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Jackass Hill Culvert Collapse

Project typeStreets
Project statusComplete
StartJune 2023
CompletionAugust 2023

Concrete pipes lined up and ready to install.

On June 12, 2023, following record-breaking rainfalls, two 48-inch diameter corrugated metal pipes in the Jackass Gulch stormwater culvert under Jackass Hill Road, just north of Mineral Avenue, collapsed. The old pipes, originally installed in 1985, are being replaced with two 66-inch diameter reinforced concrete pipes, which are far more durable. The increased size will also help handle much greater flows going forward.

On average, Littleton gets about 14 inches of rain a year, but by the start of July, the city had received more than that. Rainfall in June alone was four times the average. This has left the ground saturated and caused further debris collapse into the damaged area, though crews have been working quickly to overcome it.

Crews hope to complete the project and reopen the road by mid-August, but continued record-breaking rainfall has slowed progress. Thankfully, contractors were able to obtain the larger concrete pipe quickly. Normally, pipes of this size require months to fabricate, which would have pushed the reopening into the fall.

Replacement of these culverts and the need for a larger size were already being studied as part of an update to the Jackass Gulch Master Plan and designed as part of the Mineral Mobility Improvements Project, planned for 2024. Design was far enough along to use this information for replacement of the culverts now, rather than to undertake a temporary solution only to dig up the area again in a year. This accelerated the design of the emergency project by many weeks.

Detour Maps

Driving Detour Map(PDF, 1MB)
Bike/Pedestrian Detour Map(PDF, 441KB)

Below is a timeline of the construction progress. The timeline will be updated at major milestones.

Week of August 21

Final construction has been completed and Jackass Hill Rd. is now open

Week of July 31 to August 9

Channel grading work has progressed. The upstream and downstream channel work is complete.
The site will be restabilized with seed and erosion control blankets in the next few days
The west sidewalk was poured 8/9 and will be open for pedestrian and bike traffic Friday afternoon
The Denver Water Main leaked from upstream into the site and had to be mitigated. Repairs at Curtice were completed on 8/9.
This next week we will continue to install the last few segments of pipe once the water main issue is resolved and the inlet is in place. Pending no further delays, the east sidewalk and asphalt placement is expected late next week.
We anticipate the road to be fully opened to traffic in the later half of August

Week of July 24

The two 66-inch pipes have been installed across Jackass Hill Road.
Channel work has begun, but rain continues to be an obstacle making for sloppy site conditions (including getting some of the equipment jammed for a short time).
A 36-inch reinforced concrete pipe (RCP) will be installed across Jackass Hill Road through next week, replacing two pipes that were damaged by the culvert collapse Once the RCP is installed, street rehabilitation work can begin.
Positive news came in early this week on potential state and federal assistance for this project and for the two other collapsed culverts in Littleton. In partnership with Arapahoe County, other counties, and the State of Colorado, an emergency declaration was declared this week for the storm event that initiated Littleton's three collapses. The declaration will allow the entities to work collectively to apply for FEMA emergency funding reimbursement.

Week of July 17

The team continues to make significant progress, although Mother Nature continues to challenge everyone’s efforts. The nearest rain gauge to the site monitored by the city registered 0.94 inches Thursday.
Installation of the 66-inch pipe across Jackass Hill Road is mostly complete. Weather permitting, crews will install an additional 36-inch pipe across the road later this week. This will replace a 27-inch outfall and 18-inch pipe that was damaged during the initial culvert collapse.
In the past week, the project encountered an issue with a Denver Water line. Denver Water replaced a valve on Jackass Hill Road at Curtice, which resulted in some road damage. That has been fixed.
Once the stormwater components are complete, we will likely see work on the road begin in earnest in the next 10 days, weather permitting. The team is focused, even with the weather challenges, on getting the road open before school commences.

