Is Colorado’s Massive Dam Expansion in Trouble?

Quick Overview

The expansion of Colorado's Gross Reservoir faced a temporary halt in April 2025 due to a federal judge ruling that Denver Water's permitting process violated the Clean Water Act, citing extensive and serious deficiencies, though construction was later allowed to continue.

Key Points: The Gross Reservoir expansion project, aimed at increasing storage capacity for Denver and Boulder County, was temporarily stopped by a federal judge's injunction in April 2025. The judge faulted the U.S. Army Corps of Engineers for permitting construction without fairly considering alternatives to dredging and filling 'waters of the United States,' specifically South Boulder Creek. The original 1950s gravity dam is being transformed into a larger roller-compacted concrete (RCC) dam, raising the structure by 131 feet to increase capacity from 33,404 acre-feet to 119,000 acre-feet (or 150 million cubic meters). Environmental groups, including Waterkeeper Alliance and Sierra Club, successfully argued that the Corps failed to adequately analyze climate change impacts on precipitation, which affects future water availability. Denver Water announced in 2020 that it was already serving 1.5 million daily users, a figure projected to continue growing. The construction method involves laying Roller Compacted Concrete (RCC) in 4-foot lifts, which requires lower curing temperatures and reduces the risk of cracking compared to traditional concrete. Despite the temporary setback, Denver Water appealed, and a later ruling allowed construction to resume, with the dam expected to top out in 2026 and be completed in 2027.

Context: The video discusses the controversial expansion of the Gross Reservoir in Colorado, which is crucial for supplying water to the growing Denver metropolitan area and Boulder County. The project involves raising the existing 1950s gravity dam into a much larger roller-compacted concrete (RCC) dam to increase storage capacity, a necessary step given increasing regional demand and ongoing drought conditions. However, the project faced significant legal challenges from environmental groups arguing the expansion would harm local ecosystems, particularly South Boulder Creek.