A brief history of the South Boulder Creek flood control fiasco

A brief history of the South Boulder Creek flood control fiasco
by Ben Binder

Years ago, both the City and County of Boulder followed the principles of McHarg and Gilbert White by choosing not to develop floodplains and wetlands, and instead, designating those areas for trails and open space.

That’s why the original reclamation plan for the 308-acre Flatiron Gravel Pit, located in the floodplain of South Boulder Creek, included large ponds and wetlands that would attenuate flooding and stated the site was going to be reclaimed as “habitat suitable for wildlife”.  That was the case until the depleted gravel pit was unloaded on CU.

Map of the South Boulder Creek 100-year floodplain in 1981 when Boulder County approved a gravel mining permit.

Removal of 4 million cubic yards of sand and gravel further lowered the topography 12 – 15 feet.

 

 

 

 

 

 

 

The Gravel Pit Reclamation Plan when CU purchased the property

The plan had ponds and wetlands that would attenuate flooding. The reclamation plan did NOT include a 6,000’ berm around the pit to divert floodwaters onto neighboring properties.  No one believed this plan could be rescinded.

But CU paid consultants to redesign the reclamation plan to maximize development in the floodplain by removing the ponds and adding a 6,000’ berm around the gravel pit to divert floodwaters onto neighboring properties.

 

 

 

 

 

 

 

 

 

 

 

Next, CU used its political power to lobby the state Mined Land Reclamation Board to adopt CU’s revised reclamation plan.

 

 

 

 

 

 

 

 

 

 

 

 

As a result, during the 2013 flood CU’s vacant gravel pit remained dry while neighbors were catastrophically flooded.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Next, CU held Boulder residents, whose homes were in danger of flooding, hostage for years and would not allow the city to use any of the gravel pit for flood control until the city agreed to annex the property and provide water and sewer utilities for future intensive development.  And that’s not all.

In 2001, CU developed the following Master Plan for the site.  It designated areas that would be developed and areas the city could use for flood control.  CU’s site plan was designed before floodwater detention plans were formulated, but it dictated the areas the city could use for flood detention.

When CU’s site plan was developed, floodwaters spilled out of South Boulder Creek and collected in the northern portion of the gravel pit near Table Mesa Drive.  Since that area would be underwater during a flood, CU considered the area undevelopable and hence designated it for flood control.  That’s why the city’s flood control plans include a three-story high-hazard dam along table mesa drive.

A less-expensive, safer, and more environmentally sound flood control plan would capture floodwaters near where they spill out of South Boulder Creek at the south end of the site, leaving the north end dry and suitable for development.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Below is the current South Boulder Creek flood control plan. Anyone knowledgeable about hydrology and floodplain management would cringe at the construction of a three-story high-hazard dam along Table Mesa Drive, the $19.4 million 2,600-foot-long concrete floodwall/spillway along US 36, excavated detention below the level of groundwater, and the $6.1 million outlet works tunneled under US 36 to drain the detention pond into Viele Channel.

The required detention volume could be accomplished with a far less expensive series of shallow ponds in the south end of the depleted gravel pit where they could drain directly back to South Bouder Creek before it flows under the US 36 Bridge.  This would eliminate the three-story dam, which must be crossed to access CU’s site, the $19.4 million 2,600-foot-long concrete spillway, excavated detention below the level of ground water, and tunneling under all six lanes of US36.

The city claims it studied such a plan and it would cost 50% more, but when I asked to see the study, they admitted such a study was never performed.

Boulder’s Current Plan for South Boulder Creek flood control

Note the South Loop Drive embankment needed to pass over the three-story dam.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In an April 7, 2021 email, former Colorado Dam Safety Chief Bill McCormick recommended that Boulder consider safer and far less expensive flood control plans using non-jurisdictional dams.  Boulder ignored that advice.

In a January 22, 2020 email to Boulder Project Manager Brandon Coleman, CDOT engineer Daniel Marcucci wrote:

“CDOT believes it is incumbent on Boulder to evaluate other options even if those options are not entirely desirable to the city.”

When the Boulder City Council first approved the project, CH2M Hill estimated it would cost $23 million, and engineering was estimated to cost $1.9 million.  To resolve problems with the plans, construction is now estimated to cost $63 million, $13 million has already been spent on engineering, and approximately $10 million will be spent on bond interest – a total of $86 million, an increase of nearly 400%.

This project is in dire need of an independent peer review before one penny is spent on construction.

Ben Binder PE, PLS, bbinder@ddginc.com