Fountain Creek at Southmoor Drive
An investigation of fluvial hazards
The Southmoor Drive project along Fountain Creek will work to provide bank stability to protect local infrastructure and minimize sediment introduction. This project is led by the Fountain Creek District, whose goals for the Creek center around creating a culture of conservation through three main avenues of funding, infrastructure, and outreach. The District also oversees water transport and reclamation projects along Fountain Creek from Colorado Springs to Pueblo. This is important because the city of Pueblo relies on clean and sediment-free water delivered through Fountain Creek for its drinking water. Here, we use the Colorado Fluvial Hazard Mapping protocol, a statewide project aiming to create resources and systems for stream mapping throughout Colorado, to investigate the history and current fluvial hazards at the Southmoor Drive site as context for the District's work.
Historic channel movement
Active channel in 1937 (left) and 2023 (right) with the 2023 centerline for reference on both images. Location is upstream of the Southmoor Drive study area.
Historically, Fountain Creek was a mobile channel, as seen in the slider images above. Traces of the 1937 channel can still be seen in the modern topography, present as strands of cottonwoods and lower elevation regions of the floodplain. The active zone of the channel, seen in the bare gravel bars, was wider in 1937 and has since narrowed, while the location of the main channel has migrated, often up to 100 meters.
As we'll explore below, modifications to the landscape have confined Fountain Creek and created a less mobile channel.
Changes to Fountain Creek
Aerial imagery of the study region from 1937 (left) and 2023 (right)
Aerial images of the study region from 1937 and 2023 illustrate the increase in development, channelizing Fountain Creek into a narrow meander migration belt and adding impervious surfaces. The 1937 image shows that the channel was braided and laterally migrated freely, partly as a result of the local geology. Fountain Creek at Southmoor flows through shale and assorted river sediment deposits. This bedrock is easily weathered and eroded and facilitates rapid lateral migration; it also poses a potential sediment hazard due to the rapid erosion possible.
Effects of Development
This map shows impermeable surfaces in the Southmoor region. Black shows permeable surfaces where water can infiltrate into groundwater systems, and the pink to fuchsia gradient shows increasing surface impermeability where stormwater tends to runoff directly into the stream.
A large amount of impermeable surfaces to the south and east of Southmoor (noted by the brown dot) allow precipitation to travel rapidly into Fountain Creek. This increases the flashy behavior of the stream and can increase erosion and flood rates.
Alongside the impervious surfaces, the land use around Southmoor is highly developed. The map at right shows that most of the landscape is low to medium development. Combined with the high density of impermeable surfaces to the east of the site, this development further heightens risk of flashy flows and flooding.
Channel confinement between I-25 to the west and US-85 to the east prevents large-scale channel migration; while this helps decrease erosion risk, it channelizes flood waters in a much narrower zone than historically (see the 1937 imagery) and could increase the severity of floods.
The large area of grassland to the southeast of the study region, on the protected Fort Carson property, aids groundwater infiltration and wetland preservation.
Defining fluvial hazards in the modern channel
We used the Colorado Fluvial Hazard Mapping protocols to define the active stream channel in Fountain Creek. This classification relied on historic photos, 2023 aerial imagery, and high-resolution topographic models to estimate the extent of active river influence. This active stream corridor defines an area of high river usage; we note that this is not the same as the flood risk zone, which is a much more expansive region!
One of the datasets we used is a relative elevation model of Fountain Creek. This colors the landscape by height above the river and highlights floodplains (green) and terraces (red-yellow) at the Southmoor project site.
Our final active stream channel is shown in purple. This includes all regions that show evidence of repeated river occupation. Note that the active stream channel is narrow through the Southmoor site; while this means the zone of active stream erosion is small, it also implies that floodwaters are initially constrained to a very small region and may be more erosive.
Southmoor Project
What does this mean for the Southmoor Drive project?
Slider showing proposed bank stabilization project. Colors show the slope of the landscape.
In the study area, increased urbanization since 1937 has resulted in a narrower stream channel. The combination of more impervious surfaces and an easily erodible bedrock suggests the region is prone to erosion and sediment transport. Our active channel mapping also suggests that the narrow active channel zone could lead to increased erosion within that zone, as floodwaters cannot initially spread out.
Therefore, the proposed project at the Southmoor Drive targets a key area for erosion control. The plan to reduce the bank slope on the outer bend will protect local infrastructure from flooding and erosion. Likewise, the maintained floodplain on the west side of the project site allows for overbank water flow and sediment deposition. Together, the reinforced outer bank and maintained floodplain prevent further erosion and sediment transport while facilitating sediment deposition.
