Sioux Falls Downtown River Greenway

Challenge

The project is located in the floodway of the Big Sioux River. Federal Emergency Management Agency (FEMA) requirements would not allow an increase in the 100-year floodplain elevation, so the design needed to accommodate a widened trail and substantial gathering spaces without resulting in a net rise in the floodplain. In addition, a 60-in sanitary sewer main was located just under the trail on the east side of the river. Although located in the downtown area, the project area on the east side of the river was historically difficult to access for two reasons: (1) access from the east side of the river was limited by stairs or steep slopes since the trail was 10 ft below adjacent roads, and (2) since much of the downtown’s development is located on the west bank, there was no direct pedestrian access to the east bank trail.

Solution

The renovated trail was set at the 5-year floodplain elevation, slightly lower than the previous trail’s elevation. In order to widen the trail and create plaza spaces without adding fill or disturbing upland utilities, a river-edge wall was added. To improve river access, steps down to the river’s edge were incorporated at intervals along the wall. The pedestrian trail elevation could not be raised due to floodway restrictions, but sloped walkways were added to accommodate bike traffic and accessible routes. To facilitate pedestrian access from the west bank, an abandoned railroad bridge was removed and replaced with a single-span pedestrian bridge. 

• 1,550 ft of bike and pedestrian trails provide recreational opportunities. 
• The amphitheater includes 14 benches that provide up to 192 ft of seating flanked by an arc-shaped stone wall projecting into the river.
• A 200-ft-long pedestrian bridge replaced an abandoned railroad bridge that acted as a dam during flood events. This was required to provide additional design flexibility and to accommodate bikes and accessible access to the trail. It also serves as a bypass during storm events that impede trail use.
• A canoe and kayak landing provides access for aquatic recreation.  
• A river overlook provides attractive views.  
• A plaza space features a unique interactive water feature.
• Local quartzite stone was used to construct the center amphitheater and incorporated as an accent throughout the project. The 8 quartzite pillars surrounding the amphitheater were created by a local artist.
• Form liners were used on cast-in-place concrete surfaces for a more attractive look. 
• Native and hardy plant material was utilized throughout the project including sumac (Rhus), spirea, coneflower (Echinacea), black-eyed susan (Rudbeckia hirta), sedum, big bluestem (Andropogon gerardi), switchgrass (Panicum virgatum), little bluestem (Schizachyrium scoparium), and prairie dropseed (Sporobolus heterolepis). Plantings help soften the walls that were needed for the construction of the sloped walkways.
• Educational panels along the trail provide visitors with historical and environmental information about the river and downtown Sioux Falls.   

Local quartzite was roughly double the cost of brick, a more conventional choice. The estimated material cost for brick was $45,375; installation cost would have been $117,623. Although the cost of the quartzite was significantly more than an alternative material, the quartzite provided a regional feel and was used throughout the project. Quartzite was a more sustainable choice than brick or cultured stone because it reduces transportation costs and supports the local and regional economy. Some brick was used in phase 2 of the project to save costs and match adjacent buildings. 

• Sioux quartzite, a local stone, was used for many aspects of the project, including large capstones on the river’s edge. The stone is sourced from a relatively small region at the juncture of South Dakota, Minnesota, and Iowa. Color variation in Sioux quartzite ranges from maroon to light rose, and the stone is very hard (a 7.5 to 8 rating on the MOHS scale). The quartzite was mortared in place, but joints began to fail immediately after installation due to expansion and contraction. Mortared joints were replaced with caulked joints.  
• With a lump-sum design-bid-build delivery method, several additional unseen conditions for construction below grade impacted the Phase 1 project cost. For Phase 2 of the project, unforeseen conditions were better accommodated to allow construction of the water feature. Unit prices and allowances were included in the project for all below-grade construction activities such as rock excavation, unclassified excavation, soil disposal, lean concrete fill, concrete footings, and concrete foundation walls. This took some of the burden of estimating unknown factors off of the bidders and set forth a payment procedure for bid items where quantities were likely to vary during construction.
• The river walls were designed to be supported on bedrock elevations as indicated in geotechnical investigation reports and construction records from the 60-in sanitary sewer installation project. In Phase 1 of project construction, excavation found that bedrock had been disturbed and replaced with fractured rock over the past century due to blasting for earlier bridge and sanitary sewer installations. Dewatering and excavation to sound bedrock was not possible, as this would undermine the 60-in sanitary sewer main located within feet of the proposed river wall. Ultimately, helical anchors drilled to bedrock were used to support a concrete footing under the river walls, resulting in project delays and additional costs. During Phase 2 of the project, instead of geotechnical borings, test holes were dug along the extent of the proposed river wall during the design phase to get a much more accurate idea of conditions that would be encountered.

Pedestrian Walkway Lighting: Sternberg A753ASR
Wall Lighting: Bega 2384LED
Bollard Lighting: Kim VRB3
Channel Drain: Zurn Z886
Green Roof: LiveRoof
Irrigation: Rain Bird
Benches: DuMor, Inc 160 Series
Trash & Recycling Receptacles: Victor Stanley S-42
Bike Racks: Forms + Surfaces Bike Garden
Stone: Sioux Quartzite, L.G. Everist Inc.
Brick: Endicott Clay #46 Medium Ironspot Velour Grade
Interpretive Sign Panels: Fossil Industries
Pedestrian Bridge: Big R Bridge
Water Feature: Delta Fountains
Retaining Wall: Anchor Highland Stone
Helical Piers: Atlas Foundation

Project Team

Landscape Architect: Confluence
Geotechnical Engineer: Geotek Engineering & Testing Services, Inc.
Structural Engineer: Structural Engineering Associates
Civil Engineer: Goldsmith Heck Engineers, Inc.
Electrical Engineer: Associated Consulting Engineering, Inc.

Role of the Landscape Architect

The landscape architect was the prime consultant for the City of Sioux Falls and was fully responsible for permit approvals, site design, and construction detailing. The landscape architect also provided construction administration services. Numerous meetings were held with the public and adjacent landowners during design and construction of the project. For permitting, the landscape architect worked with the South Dakota Regulatory office of the U.S. Army Corps of Engineers; the U.S. Fish and Wildlife Service; South Dakota Game, Fish, and Parks; and the South Dakota Department of Environment and Natural Resources.