Spring Creek Tributary Floodplain Mitigation Project
Executive Order 11988 – Floodplain Management
Executive Order 11990 – Protection of Wetlands
Eight-Step Decision Making Process
Executive Order 11988 (Floodplain Management) requires Federal agencies “to avoid to the
extent possible the long- and short-term adverse impacts associated with the occupancy and
modification of the floodplain and to avoid direct or indirect support of floodplain development
wherever there is a practicable alternative.”
Executive Order (EO) 11990 (Protection of Wetlands) requires Federal agencies “to avoid
construction or management practices that would adversely affect wetlands unless that agency
finds that (1) there is no practicable alternative, and (2) the proposed action includes measures to
minimize harm to the wetlands.” The EO directs all Federal agencies to minimize the
destruction, loss, or degradation of wetlands and preserve and enhance the natural beneficial
values of wetlands in the conduct of the agency’s responsibilities. FEMA’s implementing
regulations for the EOs are at 44 CFR Part 9, which includes an eight-step decision making
process for compliance with this part of the Executive Order.
This eight-step process is being applied to the Spring Creek Flood Mitigation Project as the
proposed project is located in the 100-year floodplain of Spring Creek Tributary and a portion of
Spring Creek and includes activities in wetlands. The steps in the decision-making process are as
follows.
Step 1 Determine if the proposed action is located in the base floodplain and/or a wetland.
The Spring Creek Tributary Flood Mitigation Project involves culvert upsizing in conjunction
with increasing flow capacity of certain portions of the channel – Increasing culvert and channel
capacities with detention of increased flows at the end of the project within the identified base
floodplain/floodway (according to FEMA Flood Insurance Rate Map (FIRM) Lincoln County,
South Dakota, And Incorporated Areas; 46083C0159C and 46083C0157C, Effective date April
2, 2008).
A preliminary wetland assessment determined that small portions of Spring Creek Tributary
contain wetlands along its banks.
Step 2 Early Public Notice (Initial Public Notice).
Public Meetings were held throughout the project development process including meetings on
April 19, 2011, May 18, 2011, June 2, 2011, and July 28, 2011. Meetings were also held with
staff of Lincoln County Planning and Zoning, Geographic Information Services, Emergency
Management, The States Attorney, and Lincoln County Commissioners. There were objects
posed to the proposed project or comments that would substantially affect the design of the
project.
Step 3 Identify and evaluate alternatives to locating in the base floodplain and/or wetlands.
Alternatives to the Proposed Action consisted of Storm water detention at the beginning of the
project reach with minimized increases to culvert and channel capacities, individual mitigation
options (home retrofit, backfill and berms), allowing non-essential roads to overtop or be
removed and alternate access routes, and the No Action Alternative.
Cost estimates to modify the existing road crossings were determined to be comparable with
costs associated with road vacating and removal or construction of alternate routes while
providing the least interruption to established traffic patterns. However, alternate routes failed to
address flood damages and therefore were dismissed from consideration.
Individual mitigation options were dismissed as well. Although these actions could protect
individual homes, they would be voluntary and therefore not enforceable, they also could not
address any other flood problems in the area and affected homes would still likely have
insurance requirements. Additionally these options were considered as stop-gap solutions in light
of urban growth in the watershed while offering no relief to the regional problems with ponding,
culverts, roads, access, or erosion.
With the acquisition and demolition of structures within the existing 100-year floodplain
alternative, properties would be purchased and the structures demolished, thus removing them
from the floodplain. This alternative would reduce property damages associated with future flood
events, as there would be no structures within the floodplain that could be inundated by flood
waters. This alternative was considered to be cost prohibitive and unfavorable to the public. Plus
the alternative would not address flooding of the heavily used State Highway 392 and a busy
county road (Weld County Road 21).
Detention at the beginning of the project reach will reduce the risk of flood loss and minimize
the impact of floods throughout the entire project area, removing all but three homes from the
100 year floodplain. Additionally channel stability is expected to be restored and wetlands
enhanced by this alternative as well. Cost of this option is higher than the proposed alternative
due to the amount of land required and maintenance. Additionally, storm water runoff
conveyance for this alternative is governed by a 50 year event capacity at critical culverts and
therefore does not ensure the 100 year event conveyance capacity protection inherent to the
proposed alternative in more severe, multiple or “stacked” storm water runoff events.
