Arapahoe County moves to develop stormwater program for High Line Canal, board gives general approval to proceed

Arapahoe County officials outlined a multi-year plan to treat the High Line Canal as a managed stormwater asset and received general approval from the Board of County Commissioners to continue developing technical criteria, policy and implementation options.

The county’s Open Spaces director, Ginny Pangino, told commissioners the presentation was a high-level “50,000-foot” roadmap and asked for the board's concurrence to allow new stormwater discharges to the canal provided risks are minimized and benefits maximized. Pangino said staff aim to have the program defined enough to guide decisions by Jan. 1, 2027.

Why it matters: The county recently acquired 45 of the canal's 71 miles and faces choices about whether and how to accept stormwater that historically has drained into the channel. Allowing controlled stormwater could help sustain trees and the canal's vegetation and avoid the higher collective cost of redirecting flows to other municipal infrastructure, county staff and Denver Water said.

Denver Water's chief of operations and maintenance, Tom Rood, summarized the canal's history and earlier Denver Water policy of limiting stormwater. He said drought and changing irrigation practices over the past decade prompted new studies and regional cooperation. "If irrigation is gone, what's going to happen to the tree canopy?" Rood said, arguing that a coordinated approach could be more efficient than separate municipal projects.

Staff described a three-pillar program of (1) criteria & modeling, (2) policy and permitting rules, and (3) operations/implementation. The county's stormwater "stamp plan" (stormwater transition and management plan) uses lidar-based modeling to identify capacity limits, freeboard (the distance between water surface and top of berm), and overtopping risks. Staff cited model findings that about 80% of canal reaches have at least one foot of freeboard, 60% have two feet, and 35 locations were identified as vulnerable in a 100-year storm scenario.

Mile High Flood District and contractor ICON Engineering have offered to provide modeling and meeting facilitation: Mile High Flood District will host and financially support additional modeling under the stamp plan, and ICON will support criteria development, staff said.

What staff asked for: Pangino and county public works staff asked the board to concur in principle with three things: that (a) new stormwater discharges may be considered where technically justified, (b) the proposed framework (criteria, policy, implementation) should guide program development, and (c) Open Spaces together with Public Works should lead the development of policy and implementation workstreams.

Municipal partners that use portions of the canal urged clearly defined roles and a seat at the table. Cherry Hills Village said it had completed a local stormwater analysis and asked that municipalities be included in standards development; Greenwood Village and Centennial said they already perform maintenance and emphasized the need for consistent modeling so local projects do not cause downstream harm.

Commissioner concerns and operations: Commissioners pressed staff for clearer benefit-cost analysis and for assurances that permitting or fee structures would not make the program punitive for partners. Several municipalities and county staff stressed maintenance is expensive and emphasized debris removal, fallen tree management and consistency across jurisdictions as operational priorities.

Board response and next steps: After discussion, commissioners gave general, informal approval for staff to proceed with the framework and to use Mile High Flood District modeling and ICON support. A county staff action noted during the meeting directed staff to collect comments on the stamp plan, develop scope and criteria with ICON and Mile High Flood District, and return with recommendations on policy, permitting, and operations tied to budget timelines.

The county emphasized the work is preliminary: staff said the presentation provided a road map rather than firm policy and that implementation will require further modeling, stakeholder agreements and clarified permitting standards. The board asked staff to streamline review processes where possible so municipalities and applicants have a single point of contact for project intake.

The county will solicit formal comments to the stamp plan (the modeling document) and convene facilitated stakeholder meetings; staff indicated low-hanging operational actions (for example, reviewing whether certain head gates should remain open or closed) might be implemented sooner if they are technically warranted.

A formal ordinance or permitting code was not adopted at the meeting; commissioners asked staff to return with draft criteria, proposed implementation structure, and budget implications before final policy decisions.

Ending: The board's general thumbs-up sets staff on a pathway to draft the technical criteria and administrative framework; the next steps are comment collection on the stamp plan, facilitated stakeholder work with Mile High Flood District and ICON, and preparation of policy options timed to the county budget and implementation planning.