Final phase of Spearfish Creek floodplain remapping project approved

September 7, 2018

SPEARFISH — The proposal for engineering services for the final phase of the Spearfish Creek FEMA (Federal Emergency Management Agency) re-mapping project, which involves the analysis and mapping of the creek and the floodplain impacts, was approved Monday by the Spearfish City Council. It does not include any mitigation options to prevent breakout flows, as studied during a previous phase of the project, and based on rough estimates, the new map could result in 551 parcels in the city and county included in the regulatory floodplain, versus 347 parcels currently included. However, final numbers won’t be known until FEMA considers and approves an updated map.

This phase follows previous segments of projects undertaken with the goal of updating the floodplain maps related to Spearfish Creek. In February 2017, the council approved a proposal from AE2S (Advanced Engineering and Environmental Services) for the floodplain remapping project, at a cost not to exceed $109,300. Lawrence County provided $22,000 of funding for the project, which includes areas within both the city and county, about five miles of Spearfish Creek from just north of Interstate 90 to Spearfish Canyon.

In November 2017, the council chose to take an additional step prior to submitting the drafted floodplain maps to FEMA to identify potential mitigation projects that could reduce areas of floodplain within the study area due to the changes between the current and preliminary floodplain limits, which would remove or add various parcels in the study area to the 100-year floodplain boundaries. Any mitigation efforts to address breakout flows would need to be factored in to the study prior to submitting the working map to FEMA, to accurately reflect how the water would move in a flood event. The council chose to participate in the Spearfish Creek Flood Protection Improvements Planning Project, for a total fee of $40,350, to be split between the city and county. The areas identified for further study for flood protection improvements included: Hillsview Road, Evans Lane, Evans-Tonn Ditch, areas south and north of U.S. Highway 14 near Exit 10, and South Canyon Street, and each task proposed was divided into a city-county cost share to reflect how the tasks would benefit each.

The council and Lawrence County Commission in April heard the results of the study, which listed more than $3 million in approximate costs for mitigation projects that, based on estimates, could reduce the regulatory floodplain in the city by a net of 105.8 acres and the county by a net of 157.3 acres.

After considering the options and costs, the city and county decided to submit the maps without completing any mitigation improvements, and Monday, the city council approved the proposal from AE2S for engineering services to complete the final phase of the Spearfish Creek FEMA re-mapping project, which includes the analysis and mapping of Spearfish Creek and the floodplain impacts on the community and concludes with the submittal of a final Letter of Map Revision (LOMR) to FEMA at a cost not to exceed $58,900.

City Engineer Kyle Mathis explained that the breakdown of costs is: Engineering, $50,700, and FEMA LOMR application fee, $8,250. Lawrence County has preliminarily included a portion of this expense in their 2029 budget, with an estimated reimbursement of $29,475.

Mathis explained that staff recommends moving forward with the floodplain study without mitigation improvement projects being completed and that funding would come from second penny. There is approximately $45,000 remaining from a previous phase of the project that would more than cover the city’s portion of the cost for this phase, he added.

Mathis said that at previous meetings, elected officials asked for comparisons of assessed values, looking at properties currently in the floodplain versus what would happen by going through and remapping the area as presented.

He provided rough estimates: As far as assessed values within the city, currently, there is about $58.4 million of assessed value within the floodplain, and with the new map, that could increase to more than $65 million.

“Now, it’s important to remember how this was evaluated,” Mathis explained at the Public Works Committee meeting Aug. 28. “Any portion of a parcel was touched was floodplain in this, it was counted. It doesn’t matter how much was in it; it was just counted. It would be pretty hard to break down everything on there, whether there’s buildings on it or not. If it touched a lot, the full assessed value was included in this number here.”

Total assessed value of properties within the floodplain in the county is currently about $9.1 million, and with the new proposed map, it could increase to about $27.3 million in valuation, primarily due to that breakout flow at Hillsview Road and Evans Lane, Mathis said.

In terms of parcels, there are currently 61 parcels in the floodplain the county; that could increase to about 232 parcels with the new map, Mathis explained. In the city, there are 286 parcels within the floodplain currently, and that could go up to 319 parcels in the new map. However, final numbers of parcels included in the regulatory floodplain would not be known until FEMA considers and approves the drafted map.

It is anticipated that the work for the final phase of the remapping project would take place in 2019, and it is estimated to take four months to submit the LOMR application to FEMA, and if approved, it would take about a year to become fully effective, Mathis said.

After hearing the information pertaining to the proposal, the council unanimously approved the request without further discussion.

Floodplain administration Tonya Vig said Wednesday that the findings of the final phase would be presented at the city and county level as the process continues, with public meetings to follow to notify property owners that may be impacted. At this time, it is unknown for certain which parcels may be included in the regulatory floodplain, but anyone with questions may contact Vig at 717-1131.

The most recent effective FEMA floodplain maps for the majority of Spearfish Creek within Spearfish were adopted by the city council in 2012, with an approximately 8,800-foot section from Hillsview Road to just north of Interstate 90 remapped in 2015 and approved in 2016 after the council approved a $49,975 proposal from AE2S in July 2015.

It was noted at a previous meeting that when the 2012 map was done, 250 homes were affected by the update.

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