Ralston Creek Improvements

Background

The City is partnering with the Mile High Flood District to improve the stream corridor health, stability and flood-carrying capacity of Ralston Creek near the Westwoods subdivision, just west of the Croke Canal crossing. This area was heavily impacted by the September 2013 floods, resulting in damages to the stream corridor, surrounding property and breaches of the Croke Canal embankment.
 
This stream stabilization project will:
  • Increase the flow capacity of the creek where it crosses over the canal.
  • Replace the current pedestrian bridge with a larger structure so it does not constrict the floodplain.
  • Improve the layout and safety of the Ralston Creek Trail.
  • Integrate natural, aesthetic and resilient channel design features.
  • Remove dead and overgrown trees that constrict the floodplain corridor and create increased flood and pedestrian risk.
  • Strategically plant new trees that can provide better wildlife habitat without impacting natural stream flows.
The City takes the health and well-being of all wildlife very seriously. The project team is working closely with an environmental consultant, the Army Corps of Engineers, and the U.S. Fish and Wildlife Service to survey, mitigate and protect all animal species and their habitats that may be impacted by the project.


Watch this YouTube video to learn more from the project managers.

Future Design Concept

Plan View

Plan View

  1. Re-aligned Ralston Creek
  2. Soft surface trail
  3. Recreational logs + boulders
  4. Re-aligned multi-use path
  5. Seating / gathering area
  6. New pedestrian bridge
  7. Existing trees to remain
  8. Planted trees
  9. Secondary channel
  10. River stability structure with seating
Ralston creek at croke work zone
View A

View A: Looking west from bridge

View B

View B: Looking southeast from multi-use trail

View C

View C: Looking east from creek

Project Updates

  • April 2023: Pre-construction tree clearing of dead and overgrown trees. 
    • These trees pose a significant flood risk in the area. 
    • Environmental consultants and ecologists conduct bird and nest surveys to identify trees that cannot be removed to protect wildlife. 
    • No active bird nests were observed throughout the study area or within 50 feet of the study area. No active raptor nests were observed throughout the study area or within 0.5 miles of the study area. 

Before and After Photos

Before and after photo of tree clearing near project area
Before and after photo of tree clearing near project area
Before and after photo of tree clearing near project area
Before and after photo of tree clearing near project area
Before and after photo of tree clearing near project area
Before and after photo of tree clearing near project area

Timeline

  • Quarter (Q)1 2023: Pre-construction tree clearing (complete)
  • Q3 2022 to Q3 2023: 60% Design, Environmental Survey and Permits, and Floodplain Permits (in progress)
  • Q4 2023: Final Design and Permit Approvals*
  • Q1 to Q2 2024:Construction*
    • Trail closures will be necessary during construction (more information will be made available)
    • Approximately 5 to 6 months of construction
  • Q2 / Q3 2024: Re-vegetation and plantings*

*Timelines are approximate and dependent on weather and permit approval processes.

Project Goals

  1. Flood Conveyance
  2. Public Safety
  3. Tree Health
  4. Recreation
  • Remove dead and down trees, invasive tree species, and thick vegetation that are impeding the flow of water during heavy rainfall or flooding events
  • Facilitate the natural movement of water
  • Analyze where the channel improvement grading will significantly disrupt the tree canopy zone or directly affect the tree trunk and thus the well-being and longevity of trees
  • Mitigate potential harm to the existing tree root systems, structural integrity, and overall health of the trees to remain

Additional Background Information

Prior to this work beginning, the City team evaluated multiple options for how to best mitigate the flood risk through this corridor. 

The current state of the creek had flood carrying capacity for a 2 to 10-year flood event (10 to 50% chance in any given year). The creek should be designed for a 25 to 100-year event (1 to 4% chance in any given year).

The project is designed to have flood carrying capacity for a 25-year event, based on the following factors:

  • Mitigation of impacts and disturbance to the tree and creek environment
  • Flooding risk to the surrounding homes, infrastructure, trees and stream
  • Cost and resource allocation for the project
  • Impacts to FEMA floodplain elevations

The project team went through several iterations of design to try to avoid tree removal. However, due to the proximity of these trees to the creek it was deemed necessary to remove trees to realign and restore the stream corridor. 

Replanting and Revegetation

The area will be restored with replacement trees and natural features once construction is complete in spring 2024. Revegetation will be designed in a manner that is more sustainable to the possible flooding events, including the replanting of trees in safer locations. 

Tree replacement and revegetation is not a one for one replacement. Often, replacement results in more trees and vegetation to revitalize an area.