No action will result in future repetitive and cumulative damages to homes, buildings, contents, personal
property, septic systems, roads, and infrastructure during flooding incidents within the project area. Issues
of erosion and sustainability are anticipated to increase due to regional growth potential.
Based on the alternatives analysis, it was concluded that the most practicable alternative to
reduce potential flood risks in the proposed project area would involve activities within the
floodplain/floodway and wetlands.
Step 4 Identify impacts of proposed action associated with occupancy or modification of the
floodplain.
Impact on natural function of the floodplain
Increasing the size and type of culverts, widening and deepening a portion of the existing
tributary channel, and creating additional water detention and storage at the end of the project
will not cause any encroachment to the floodplain. Any changes to the floodplain delineation due
to the projects will be submitted to FEMA for a LOMAR immediately following construction.
Impact of floodwater on the proposed facilities
All culverts installed as part of the project will be designed to convey the 100 year flood event
through them, thereby ensuring the vulnerability from storm water backup during this event is
removed. This action provides maximum protection from flooding resulting from storm water
backup by providing 100 year event conveyance capacity at the critical culverts
Impact on Wetlands
The proposed project will allow the wetland adjacent to the channel to function at or above their
current levels. Pre-construction wetland delineations will be done along the areas of channel
improvements and at each road crossing around culverts to be incorporated into the project’s
final design, limiting stream modifications within the wetland areas and stabilizing stream banks
using native grasses, turf reinforcements mat or erosion control blanket when practical.
Step 5 Design or modify the proposed action to minimize threats to life and property and
preserve its natural and beneficial floodplain values.
The Spring Creek Tributary Flood Mitigation Project would have no adverse impact on the 100year floodplain. Although construction of proposed project features would result in disturbances
within the base floodplain, none of the features are above-ground structures. Construction
activities are confined to increasing conveyance capacities within the channel of the existing
watercourse itself, therefore no encroachments are being constructed. The Project lowers base
flood levels throughout the project area below affected residence LAGs and eliminates road
overflow in a 100-year flood event at critical roads. Detention is provided at the end of the
project to restore additional volumes generated by the project to at least pre-project levels.
Approximately 22 residences, outbuildings and personal property within the project area will no
longer be impacted by a 100-year flood event. Potential for damages to infrastructure will be
substantially reduced and sustainability increased. Culvert increases ensure passage of the 100year flood event through all subdivisions, lowering the BFE below most residences and helps
ensure road access during a flood event.
The proposed project will allow the wetland adjacent to the channel to function at or above their
current levels.
Step 6 Re-evaluate the proposed action.
The proposed project will reduce the impact of the floodplain in the existing development
adjacent to the project are by increasing the storm runoff and drainage capacity of the project
area 100 year event level, in the process lowering base flood elevations in portions of the project
area. The Proposed Action will not facilitate development in the floodplain to any greater degree
than non-floodplain areas of the community. Additionally the project has been designed to limit
and mitigate any wetland impacts by limiting stream modifications within the wetland areas and
stabilizing stream banks using native grasses, turf reinforcements mat or erosion control blanket
when practical. Therefore, it is practicable to construct the proposed project within the floodplain
and wetlands, and the Proposed Action satisfies the identified purpose and needs.
Neither the No Action Alternative nor the other action alternatives that were evaluated are
practicable alternatives.
Step 7 Finding and public explanation (Final Public Notice).
After reviewing the environmental assessment prepared by Lincoln County and evaluating
existing conditions within the project area, FEMA has determined that there is no practicable
alternative to locating project features within the 100-year floodplain and wetlands of Spring
Creek and Spring Creek Tributary. This determination will be conveyed to the public in the final
public notice that will be published in the local newspaper.
Step 8 Implement the action.
The proposed Spring Creek Tributary Flood Mitigation Project will be constructed in accordance
with applicable floodplain development requirements and in accordance with applicable
regulations. A U.S. Army Corps of Engineers (USACE) Section 404 Individual Permit must be
obtained prior to beginning construction associated with the project. Compliance with all
stipulations stated in the USACE Section 404 permit is required for this project.