From the University of Colorado Denver
CU Denver study says upgrading infrastructure could reduce flood damage
DENVER (Oct. 29, 2014) – The severe flooding that devastated a wide swath of Colorado last year might have been less destructive if the bridges, roads and other infrastructure had been upgraded or modernized, according to a new study from the University of Colorado Denver.
“People need to understand the importance and seriousness of infrastructure,” said Jimmy Kim, PhD, associate professor of structural engineering at the CU Denver College of Engineering and Applied Science and lead author the study. “There is an assumption that a bridge will stand forever and that’s simply not true.”
Kim along with co-authors Wesley Marshall, PhD, PE and Indrani Pal, PhD, both assistant professors of civil engineering at CU Denver, the leading public research college in Denver, examined the causes of the flooding and its impact on infrastructure.
The stage was set for the deluge when an unusual low pressure system generated a steady plume of monsoonal moisture flow from the Pacific Ocean toward Colorado’s Front Range communities.
The rain began on Sept. 9, 2013 and didn’t stop until the 16th. In just days, places like Boulder County received three-quarters of its yearly precipitation. Bridges collapsed, roads failed and homes were swept away.
According to the study, 120 bridges now need structural repair. Many were damaged by rushing water which washed out backfill soil and exposed bridge foundations.
Kim said new `scour control’ methods, aimed at reducing these washouts, should be developed to help bridges withstand future flooding.
“You can do that by upgrading existing piers (columns) supporting the bridge or changing current design approaches” he said. “The Colorado Department of Transportation is currently working on improving scour design for bridge structures.”
The researchers also suggested improving roads made of concrete or bituminous material like asphalt since they often disintegrate when flooded. Kim said fiber, nano-particles or polymeric admixtures could be added to these construction materials to increase tensile strength and flexibility while reducing cracking.
The study noted the successful use of geographic information systems (GIS) to help supply up-to-the-minute mapping and alerts about flood damage.
“The production of such data and maps extended well beyond the typical GIS community and included local news affiliates and even the City of Boulder itself,” said study co-author Wesley Marshall.
For example, on September 27, 2013, Boulder launched a ‘Community Flood Assessment’ crowd-sourced map using the Crowdmap application. The city asked users to submit flood reports via the website or smartphone apps. They were also asked how deep the flooding was and if they lost power. Video and photos could be uploaded to locate the event on an interactive map.
“Such efforts were not only useful during the recovery efforts but will continue to be used toward helping increase the resiliency of Colorado during such events,” Marshall said.
Overall, the researchers revealed a much wider problem.
From 1980 to 2007, about 90 percent of all global disasters were caused by flooding either by rain, tsunami, hurricane or some other natural event.
At the same time, the American Society of Civil Engineer’s 2013 Report Card for America’s Infrastructure gave the country a dismal D+. The group said $3.6 trillion was needed by 2020 to address the most serious problems.
In Colorado, the report card says, 70 percent of major roads are poor or mediocre and 566 bridges are structurally deficient.
“Reconstruction is very expensive and should be the last resort,” Kim said. “But we can repair or strengthen existing systems less expensively. We are looking at a growing national problem, one that will only get worse if we ignore it.”
The study was published last week in the Proceedings of the Institution of Civil Engineers. It is available upon request.
From NOAA Sept 29th:
Climate change not to blame for 2013 Colorado floods
Heavy multi-day summer rain events not expected to increase in the area
Last September’s widespread flooding in northeast Colorado, which saw just over 17 inches of rain in one week in the city of Boulder, was not made more likely or more intense by the effects of human-induced climate change, according to a new NOAA-led study published today in the Bulletin of the American Meteorological Society. The Colorado research is part of an international special report on 2013 extreme weather events. NOAA’s media release describing highlights of the full report can be found online.
Colorado flood of 2013
“There’s clear evidence that overall, our greenhouse gas emissions are making the planet warmer and moister, but we found such climate factors had little appreciable effect on the frequency of heavy 5-day rainfall events in this area during September,” said Martin Hoerling, a research meteorologist at NOAA’s Earth System Research Laboratory in Boulder, Colorado, and lead author of the new study, which also included researchers from the Cooperative Institute for Research in Environmental Sciences (CIRES) and NASA. In fact, the study suggests that in this region, the likelihood of heavy rainfall events may have slightly decreased because of human-induced climate change.
Last summer’s extreme rainfall—17 inches is close to the city’s typical total for the entire year—was very unusual, but it wasn’t the first time Colorado experienced such heavy rains. Widespread flooding rains fell over the Front Range during several days in September 1938, before human-caused climate change was detectable. The two events were similar in many ways: they happened over a large area, lasted a long time, and were characterized by a slow-moving weather system that pulled lots of moisture into the region.
To tease out the impact of climate change on the 2013 floods, Hoerling and his colleagues used a climate model, developed by NASA, that contained detailed information on how various climate factors—such as greenhouse gas levels, ocean temperatures, and sea ice extent—have varied since the late 19th Century. Run many times, the model produced occasional heavy September rain events both at the end of the 19th Century (1870-1900) and in a recent 30-year period (1983-2012). Comparing those two time periods, the researchers found that the extra greenhouse gases, warmer oceans and lower amounts of sea ice of recent decades did not increase the likelihood of rains as heavy as those in September 2013.
Assessing flood impact
The researchers also explored what the future may hold for such rain events in this area, as greenhouse gases continue to rise. The team examined climate projections used in the Intergovernmental Panel on Climate Change (IPCC) assessments and found no significant changes in the risk of summer heavy 5-day rainfall events over the High Plains region, including Colorado.
Hoerling and colleagues stressed, however, that with further increases in water vapor in a warmer world, many parts of the world are likely to see more frequent episodes of very heavy rains. They said that what happens globally doesn’t necessarily explain what happens in one particular place, where local to regional processes may trump global ones. To figure out why that is, the researchers are doing further studies with other models.
If climate change didn’t cause the 2013 floods, then what did? “For this event, the weather pattern was much more important than climate change, or other climate factors such as ocean temperature variations and changes in Arctic sea ice,” Hoerling said. In this case, a slow-moving low pressure system pulled up moisture from the south and essentially stalled at the Front Range, dropping that moisture as heavy rains.
Authors of “Northeast Colorado Extreme Rains Interpreted in a Climate Change Context” include Martin Hoerling and Randall Dole from NOAA’s Earth System Research Laboratory; Klaus Wolter, Judith Perlwitz, Xiaowei Quan, Jon Eischeid, and Henry Diaz from CIRES; and Hailan Wang and Siegfried Schubert from NASA’s Goddard Space Flight Center.