What Have We Learned From the Flood?

What have we learned from the July 7, 2015 flood in Rock Springs?

First, the good news. The flood did not cause any loss of life or personal injury. In addition, the millions of dollars that the City spent on flood control over the past decade to construct various detention ponds south of town did make a positive difference. Unlike the 1989 flood, when Bunning Park was under water and property damage downtown was severe, this time property damage downtown was mostly limited to the labor of shoveling mud off the sidewalks and out of basements (mine included). City Director of Engineering Paul Kaucich deserves credit for promptly ordering a backhoe to remove debris from the grate at the large box culvert at D and Gobel streets on both July 6 and July 7. If he had not done that, downtown flooding would surely have been worse.

 

Also on the good news front, this flood event has raised awareness of weaknesses in the storm water drainage system. For example, for the residents and businesses along and east of Elk Street, the city is now coordinating with the U.S. Bureau of Land Management and the county to potentially construct an additional detention pond outside city limits east of Desert View elementary school to ameliorate the effects of the next heavy rain. Similarly, the city is starting to coordinate with WYDOT to fix the problems at the intersection of McCurtain street, Blair Avenue and the I-80 south side belt loop. Finally, the flood exposed problems at the confluence of Killpecker and Bitter Creek, where a sewer pipe that should be underground was partially exposed.

 

Box Culvert at D Street and Gobel

Box Culvert at D Street and Gobel

Now to the bad news. The box culvert at D and Gobel streets, where the water overtopped the levy on July 7, is a chokepoint of the downtown flood control system.  The city is poised to have the Utah engineers who designed the system evaluate their own design, which is like asking a teenager to grade his own English exam. If this outside engineering firm diagnoses the primary problem on July 7 as the city’s failure to properly maintain the system by clearing the ditches of debris, we will not have confidence that that is the full picture because of the inherent blindness anyone has in evaluating their own work. For example, a potential design issue is that the box culvert inlet at D and Gobel is about six feet tall (the water level was of course significantly higher during the event) but the outlet high water mark for a comparable stream width below F street appears never to have reached more than three feet.

Box Below

Culvert Outlet Below F Street

Did the water really flow twice as fast at the F street outlet or is there some other problem?

 

The other mixed picture is that the city in June just awarded a sole bidder contract for $4.3 million for storm water improvements, yet only a fraction of that money will go to address problems that the flood exposed.

 

What should we do? I am in favor of system modifications that have high benefits and low costs. Here are some suggestions: (1) Fill in the western edge of the detention pond above the horse corrals. A casual observer can tell that water overtopped the detention pond above the horse corrals on its western edge, which is strangely about two feet lower than the rest of the pond levy. This overflow likely contributed to the “wall of water” reported by the backhoe operator at D and Gobel on July 7 just before flood waters spilled onto D Street. Filling in that levy would appear to be a low cost way to mitigate the likelihood of overflow recurrence;

Detention pond

View of pond above horse corrals from western edge where overflow occurred

(2) work with the county, the BLM and the State to construct a detention pond east of Desert View elementary – this might be somewhat expensive but the benefits would be great; (3) develop a plan for ditch and culvert maintenance. For those ditches that are outside the city limits, coordinate with the county commission and the county sheriff . For example, of the average 130 inmates who stay at the sheriff’s hotel on 191, some could be tasked on a regular basis to remove tree branches and other debris without significant additional taxpayer cost; and (4) have the city’s flood control system reviewed by an engineering firm that did not design it. An unbiased review might reveal low cost design tweaks worth pursuing.

 

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