The biggest recorded event was in 1867, when the untamed river crested about 58 feet above normal levels, leaving most of Chattanooga underwater. Back then, catastrophic flooding that caused severe economic damage and mosquito-borne diseases occurred on a regular basis. In the early 1930s, when advocating for a system of dams and reservoirs to reduce the threat, the Tennessee Valley Authority (TVA) said Chattanooga faced more flood risk than any other location along the entire river. Nearly 100 years later, the 143.2mi² (370.8 km²) city remains focused on continually improving its flood resilience and our team has supported those efforts since 2012.
The Tennessee River is one of the most significant river systems in the U.S. and the largest tributary of the Ohio River. Passing through parts of seven states, it stretches 652 miles (1049.2 km²) and has a drainage basin that spans nearly 41,000 mi² (106,189.5 km²). While Chattanooga is largely protected by a series of 32 upstream dams and reservoirs that rank among the greatest irrigation and hydropower systems in the world, the city still has vulnerabilities. In addition to sitting on nearly 18 miles (28.9 km²) of riverfront, a series of local creeks and streams pass through low-lying suburban areas before feeding into the river. About 100 years ago, it was common for residential, commercial and industrial structures to be built in such locations. While regulations aimed at reducing or eliminating similar developments exist today, extant areas remain at risk.
Digitally Enabled Resiliency
In 2018, after our team had previously built hydrologic and hydraulic modeling of major watersheds for the city through an earlier Army Corps of Engineers program and helped them also obtain other methods of flow monitoring, Chattanooga reached out to us again, to find ways to leverage all that data – by creating the capability to recognize potential flooding threats in advance. The ultimate goal was to reduce the time needed to warn citizens of approaching danger. The precursor for this was the 1,000-year flood event that struck middle and west Tennessee, as well as parts of two other states, in May 2010. The widespread flash and river flooding, caused by two days of record rain, caught many communities by surprise, especially the city of Nashville. It was a wake-up call for Chattanooga, highlighting that, should anything similar happen there, they would need new, better and more effective ways to communicate flood risks to the 181K people who live in the city – especially during an ongoing flood event.
One of the custom-built tools we created for the city uses various inputs to predict, within a range, what magnitude of flooding could possibly be expected in specific locations within the next 6-to-24 hours. A key feature of our Chattanooga Flooding Level Calculator is its ability to leverage current rainfall data with flood elevation results from prior modeling. When combined with our algorithm, it’s able to calculate a range of predicted flood levels, by using real-time and forecast data inputs from the U.S. Geological Survey (USGS) and the National Weather Service (NWS). The benefits this tool holds for the city are immeasurable, because it provides city staff with essential decision-making support both before and during flood events - and that is key for any community, no matter how large or small.
Public Preparedness
Next, the city asked us to take it a step further and build a website that integrates the forecasts produced by the calculator and functions as a resource for the public who live or work in flood-prone areas, like South Chickamauga Creek, which is one of the major sources of flooding in Chattanooga. We created a Web-based Interactive Flood Viewer to display flood inundation boundaries and depths based on a wide variety of inputs such as current USGS levels, forecast data from the U.S. National Oceanic and Atmospheric Administration’s National Water Model (NWM), user defined flooding scenarios and the current NWS forecast. It can also use real-time radar images, as well as static base data from Chattanooga’s own GIS database. Visiting the online dashboard shows a series of gauges with the current flood stage. At the city’s request - we also included a scenario tab that shows users which areas and buildings could be affected by various levels of flooding.
The ability to have tools, like this, readily available in advance of and during flood emergencies also holds additional benefits for first responders and the wider emergency management community within Chattanooga and Greater Hamilton County. In fact, these tools hold relevance for every community that faces a risk of flooding.
Future-Focused Solutions
Our team differentiated itself by being one of the first to incorporate the national water model into the forecasting that populates our public-facing web tool. This project required a deeper understanding of flooding and its impacts across Chattanooga, as well as other factors like city operations and how communities will respond to flood information. It also required ingenuity, creativity and complex programming. The end-result is greater than the sum of the individual parts. Our team not only leveraged the city’s existing flood preparedness data, we created an essential foundation for innovative solutions that were both cost-effective for our client and transferrable to any other community in the United States.
