To: Honorable Mayor and Members of Town Council
Through: David L. Corliss, Town Manager
From: Mark Marlowe, Director of Castle Rock Water
David Van Dellen, Assistant Director
Title
Ordinance Amending Section 15.36.010 of the Castle Rock Municipal Code for the Purpose of Adopting by Reference as a Primary Code the 2025 Castle Rock Storm Drainage Design and Technical Criteria Manual (Second Reading - Approved on First Reading on January 7, 2025 by a vote 7-0) [Castle Rock Boundary]
Body
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Executive Summary
The purpose of this memorandum is to seek Town Council approval of an Ordinance (Attachment A) amending Section 15.36.010 of the Castle Rock Municipal Code adopting by reference as a Primary Code the 2025 Castle Rock Storm Drainage Design and Technical Criteria (Drainage) Manual. The recommended changes to the Drainage Manual are primarily in response to issues that have arisen as a result of large storms more frequently impacting single family detached subdivisions over the last several years like the one which occurred on June 9, 2024. This strengthening of storms is a phenomenon being seen in many places, not just Castle Rock.
The Drainage Manual is a critical document governing the design and construction of new storm drainage infrastructure in the Town including storm sewer systems, street drainage, stormwater detention and stream channel improvements. The Manual is a key element in stormwater quality and floodplain regulations which the Town is responsible to implement based on state and federal regulations. Revisions to the Drainage Manual generally focus on 1) ensuring adequate street capacity in large storm events, 2) providing for additional inlets in residential subdivisions to address over icing of residential roads and reduce flow depths in smaller storm events and 3) ensuring designated emergency overflow paths for ponds and inlets (see Attachment B for a full list of proposed revisions).
There are no immediate direct cost impacts to the Town as a result of this action, however, these revisions will result in additional cost on residential development and increased public storm drainage infrastructure. The exact level of increase is widely varied depending on the circumstances; however, it is anticipated that the magnitude of storm sewer infrastructure could increase as much as double under these new criteria. Over the long term, the Town will have more infrastructure to maintain which will increase operational costs as a result of the proposed changes.
Staff Recommendation
Staff recommends approving an Ordinance to amend Section 15.36.010 of the Castle Rock Municipal Code adopting by reference as a Primary Code the 2025 Castle Rock Storm Drainage Design and Technical Criteria Manual.
Proposed Motion
“I move to approve the Resolution as introduced by title.”
Alternative Motions
“I move to approve the resolution as introduced by title, with the following conditions: (list conditions).
“I move to continue this item to the Town Council meeting on _____ date to allow additional time to (list information needed).”
Attachments
Staff Report
Attachment A: Ordinance
Exhibit 1: Redline version of Drainage Manual
Attachment B: Summary of Revisions