What can the Arkansas River basin learn from flooding in Northern Colorado in September?
Some impacts of the historic floods on ditches will take years to sort out, said Sean Cronin, executive director of the St. Vrain and Left Hand Water Conservancy District in Longmont. He spoke at an American Ground Water Trust conference last week. More than half of the 95 ditches and reservoirs within the district reported damage from the flood.
Damage totals are still unknown, but could easily absorb the $2.3 million in grants and $40 million in loans made available by the Colorado Water Conservation Board. Many ditches already have made quick repairs, but some reservoirs and diversions could take years to repair. In some cases streams shifted from their historic channels.
“We got the message out early that nobody’s riding in on a white horse,” Cronin said. “We told our ditch companies ‘you need to do this.’ ”
The district is helping ditch companies navigate through processes to obtain permits or relief through state and federal agencies.
While Cronin described the impacts on areas in Boulder County, implications for the Arkansas River basin could be gleaned from his presentation.
Before the flood
Numerous small gravel-pit reservoirs are in the St. Vrain River watershed between Lyons and Longmont.
“They’re attractive because no permits are required, but they became unzipped from Lyons to Longmont,” Cronin said.
In the Arkansas River basin, a series of small retention ponds has been suggested as a way to reduce peak flows from a large,100-year flood on Fountain Creek, the Arkansas River’s largest tributary. The last 100-year flood on Fountain Creek occurred in 1965, but would be much heavier now because of growth in Colorado Springs. A demonstration pond in Pueblo, similar to the type proposed, suffered some damage to its outer wall from a much smaller flood during September. A U.S. Geological Survey study shows that 10 ponds between Colorado Springs and Pueblo would reduce the peak flow by 47.7 percent, but would have little impact on huge loads of sediment that would be expected in a 100-year flood.
During the flood
There was some capacity in ditches in the St. Vrain watershed to redirect some of the flows as flooding occurred, until reservoirs in the system were completely overwhelmed during five days of rain.
During the same period, in the Arkansas Basin, ditches in the La Junta area cooperatively moved water from a “wave” from El Paso County that migrated down Fountain Creek and into the Arkansas River. Coupled with tamarisk removal from the river channel through La Junta, the peak was reduced to avoid the type of damage North La Junta incurred during 1999 floods.
The historic 1965 Fountain Creek flood in the Arkansas River basin caused $37.5 million in damage, much of it to cities and farms east of Pueblo, as well as Pueblo’s East Side.
Diverting some of the water on Fountain Creek, either to Chico Creek or to an off-channel reservoir, has been suggested and modeled in the USGS study. The alternative would not be as effective as either a large dam or a series of smaller ponds.
After the flood
Protection of junior water rights often is mentioned during discussion of detention of water on Fountain Creek.
After the September flooding in the South Platte basin, the Colorado Division of Water Resources measured the impact of groundwater interception of increased flows during the flood. While groundwater levels rose rapidly during flooding, they decreased quickly as the river level dropped. The net gain to the system after the majority of water rushed past was about 7.8 percent.
“The question comes up, ‘does that erase the depletions from past well pumping?’ ” said Kevin Rein, deputy state engineer.
The state’s answer was “no.” The additional water was not allocated to junior water rights, but divvied up through the same priority system that satisfies senior rights first.
Of course the most devastating impact of a flood is damage to infrastructure. The state has reconstructed the roads destroyed by the September flooding on a temporary basis, and it will be years before they are completely rebuilt. For ditch companies, the questions of rebuilding become more complicated and problematic.
While any ditch would welcome more water, September’s flooding leaves the question, “What if it comes at the wrong time?”