of hydraulic conductivity of the compacted soil or geomembrane liner, and the relative cost of water in dollars per acre-foot of water.
The Calculator then calculates the volume of the basin in gallons, a comparison of leakage rates between the compacted soil and geomembrane liner systems in gallons, and the cost of the leakage based on the cost of water per acre-foot to replace it. This Calculator is designed to help consultants, engineers, architects, and end users decide how to line their canals, ponds, reservoirs, and basins to capture and/or protect valuable fresh water. The Calculator does not consider variances in construction quality and operational techniques on the long-term effectiveness of the chosen liner system. The FGI has additional research and publications to help with other aspects of successful water containment applications.
Types of Geomembranes Four (4) popular types of geomembranes are available for pond liner systems. These four (4) geomembranes in ALPHABETICAL order are: (1) EPDM, (2) reinforced polyethylene (RPE), (3) Polypropylene (PP), and (4) Polyvinyl Chloride (PVC). EPDM (Ethylene Propylene Diene Monomer) geomembranes are unreinforced and have been used for the construction of ponds of varying kinds. EPDM geomembranes are made from rubber and can be welded together with tape and primer. EPDM can be reinforced or unreinforced. RPE geomembranes have a high tensile strength and puncture resistance because they are reinforced. RPE geomembranes also can be welded with heat. PP geomembranes can be unreinforced or reinforced depending on the application. Reinforced PP geomembranes also have a high tensile strength and puncture resistance because they are reinforced. PVC geomembranes are also unreinforced and have been used successfully for decades in water canals, ponds, and reservoirs. PVC geomembranes can be welded with heat and/or solvents.
Please click below to access FGI’s Pond Leakage Calculator.
Geomembrane Attachment andPenetration Design and Installation Presented by Patrick Elliott of RavenIndustries/CLI, Brendan Simbeck, and Duff Simbeck of Simbeck and Associates Recorded February 4, 2021
Moderators: Jordan Wiechmann, Intertape Polymer Group and Jen Miller, Fabricated Geomembrane Institute
The Fabricated Geomembrane Institute at the University of Illinois has created a group titled, “Women in Geosynthetics (WIG)” in order to promote the advancement of women in the geosynthetics industry through education, networking and mentoring opportunities. Audience participation is the focus of this highly interactive discussion
The discussion will include, but is not limited to the following points of interest:
– How can we recruit MORE women into the Geosynthetic Industry?
– How can we create more opportunities in the industry for women?
– What types of educational opportunities are out there to educate women throughout the industry?