Flooding

Front Range has lessons for local rivers

Like many others who live in the mountain West, Southwest Colorado residents surely have been horrified by photos and video of flooding on the northern Front Range.

The floodwaters have destroyed roads and buildings, swept away cars and killed people. Receding, they will leave tremendous piles of debris, and the water that is now flowing down the Platte toward the Missouri River, the Mississippi and the Gulf of Mexico, is carrying pollutants that are dangerous for crops, fish and humans.

At least four people are dead and many more are missing. The Denver Post has reported that thousands are homeless, and the cost of the damage will be well into the billions. Taxpayers will pay a substantial part of that bill, and rescue workers have risked their own lives to save others and to prevent even worse damage.

The disaster offers a lesson relevant for regional rivers including the Animas, Pine and the Dolores River Valley above McPhee Reservoir.

The Dolores likely will not experience a flood of that magnitude, because its watershed is not that vast, and because such catastrophic rains are even less common in Southwest Colorado than they are in the northern part of the state.

But someday, these rivers will flood again, and it will sweep debris down their respective valleys, through the towns of Durango, Bayfield, Dolores and into McPhee Reservoir, which supplies water for agriculture and for drinking. The amount and kinds of development up the river in each of these cases will help determine the degree of damage downstream.

No one is suggesting that development be prohibited. It is impossible to limit human habitation to places that are guaranteed never to flood, burn, be buried under crushing snow or experience winds that can destroy anything constructed in their path. Nature always can win, and geology certainly demonstrates that nothing is safe forever.

But it is possible to calculate risk with a fairly high degree of accuracy. In the case of flooding, the more distance and elevation that separate a structure from a stream, the less likely the stream is to destroy it.

The span of records in the Rocky Mountain West is short even in human terms, but statistics can show how often and how high the river has risen over that time. With that information, it’s possible to draw parallel lines that predict degrees of risk. Anything built 5 feet from the river as it flows in September will be gone by next spring. Another, farther distance, provides more safety, along with less risk of contributing to damage downriver.

That is the purpose of setbacks, and it is logical. They are not guarantees – this week’s flooding leaves no doubt about that – but data-driven predictors of the likelihood of destruction.

Those who remember the horrific Thompson Canyon disaster of 1976 cannot be surprised at the destruction there in 2013. That is not true everywhere, but some of the destruction now being shown on television has occurred in places where the risk was well-known.

Historical photos show what the Dolores has done just in the years since photography came to the Dolores Valley. It makes absolute sense to draw a line, whether it be 100 feet or another distance logically chosen, and push construction behind it.

Water does not stop at property lines, which makes what people do in the flood plain the business of everyone downstream, as well as taxpayers and insurance customers everywhere. Setbacks are more than a property-rights issue. The pictures from northern Colorado have demonstrated that very clearly, and county commissioners throughout the region must pay attention.