Week of July 10

The contractor spent half the day on Monday cleaning up from the weekend storm.
When the culverts originally collapsed, there was a significant void below the 16-inch water main that crosses the culverts. Denver Water had stated they shut down the water line at the start of the excavation in June. However, when the water main pipe was removed on July 10, crews discovered some water was still flowing through the water main. Denver Water crews were unable to completely close the valve to isolate this segment of the water main. This caused water from this water main to continue to saturate the site for two days until another valve could be closed on July 12.
Storm sewer infrastructure that drains stormwater from Jackass Hill Road was discovered to have been connected to the old CMP culverts, and this was also damaged during the culvert collapse. Staff has worked to redesign this storm sewer system into a configuration that will allow for effective maintenance in the future. The design is complete, and the materials have been ordered so the newly designed system can be installed as soon as the 66-inch pipes are functional.
Project delays due to weather, water main leaks, and other unforeseen circumstances have pushed the schedule out another two weeks. Staff anticipates having the road open by August 14 to meet the Littleton Public Schools start date of August 15, weather permitting.

Week of July 3

Heavy rain the evening of July 4, resulting in another lost day of productivity on July 5.
Dry days on July 6 and July 7 allowed the contractor to install approximately 50% of the new concrete culverts.
Heavy rain again on the evening of July 8 caused overtopping of the temporary dam and filled the new culverts 25% full of rock and sediment.

Week of June 26

The site remained significantly saturated after all the previous week’s storms. The first two days of the week were spent cleaning up.
The first few segments of the new concrete pipe were installed.
Rainfall three days this week continued to saturate the site and slow progress.

Week of June 19

The contractor created a dam to bypass Jackass Gulch from the work site.
The 66-inch concrete pipe was delivered to the site.
Existing sanitary sewer and water main were secured through the project site.
The contractor placed the first later of rock bedding for the start of new pipe installation early in the week.
Heavy rain fell the evening of June 21, overtopping the temporary dam built to hold back water, and damaging the bypass pump.
A major flooding rainfall event (approximately a 25-year storm) occurred on June 22, causing serious damage. All previous excavation and site preparation work was severely damaged.

Tuesday - Friday, June 13 - 16

C&L Water Solutions mobilized equipment to the site. Pumps were set up to divert stormwater around the culvert collapse.
Excavation of the site and collapsed culverts began.
Heavy rains on the evening of June 15 caused ponding upstream of the project site and additional erosion through the culvert area.
The contractor spent most of the day on Friday, June 16, cleaning up from the previous rain.
Heavy rain again on June 16 caused more erosion and damage at the site.
Staff monitored the site over the weekend for safety.

June 13

Chain link fence was installed to enhance the safety of the immediate area.
A pedestrian/bicycle detour route was established along the railroad spur trail to the west of Jackass Hill Road and through streets in the Palisade neighborhood. This route is only dirt trail.
C&L Water Solutions was able to procure the necessary pipe to replace the old culverts with two 66-inch diameter concrete culverts. This was surprising to everyone involved, as this size of pipe is not typically readily available and usually would take many weeks to fabricate.
C&L Water Solutions plans to begin replacement of the culverts starting Monday, June 19.
The estimated timeline for full replacement and roadway restoration is unknown at this point but is likely to be weeks.

June 12, 2023

A sinkhole appeared on the surface at approximately 9 a.m. As rain continued, the sinkhole increased in size and further eroded the soil below.
City staff investigated the site and found that the northern culvert was fully blocked with sediment, but the southern culvert was still flowing.
Jackass Hill Road was fully closed from West Mineral Avenue to South Curtice Street.
At approximately 1 p.m., staff met with C&L Water Solutions on-site to assess the damage and start to formulate a repair/replacement plan.
Rain continued, and the sinkhole continued to grow larger.
The southern culvert became visible, and it was clear that this had failed also.
Denver Water shut off the 16-inch water main, which crosses above the culverts.
An inspection at 4:30 p.m. revealed that the southern culvert had collapsed so that no flow in Jackass Gulch was passing through either culvert.