INCIDENT AND FOLLOW-UP INSPECTION REPORT

Dam Name:

Chambers Lake

DAMID:

030115

PROJECT INFORMATION Dam Safety Engineer: Date:

Other:

June 10, 2016

Time on Site: INSPECTION PARTICIPANTS

Dam Owner(s): Water Commissioner:

KEB

Water Supply and Storage

Contacts:

Jim McFall Dennis Harmon

Mark Simpson CONDITIONS

Reservoir: Weather: Ground Moisture:

Gage height 46.3 Raining but anticipated to stop tonight Saturated INCIDENT DESCRIPTION

Date Received a call from Mark Simpson on June 8, 2016 at 8:00am reporting that Chambers Lake spillway was flowing (spilling). Next received a call from Dennis Harmon reporting that the spillway at Chambers was flowing (spilling). Chambers is a high hazard dam up the Poudre Canyon with a large spillway and 9 feet of freeboard. Dennis said they had an error on their Sutron remote sensor. The Sutron said they had 11 feet of storage still in the reservoir. Water Supply & Storage had a gotten call from Joe Wright reservoir guys reporting Chambers was spilling. Water Supply Employee then tried to reach site from the north but could not because the Larimer river road was washed out and spillway was flowing. Dennis then called another worker to reach site from south and open the gate. Dennis reported he had called Larimer County Sheriff and Larimer county road and bridge department. INCIDENT RESPONSE June 8, 2016 I called and left message for Lori Hodges, Larimer County Emergency Manager, saying that Chambers Lake was spilling which is an unusual condition but is not a dam safety concern and dam is performing as expected and to

810 9th Street, suite 200, Greeley, CO 80631 P 970.352.8712

Page 1 of 11

F 970.392.1816 www.water.state.co.us

Chambers Lake Incident and Follow-Up Inspection Report (030115) June 10, 2016 Page 2 of 11 call if she had any questions. Explained the owner had contacted sheriff and county road and bridge department. Then called Kevin Kurteich, Regional State Emergency Manager and reported incident. Then spoke with Randy Gustafson with City of Greeley to see if his workers were up the canyon and if he could contact them to observe the reservoir. He did not have radio with his personal up the canyon they can call but not receive calls. I then tried Ross Lamb, City of Fort Collins personnel and was unsuccessful at reaching him. Water Supply called and said they had reached the dam and the outlet was opened. 3:30pm Randy called and said that his inspectors had seen that Chambers Reservoir was flowing and Larimer River road was washed out. Water Supply and Storage was releasing 350 cfs out of the gate Chambers Lake stopped spilling around 4:00pm. June 9, 2016 I spoke with Jim McFall to get update on conditions at Chambers. Jim said it was not spilling the outlet is open but lowered rate to about 200 cfs. I called Lori Hodges, Larimer County EM, to give an update. June 10, 2016 I went up to dam to inspect condition and record how dam had performed. OBSERVATIONS Reservoir gage height 46.3 which is about 0.7 below the spillway (Photo 1). Spoke with Water Supply & Storage employee Grizz. He reported that the water flowed about 3 feet deep. There is a stake on the spillway showing the highwater mark. The stake appears closer to 1 feet deep. This is the highest known water surface elevation and consistent with visual indicators such as grass that is laid down. The spillway rating curve shows one foot of flow is 786 cfs and 2 feet of flow is 3,653cfs. The water flowed around the corner and then down into the channel. It then ran and apparently split in the woods and ran overland flow through the channel and down onto the road. The south drain was trickling below the weir. It appears to be leaking out bottom The north drain was reading 0.29 after cleaning algae in a 90- degree v-notch weir The lower drain was reading 0.44 a 90-degree v-notch weir Outlet drain 0.19 The spillway shows signs of having water run through it. The spillway is stepped with 300 feet at gage height 47.1 and 440 feet at 48.1.The spillway ran on the east side which is 1 foot lower and the water appeared to extend at least 40 feet into the rocks on the spillway. There is large head cut downstream where the spillway drops into the natural drainage. The cut is about 8 feet deep. The bottom of the channel was saturated and made it difficult to walk. Walked in on the Larimer River Road and spoke to Jim Frick, Non-paved roads group manager. Jim was on site while spillway was spilling and showed pictures on his phone. The Road cut was at least 6 feet deep. The water ran over the hillside and down onto the road. He said it was too deep and fast to walk across. The snotel site was filled with rock and sand.

Chambers Lake Incident and Follow-Up Inspection Report (030115) June 10, 2016 Page 3 of 11 CONCLUSIONS AND ACTIONS Conclusions The dam does not show signs of distress. It appears the spillway functioned as designed. The head cutting is downstream of the spillway. Recommended and Executed Actions to Date The reservoir continues to lower the reservoir elevation. The owner is trying to lower the reservoir to gage height 46. This would be about 1 foot below the spillway elevation. The toe drains should be read frequently until the reservoir is brought down to a typical gage height and the drains are reading more typical numbers. Water Supply & Storage is getting the sutron repaired so it accurately reads.

Photo 1. Reservoir gage height 46.3, which is about 0.7 below the spillway

Chambers Lake Incident and Follow-Up Inspection Report (030115) June 10, 2016 Page 4 of 11

Photo 2. Looking across the spillway from the dam

Photo 3. East side of spillway where water ran, looking downstream/north

Chambers Lake Incident and Follow-Up Inspection Report (030115) June 10, 2016 Page 5 of 11

Photo 4. Spillway concrete cutoff wall on east side where sediment was deposited on the concrete.

Photo 5. East side of spillway standing where the head cut began looking upstream/south

Chambers Lake Incident and Follow-Up Inspection Report (030115) June 10, 2016 Page 6 of 11

Photo 6. Spillway standing at section where one foot low looking west

Photo 7. Spillway looking east. Rod indicates high-water mark

Photo 8. Standing in spillway at section that is 1 foot higher looking upstream/south

Chambers Lake Incident and Follow-Up Inspection Report (030115) June 10, 2016 Page 7 of 11

Photo 9. Spillway looking southwest shows where some water laid down grass

Photo 10. Standing in spillway looking downstream/north as water returns to drainage

Photo 11. Standing in drainage looking up at large gulley in spillway channel, looking upstream/south

Chambers Lake Incident and Follow-Up Inspection Report (030115) June 10, 2016 Page 8 of 11

Photo 12. Spillway channel, looking downstream/north standing down in channel

Photo 13. Spillway channel, looking upstream/south subgrade beneath rock was saturated

Photo 14. Larimer County Road 103, located downstream of spillway. Looking uphill/north after major repairs underway

Chambers Lake Incident and Follow-Up Inspection Report (030115) June 10, 2016 Page 9 of 11

Photo 15. Downhill from Larimer County Road 103. Water from spillway flowed in this area, destroying a snotel site

Photo 16. Downstream outlet structure with 350 cfs being released

Photo 17. Southern toe drain showing clear and typical conditions. No issues

Chambers Lake Incident and Follow-Up Inspection Report (030115) June 10, 2016 Page 10 of 11

Photo 18. Northern toe drain showing clear and normal conditions, no issues

Photo 19. Lower toe drain showing clear and normal conditions, no issues

Photo 20. Picture from Larimer County Road and Bridge Department showing the water that was flowing overland onto the Larimer River Road

Chambers Lake Incident and Follow-Up Inspection Report (030115) June 10, 2016 Page 11 of 11

Photo 21.Photo from Larimer County Road and Bridge showing water going over Larimer River Road

Photo 22. Photo from Larimer County Road and Bridge department showing water running onto road and down the road