It had been raining pretty hard that night in Boulder, Colorado, harder than normal for a place that is arid, has as many days of sunlight as Los Angeles, and by some accounts is considered a desert (we have cacti). I'm a weather geek, so I get pretty excited whenever it rains, but I was not particularly concerned. I went to sleep that night like normal.
At 6 a.m., my husband woke me up and said, "the basement is flooded." After about 10 seconds of muttering angry words, I got out of bed and went to look for myself. Our house has a unique design: we have a type of split-level house where there is a lower level that has two bedrooms halfway below ground, then you go down another flight of stairs to the basement that is completely below ground. Well, the lower level bedrooms are all carpet, and they were completely soaked. Worse yet, the basement (which luckily was tile) had about 2 inches of standing water in it. We use our basement for storage, and we move houses so frequently that despite living there for over a year, most of the stuff was still in moving boxes that I had not bothered to unpack.
Despite the fact that it was the beginning of September, I went out to the garage and got my snow boots with rubber soles. Why would I own any other rubber boots in the desert? I started tossing everything I could onto shelves, furniture, the washer and dryer, and the rest on the stairs where my husband sprinted to all areas of the house, putting things anywhere there was a dry spot. The living room, the dining room, the master bedroom, the kitchen, the bathrooms. For 2 hours we frantically ferried all that we could out of the basement.
Then there was the carpet in the lower bedrooms. We put every towel we had on the floor to try to soak up the water, but it barely had any effect. By this time, it was not raining hard anymore, though it was cloudy outside. Afraid to run the drier in case there was any kind of electrical risk from the water in the basement, I laid the towels out on the driveway to give them a shot at drying. The neighbors were all outside, and we shared stories about how everyone's house on our block had flooded. As luck would have it, the rain returned, lighter this time, but undoing any progress of drying the towels.
Boulder, and cities east, lie in a flat plain, with the Rocky Mountains rising sharply at the west edge of town. Rain had also been falling in the foothills. The city now had a second problem: all that rain that had been falling at higher altitudes was now rushing down through all of the rivers and creeks that flow down to the plains. Boulder is designed for flash floods of this sort with many drainage ditches to move water east of town, but these drainage ditches were not equiped to handle this magnitude of water flow. By nightfall, the Boulder Creek, the main waterway that flows through downtown had completely overflowed its banks.
The civil defense sirens sounded. My house is two miles from the creek and sits on a ridge, so we were not in immediate danger. Since the temperature was mild, all the windows in the house were open. I remember hearing the eerie sirens in the distance, along with a loud speaker ordering people to evacuate the area near the creek. Even a few inches of swiftly moving water is enough to knock a person over. I grew up in Illinois, where there are tornadoes, and civil defense sirens are common place (we, stupidly, would usually just run outside to look or just shrug with apathy). But, other than monthly tests, this was the first an only time I have heard them in Boulder, now even as a seven year resident. And I'd certainly never experienced a flood in my life.
Now colloquially referred to as "The 2013 Floods," on September 9, 2013 a weather system stalled over Colorado and brought heavy rains. Initially, 7 inches of rain fell in 6 hours. Because the region had been experiencing a drought, the ground was not able to efficiently soak up the water. By September 15, 17 inches of rain had fallen, which is just below Boulder's annual rainfall total of 20.7 inches. Boulder Creek, which runs through downtown Boulder, regularly flows around 150–200 cubic feet per second, and by September 12th was flowing at over 5000 cubic feet per second. Prior to the flooding event, the National Weather Service had issued adequate flood and flash flood warnings, but the enormous volume of water and the fact that it was an unusual time of year for heavy precipitation caught many off guard.
Roads from Golden, CO to Lyons, CO that lead into the foothills of the Front Range washed out and were completely impassible. Contact was briefly lost with some smaller communities in the foothills, such as Ward, CO, that had no power, no phone, and no cellular service. The town of Estes Park, CO (famous for sitting at the east entrance to Rocky Mountain National Park) was completely unreachable by road, and along with other towns, supplies had to be delivered by helicopter from the National Guard. Lyons, CO, sitting at the base of the foothills on the St. Vrain River experienced extensive damage. Many homes were filled with 1-2 feet of sand that had been deposited by the river and were a complete loss. Throughout the area, nearly 19,000 homes were damaged, and over 1,500 were destroyed. At least 1,750 people and 300 pets were evacuated by air (mainly by helicopter). The governor of Colorado declared a state of emergency for 14 counties, followed up later by a federal declaration. By the end of the disaster, there were eight deaths and six people determined missing.
The 2013 flood is still fresh in the mind of many Boulder residents. Whenever it rains for more than a few minutes, both my husband and I get a little bit nervous in the back of our minds. If someone's sump pump comes on, there is always a panicked email on our neighborhood email list. Boulder is home to the University of Colorado Boulder, and as a college town has many renters, including myself. The City of Boulder Open Data Catalog provides data of the addresses of the city's rental properties as well as geographic data of the extent of the 2013 flood and the county's floodplains. An app that lets renters and property managers know if the property they currently rent or are considering renting lies in a floodplain is a useful tool given recent community events.
Rivers and creeks naturally experience small flooding events, and their paths meander slightly. The flat, low-lying area near the normal course of a river is called the floodplain. These minor floods deposit silt, sand, and nutrients to the floodplain, which in rural and agricultural areas can be a vital source of materials that make the land in the floodplain fertile. However, many cities are built on rivers for their water resources, and flooding in these cases is not desirable and leads to damage to infrastructure.
In this app, you will see terms like '100 year flood' or '500 year flood.' These terms represent the probability that a flood will occur. For example, a 100 year flood means there is a 1 in 100 chance (1%) chance of a flood occurring. Assuming the weather each year does not depend on the previous year, it does not mean that just because a flood occurred in 2013 that Boulder is safe from another catastrophic flood for then next 100 years!
You can find a link to the source code on my Github page here.