Title
Discuss and Provide Direction on a Revised Drainage Maintenance Policy and Priority Matrix and Discuss and Provide Direction Regarding Creek Erosion Issues Raised by the Residents of the Westwood Park Addition
Summary
COUNCIL GOAL: Enhance the Quality of Life in McKinney
MEETING DATE: September 19, 2016
DEPARTMENT: Development Services / Engineering
CONTACT: Mark Hines, PE, Director of Engineering
RECOMMENDED CITY COUNCIL ACTION:
• Approval of the revised drainage maintenance policy and priority matrix.
• Provide direction regarding creek erosion issues raised by residents of the Westwood Park Addition.
ITEM SUMMARY:
• Based on input received at the July 18, 2016, City Council Work Session, staff has revised the drainage maintenance policy and priority matrix. Staff is now seeking approval of the policy and matrix.
• In light of the revised policy and matrix, staff is also seeking direction about how to address the issues raised by residents of the Westwood Park Addition.
BACKGROUND INFORMATION:
• Regarding the policy and matrix:
o Citizens frequently contact City staff about various drainage issues.
o Typical concerns include flooding, creek erosion, lot to lot drainage, poor drainage, standing water, fallen trees, and overgrown vegetation.
o Every situation is different and some cases are more severe than others. The revised policy is intended to clarify what role the City has in addressing these drainage concerns. The revised matrix is intended for use only after a particular concern has been deemed to be City responsibility. It will be used to determine the priority of various City projects.
• Regarding the creek through the Westwood Park Addition:
o Several Westwood Park residents have come together to ask City staff to address erosion of the natural creek area running through their neighborhood.
o To this point, City staff has done the following:
§ Because they were flooding hazards, in July staff removed the stump of a fallen tree from the creek behind 219 Westpark Drive South and removed woody debris that had collected behind 109 Poppy Lane.
§ To protect the existing sanitary sewer aerial crossing behind 110 Poppy Lane, the City’s drainage team on August 4, 2016, added additional rock riprap near the base of the columns holding up this aerial sewer line.
§ Based on the recommendation of the City’s Landscape Architect, this month crews removed four trees from the creek. Three were clumped together behind 219 Westpark Drive South and one was behind 217 Westpark Drive South. No further trees are recommended for removal at this time.
o Staff also recommends to soon do the following:
1. Make improvements to the existing stepped concrete retaining wall structure located behind 114 Poppy Lane and 112 Poppy Lane to address scour that is threatening the structure. This work will also provide some erosion protection to upstream properties. ($30,000)
2. Install energy dissipators and riprap to the existing 54” storm sewer outfall at the upstream end of the ravine behind 219 Westpark Drive South and 115 Poppy Lane to reduce erosion in the vicinity of the headwall. ($20,000)
The two items shown above are in compliance with the revised City policy. Anything beyond that may warrant a revision to the policy.
o Other potential mitigation options include:
3. Additional grade control structures ($40,000)
4. Erosion protection of channel banks at the “hairpin” turns ($400,000)
5. Creating a natural floodplain bench ($850,000)
6. Diverting higher flows directly to Jean’s Creek ($900,000)
7. Piping runoff through the ravine ($900,000 or up to $2,900,000 if mitigation is required)
8. Protecting the channel banks of the entire ravine ($1,400,000 or up to $3,890,000 if mitigation is required)
In addition to the above recommended steps #1 & #2, staff recommends that the City Council consider approving an exception to the policy to include Option #3, the additional grade control structures ($40,000), as it will provide additional protection of the City’s existing infrastructure and mitigate erosion.
FINANCIAL SUMMARY:
• The Surface Drainage Utility System (SDUS) fee provides funding to address a certain amount of drainage concerns each year. No changes in funding are anticipated due to the adoption of this revised policy.
• Regarding Westwood Park:
o The recommended improvements to the existing stepped concrete retaining wall structure and the storm sewer outfall may cost up to $90,000.
o Additional mitigation options vary in cost from $40,000 up to $3,890,000.
o Funding may be available from the SDUS fee and the Capital Improvement Program. Funding toward this issue will reduce funding available for other outstanding drainage tasks.
BOARD OR COMMISSION RECOMMENDATION:
• N/A