Developer Hani Shafai believes that if a historically strong rainstorm should ever settle above east-central Rapid City, 200 homes could be washed away. City officials say they’re working to ensure that doesn’t happen.
At the Rapid City Council meeting on Monday night, council members approved an agreement with FMG Engineering for the second phase of a study investigating the existing state of two drainage basins. The study's second phase, at a cost of $146,000, will focus on the Perrine Drainage Basin and the adjacent Unnamed Tributary Drainage Basin, together encompassing an approximately 3,000-acre swath of rolling prairie and residential/commercial development south of Interstate 90, east of East North Street and west of Elk Vale Road with state Highway 44 slicing through its center.
Two of Shafai’s largest developments — Johnson Ranch Subdivision and Orchard Meadows Subdivision — rest in the basins.
At Monday’s meeting, Shafai raised several concerns about the area’s drainage, its impact on his property, and the potential that any improvements resulting from the study may impact or alter his property, its drainage and its value. He also expressed the belief that should any additional drainage improvements be found necessary on his property, he should not be responsible for the cost.
According to an analysis by KTM Design Solutions — a Rapid City-based engineering and construction administration firm — the basins violate the city’s drainage criteria by discharging outside their boundaries. Further, both drainage basins' runoff converge at a point along Highway 44 between South Valley Drive and Elk Vale Road to a peak flow of 1,056 cubic feet per second in the event of a 100-year flood, which has a 1 percent chance of occurring each year. That peak flow represents almost half the estimated flow of Rapid Creek in a 100-year flood event.
Public Works Director Dale Tech said those issues are the reason the city has commissioned FMG for the study. Phase 1 was completed this summer for around $46,000.
“We believe that this is going in the correct direction,” Tech said. He noted that the potential for flooding and private-property damage was being considered and options to address the situation are “another thing that will evolve through this next phase of this plan.”
“We’ll listen to any concerned citizen out there,” Tech said.
The city expects FMG’s final report, with drainage improvement recommendations, to be completed by Oct. 30, 2019. In the past, Tech has said that a previous city study found it would cost $140 million to fully develop all the city’s drainage basins so they were in line with current development in the event of a 100-year flood.
In other action, the council:
• Authorized the city to enter into an agreement with the city of Summerset to contract out a feasibility study looking into possibility of connecting Summerset’s sanitary sewer lines to Rapid City’s existing system. Significant capital improvements are needed soon at the Summerset wastewater-treatment plant and both cities see a potential benefit if Rapid City provided collection and treatment at one facility, according to city documents. The cities will split the cost of the study 50/50 — estimated at $60,000 — which will evaluate potential locations for the sewer connections, examine the capacity of Rapid City’s collection system, and estimate the cost of the necessary infrastructure improvements and cost of service.