To: Honorable Mayor and Members of Town Council
From: Mark Marlowe, P.E., Utilities Director
J. David Van Dellen, P.E., Stormwater Manager
Title
Update: June 2015 Flood Damage Report
Body
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Executive Summary
The purpose of this memo is to update Town Council on flood damage that occurred in early June of this year. Town of Castle Rock rain gage data recorded between 3 and 5 inches of rain over a three day period from June 10 to June 12. This, in addition to above average moisture conditions this spring, resulted in flood damage to East Plum Creek, Tributaries and several reports of flooded basements. The Utilities Department, along with other departments, is responding to several unplanned and unbudgeted issues to address the flood damage to public utilities and trails. The estimated cost for Utilities to respond to damage caused by this series of storms is $1.625 million. The design of several emergency repair projects are currently underway using budgeted contingency funds and planned reserves. Staff will report back to Council and bring the designed and bid projects for consideration as part of the third quarter budget amendment for the allocation of funds to complete the repairs as needed.
History of Past Town Council, Boards & Commissions, or Other Discussions
On June 2015, staff provided a preliminary flood damage report to the Utilities Commission.
Discussion
Below is a summary of projects that require immediate action to address flood damages and to protect public utilities, trails and adjacent property.
East Plum Creek Water Line Protection at Perry Street - A 12” waterline that crosses E. Plum Creek near the future extension of Perry Street has been exposed along the west bank of the stream. The line does not appear to have been damaged, however it is isolated until repairs are completed. The water line which was installed in the 1980s became exposed due to a lateral shift in the stream that cut into the west bank. The water line will need to be lowered to account for the new stream alignment at a cost of approximately $150,000. This project is being funded through Water in 2015 from realignment of budgeted capital projects.
East Plum Creek Water Line Protection at Meadows Pkwy - A 16” waterline that crosses E. Plum Creek at the Meadows Parkway overpass has been threatened due to the failure of downstream grade control. The floods on June 12 caused E. Plum Creek to rise above its banks resulting in the failure of the sheetpile cutoff wall installed to protect the waterline in the 1990s. The downstream grade control will need to be reconstructed and a formal drop structure will be installed downstream of the waterline crossing. This improvement is identified in the Stormwater Master Plan; however the project was not budgeted until 2022. The estimated cost of this project is $500,000 and will be funded through the Meadows Capital Reserve and Stormwater Capital Reserve.
Omni Tributary Bank Stabilization at Epiphany Lutheran Church - This section of Omni Tributary is in a natural unimproved state. The channel located on Town property has shifted laterally impacting private property. This section of drainageway is planned to be stabilized through an adjacent development project in the future. An interim repair is needed to shift the channel back onto Town property and restore the banks of the adjacent church property. The estimated cost of this repair is $25,000 and will be funded through the 2015 Stormwater Contingency account.
Industrial Tributary Sanitary Sewer Protection at Topeka Way - A sanitary sewer manhole was exposed along the north bank of Industrial Tributary as a result of the June floods. This section of Industrial Tributary requires a realignment of the drainageway and grade controls structures to protect the utility. The estimated cost of this project is $300,000 and has been included in the 2016 Stormwater capital budget.
Heckendorf Regional Detention Pond Repairs - An existing dual 42” storm sewer that outfalls into the Heckendorf Regional Detention Pond failed in the fall of 2014. Approximately 70 linear feet of storm pipe has collapsed along the banks of the pond. An interim repair was installed in early 2015 protecting the system from further damage during the June storms. However, a permanent reconstruction of the storm sewer is planned for this fall. The estimated cost of this project is $300,000 and is being funded through Stormwater in 2015 from realignment of budgeted capital projects.
Hangmans Gulch Trail Protection - The Stormwater Division partnered with the Parks Department in 2011/2012 on the Hangmans Gulch Trail and Channel Improvement Project. Due to limited funding, only a portion of the planned stream channel improvements could be installed to support the new trail. Since that time, Hangmans Gulch has experienced several flooding events that migrates sediment downstream impacting certain portions of the trail. In June, the stream shifted laterally in two locations undermining the new trail. Town crews are actively working to protect the trail and remove sediment at locations that impact recreational users. The estimated cost of this work is $55,000. Additionally, the next phase of stream channel improvements is needed sooner than originally calculated. An original $900,000 was budgeted from stormwater capital reserves in 2016, however only $350,000 remains to be allocated to this project after accounting for the above projects.
Budget Impact
An estimated $400,000 is needed from the Water Fund and $1.23 million from the Stormwater Fund to address flood damages. The Water Fund has an estimated $6 million in the Meadows Capital Reserve along with other capital projects that have been realigned to provide the needed funding. The Stormwater Fund has an estimated $1 million in unobligated reserves along with other capital projects that have been realigned to provide the needed funding.
Staff Recommendation
Staff recommends completing designs and bidding projects to repair various damages over the next several months. Once bids are obtained, staff will bring the projects back to Council for consideration using funding from planned contingencies, fund reserves and undesignated fund balance from the stormwater and water funds to address flood damages to East Plum Creek and its tributaries for the protection of public utilities, trails and adjacent property.