Record rainfall hit parts of Iowa for 12 straight hours in July 2010, sending 10 inches of rainwater draining toward Iowa’s Delhi Lake, a popular recreation destination for decades since its construction in the 1920s.
The 80-year-old Delhi Lake Dam, made of hundreds of feet of earth, concrete and steel, held back 9 miles of lake water with more rainfall flowing every minute. The water blew a 30-foot-wide hole in the dam wall, spewing floodwaters in the surrounding area.
State and emergency officials ordered early evacuations to prevent any loss of life. For safety professionals, the failure highlighted the threat posed to dams by climate change (increasing the risk of flooding), the importance of regular maintenance and inspection, and the impact of human error in dam construction on dam integrity.
In Iowa, there are a total of 95 high-risk dams. Up to 11.6% of these could pose a threat to residents, including those rated as an immediate threat or in poor condition, those not rated and those with no ratings.
As part of a national analysis, GetMyBoat identified the counties in Iowa with the most dams at risk of failure and the greatest potential threat to local residents, using data from the Army Corps of Engineers National Inventory of Damsretrieved October 2023. The public database that allows Americans to search the conditions of nearby dams has grown to include more than 90,000 dams.
As more dams are added to the national inventory, analyzes of this database reveal a increasing number of dams in poor and unsatisfactory conditionsome of which have the potential to be life-threatening if they fail—dams the reserve considers “high risk.”
Counties in this analysis are ranked by the share of high-risk dams that could pose a risk to human life, including those rated in “poor” or “unsatisfactory” condition, those that have not been inspected and those where the state agency that oversees them has not evaluated its terms. Links were broken by the total number of dams meeting these criteria and then by their concentration in local populations, although some links may remain.
A “poor” designation is given to inspected dams that exhibit deficiencies that threaten the integrity of the dam during normal operation. “Unsatisfactory” is given to dams that require “immediate or emergency remedial action,” according to the Army Corps of Engineers. About 1 in 10 of the dams listed in the directory have no status reported by government agencies.
“It is likely that most of these dams should be listed as unrated, but we will work with the relevant agencies to verify the information and update the NID accordingly,” Army Corps of Engineers spokesman Gene Paulik said in a statement.
Dam names accompanying each state in the analysis represent the largest dams in height that were in poor or unsatisfactory condition. The total number and concentration of high-risk dams gives a sense of the stakes associated with aging infrastructure in each state, though these figures do not factor into the rankings.
The dam of the Delhi Lake was reconstructed and made last inspection in 2020, receiving a “satisfactory” grade. The barrier is considered a risk level below high risk, “significant risk”. But its failure in 2010 exemplifies the high stakes facing communities living near large dams when they fail.
Illinois ranks high on this list, mostly because of the unknown conditions of its dams. The Army Corps of Engineers leaves it up to government agencies to decide what information it provides or withholds from the public database. Illinois only shares information on three of its dams that are considered high risk. One of her engineers has previously said she doesn’t assess dam conditions because the process is too resource-intensive to justify.
Many state and federal agencies have chosen to do so keep the data about these dams hidden, citing threats to national security. North Dakota and Oregon keep data on about 40 percent of the dams in their states, making it difficult for locals to gauge how many are in good shape or need attention.
Other states rank poorly for their share of high-risk dams that have gone uninspected. In Missouri, approximately 42% of these dams do not have a recorded date of last inspection. Another 24% were last inspected before 2000.
Read on to see how dams cost in your area based on publicly available data.
