Fargo, ND – Crofton Coves Development
Owner: City of Fargo
Completed: 2014
Total Cost of Project; $4,196,644.11
Challenge:
Moore Engineering provided L2H Development with preliminary survey for a residential development site in south Fargo in the spring of 2013. Preliminary survey included an 81-acre site topographic survey, preliminary plat and final plat preparation. On July 16, 2013 a final plat was recorded with Cass County and engineering design work was started on the infrastructure improvements.
Solution:
Infrastructure improvement plans for sanitary sewer, water main, storm sewer, paving, street lights & incidentals were design during the summer of 2013 and bid in the fall of 2013. The design included a 9.3 acre wet retention pond and a 2.4 acre dry detention pond.
The larger pond was created to fulfil a number of functions. With a permanent water pool 8 feet deep and covering 3.7 acres, it was conceived as an integral part of the development’s aesthetic character. The wet pond provides the centerpiece visual attraction in the development, and included 3 lighted fountains, a walking path, and special grasses planted to enhance the visual appeal.
Since the wet pond is intended to be an attraction, all side slopes above the normal water line were kept at 8:1, with an 8 foot wide bench approximately mid-way down to the normal water level. The bench provides a flat area for a walking path and for maintenance access. A safety feature is provided in the form of a 30 foot wide bench just below the normal water level, allowing easy egress from the pond for anyone entering it either accidentally or for maintenance. Subsurface side slopes are 10:1 based upon a geotechnical long term stability analysis of the soils.
The wet pond also serves as the major storm water detention facility. The large volume also provides water quality advantages for all rain events by acting as a sedimentation basin. The wet pond, the dry pond and the storm sewer system are designed to act together to provide the entire development with flood protection for a 100 year rainfall event. The system as a whole was carefully modelled to verify the interconnecting storm sewer pipes are sized to make maximum use of the storage volumes in the ponds, including backwater effects from the storm sewer pipes the pond discharges to. Upstream and downstream effects were checked, and the discharge pipe sizes were optimized to prevent adverse effects.
The final feature of both the wet pond and the dry pond is to provide a ready source of fill material for the rest of the development. The pond size and depth were selected in part to balance the total earthwork on site, and provide enough additional material to balance a future adjacent development. Excavation from the ponds were used to elevate the residential lots out of the flood plain and provide flood proof elevations for new homes.
Construction began in the fall of 2013 and continued in the spring/summer of 2014 with substantially completion in the fall of 2014.
Outcome:
Moore provided construction engineering, construction administration, construction inspection and survey staking services for underground utilities and paving for the City of Fargo. Services included 5,000 linear feet of sanitary sewer main staking, 5,700 linear feet of water main staking, 87 sanitary and water service staking, 6,100 linear feet of storm sewer staking, 10,300 linear feet of concrete curb and gutter staking, 19,400 square yards of subgrade grading and asphalt pavement staking, 2,600 square yards of concrete sidewalk and multi-use path staking, 34 street light pole staking and 167,200 cubic yards pond and lot grading staking. Services for LOMR-F certification were provided for 141 home sites within the development. Final lot grading was verified by topographic survey on the 141 home sites to meet the requirements of the LOMR-F certification.
