Sanderson Gulch Stormwater Improvements
Lipan Street to the South Platte River
The Sanderson Gulch stormwater project will improve the currently undersized drainage system between Lipan Street and the South Platte River. Once complete, the project will reduce flood risk in the area and nearly 100 structures will be removed from the regulatory floodplain as determined by FEMA. Local public infrastructure will be better protected and public safety risk during large storm events will be reduced. The project will deliver cleaner water to the South Platte River as stormwater will run through a multi-stage open channel with wetlands and a water quality vault. Finally, adjacent roadways, sidewalks/trails, parks and landscaping will be improved and the community will have a beautified, more enjoyable drainage corridor.
Construction of the new, higher-capacity drainage system will consist of underground, large-capacity stormwater box culverts (large pipes) to manage high-water flows during large storm events. The culverts will run underground between the southeast corner of Sanderson Park to the South Platte River, crossing under Lipan Street, the BNSF railroad tracks, and Platte River Drive. The culvert system will be combined with a naturalized, open-channel on the surface (between the railroad tracks and Platte River Drive) designed to convey and filter base flows and runoff from smaller storms and improve drainageway habitat. Hard landscaping will create a more visually pleasing inlet and outfall on both ends of the new stormwater structure.
PROJECT UPDATES — JULY 29, 2019
Construction on Sanderson Gulch will be largely completed and roads fully re-opened by the end of the summer, 2019. Revegetation, full restoration and recreational use of the gulch will take up to a year.
ONGOING SITE WORK
- S. Platte River Drive is closed between S. Huron Street and W. Florida Avenue. Local access to S. Huron and S. Inca Streets from S. Platte River Drive will be maintained.
- The temporary dam in the river that separates the Sanderson Gulch construction from the South Platte River will be dismantled by the end of July/early August.
- Construction of concrete box culverts. Concrete pumping machinery on site.
- Landscaping boulders are being moved into location.
- Levitt Pavilion has begun their concert series in Ruby Hill Park. Please observe signs directing concert traffic to the park entrance on W. Jewell Avenue.
- Ongoing construction and noise expected seven days a week.
- This is an active construction site. Pedestrians please observe sidewalk closures.
S. Platte River Drive and W. Florida Avenue Traffic Alerts
- S. Platte River Drive is closed southbound from S. Huron Street to W. Florida Avenue through the end of the construction project (late summer).
- Northbound traffic on S. Platte River Drive detoured onto W. Florida Avenue to S. Lipan Street.
- S. Jason Street remains open for business, but closed to through traffic.
- S. Huron and S. Inca Streets are open for business, and northbound traffic only.
The timing of traffic lights at S. Platte River Drive and W. Florida Ave has been adjusted to more efficiently move traffic through the construction zone.
W. Arkansas Avenue and S. Lipan Street Traffic and Trail Alerts
- S. Lipan Street at W. Arkansas Avenue is open.
- W. Arkansas Avenue will remain closed between S. Mariposa Street and S. Lipan Street for the duration of the project.
- Sanderson Gulch Park trails adjacent to the construction site are closed. Please observe ‘Trail Closed’ signs.
Extended Work Hours: Crews will be working and equipment operational Monday through Saturday from 6am to 10pm. Noise level monitoring will be in effect.
The existing underground stormwater pipes and open channel (stream or creek) are not large enough to safely drain water from major storms. In the event of a 100-year storm (a very large storm that has a 1 percent chance of occurring in any given year), the railroad, open channel, and South Platte River Drive are expected to flood, impacting nearly 100 properties.
Modifications to increase pipe capacity and improve the open channel are necessary to protect the area from flood hazards. The open channel will also naturally clean stormwater as it passes over porous soil and plant material. The project includes a water quality vault to catch larger trash and debris. Upon completion, the improvements will offer better flood protection for people and property. Cleaner stormwater will flow into the S. Platte River, and a more beautiful space will be created for the community to enjoy.
Construction began on January 29, 2018 with Denver Water lowering a large water line in South Platte River Drive. In February 2018 the City’s contractor, Wadsworth Construction, began work on the stormwater pipes and open channel.
- Partial closure of S. Platte River Drive in the project area will begin January 29, 2018.
- Starting in February, the northbound lane of S. Platte River Drive will be closed at Florida Avenue and traffic detoured onto Lipan Street.
- Starting in February, S. Jason Street at S. Platte River Drive will be closed, but traffic will have access to S. Jason Street businesses from W. Louisiana Avenue.
- The intersection of S. Lipan Street and W. Arkansas Avenue will also close during a portion of the construction project.
- In order to keep detoured traffic from entering the residential neighborhood, lanes on S. Platte River Drive will never be closed at the same time as the intersection of S. Lipan and W. Arkansas.
The corner of the park at S. Lipan and W. Arkansas will be closed and fenced during construction. This will be an active construction site with no public access.
Sanderson Gulch is like many other rivers throughout Denver that were used as dumping grounds for trash and construction debris during the early development of the City. As a result, the dirt or soil along the riverbank contains contaminants that will need to be mitigated as part of this project. Air monitoring and other safety measures per federal and state requirements will be strictly followed.
During construction the public may not enter the active construction zone and must follow posted signs and fencing.
The existing stormwater culverts and open channel have inadequate capacity for conveying major storm flows in the area. In the event of a 100-year storm (a very large storm that has a 1 percent chance of occurring in any given year), the railroad, open channel, and South Platte River Drive are expected to flood with potential to impact a large area of commercial, industrial and residential development on the north side of Sanderson Gulch, west of the South Platte River. Nearly 100 properties are located in the shallow flooding FEMA Special Flood Hazard Area (SFHA). As the drainage basin continues to develop and future stormwater infrastructure projects are constructed to direct more runoff to Sanderson Gulch, flooding risks will increase. Drainage modifications to increase capacity and improve water flow are necessary to help protect adjacent properties from flood hazards.
Upon completion of the Sanderson Gulch improvements, the combined culvert and open channel system will be a significant improvement over the current drainage. The new channel will allow for slower and shallower stormwater flows leading to enhanced ecology, water quality, and attractiveness of the area. The new underground culverts will have increased capacity to convey major storm flows and prevent localized flooding.
Before: Flooding areas in 100-year storm
After: Flooding contained within floodway in 100-year storm
A Federal Emergency Management Agency (FEMA) issues a Letter of Map Revision (LOMR) to revise the floodplain boundaries approximately 12 months after construction is completed. Property owners will then receive official notification of floodplain map changes once the new map becomes effective.
The surface-level, open channel will provide an improved connection to the S. Platte River, and naturally clean stormwater in Sanderson Gulch as it passes over porous soil and plant material. Additionally, the project will include a water quality vault to catch larger trash and debris. The water quality vault will be located on the west side of S. Lipan Street, just south of the new underground culverts. The vault will have a continuous bottom slope to prevent ponding water and a sloped trash rack to screen and collect debris. Vacuum trucks will periodically remove trash and debris.
At the South Platte River outfall, 6-inch to 18-inch pool depths will occur between the underground culverts and the landscape (boulder drop) structure. Periodically, sediment and debris will have to be removed.
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