Denver streets are a critical and necessary part of the drainage network. During large rain storms, the streets work together with the underground pipes to carry stormwater to the creeks and gulches. Denver standards allow for surface flows in excess of the pipe capacity to be carried by the streets at one-foot of depth or less during heavy rain storms. Streets that experience more than one foot of depth likely need a larger underground system than what currently exists. Identification of these undersized neighborhood pipe systems can be found in the Denver Storm Drainage Master Plan.
Many of the older systems in Denver were not constructed to handle the type of density and amount of imperviousness that is seen today. The average age of Denver’s storm drains is 39 years, with some of the oldest pipes 90 years old or more. As more land is developed in these areas, the increase in water runoff from added impervious surfaces can overwhelm the capacity of the older systems. In the newer parts of town (i.e. Green Valley Ranch, Stapleton), the systems were constructed with a higher level of service that meets today’s industry standard.
Public Works' Wastewater Management Division Systems Maintenance cleans storm drains on a regular basis. There are tens of thousands of storm drain inlets citywide, so not every drain is cleaned after every storm. If you suspect that a storm drain or storm drain inlet is clogged, please call Wastewater Operations 303-446-3658.
Yes, homeowners can do a lot, including:
The Storm Capital Improvement Program (CIP) needs to be expanded in order to mitigate flooding issues throughout the City, remove properties from regulatory floodplains, address significant flooding locations, improve water quality and improve public health and safety. The rates need to increase as construction costs in the aftermath of the Great Recession have risen faster than anticipated four years ago.
Flood insurance policies are approximately $400/year for single family residents and $1000/year for commercial industrial properties. Congress has mandated FEMA go to actuarial based rates, which will result in significantly increased flood insurance premiums. Many in our community cannot afford the current rate. Importantly, flood insurance covers limited losses after a flood, but does nothing to prevent flood damage.
Only robust funding of a storm drainage capital improvement program will reduce flood risk, prevent damage, and enable properties to reduce dependency on increased flood insurance policies.
The General Storm program is an annual program consisting on average of three to five smaller-scale, complaint driven projects that address local neighborhood flooding and/or maintenance issues. Incoming complaints that meet the minimum drainage criteria for a storm drain are documented and tracked by WMD staff. Criteria such as (1) reoccurrence of issue, (2) risk of property damage, (3) reduction to maintenance, (4) cost share opportunities, etc. are used to objectively defined which projects are chosen for that particular year. Projects are packaged together and bid as one to take advantage of more highly qualified contractors and on-average, lower unit bid pricing.
Flooding can affect any property. Some ways that the City highlights areas that have a potential to flood are through FEMA floodplains, Potential Inundation Areas (PIAs), and Significant Flooding Locations.
FEMA identifies 100-year floodplains along open waterways, creeks, gulches and rivers where owners with a federally backed loan are required to pay flood insurance; these areas are known as FEMA floodplains.
Additional information on floodplains:
Similarly, several of Denver’s low-lying streets, and many of the urban areas of the City, not adjacent to open waterways are susceptible to excessive runoff during heavy rains. These areas are considered Potential Inundation Areas (PIAs). The city is in the process of identifying these lesser known PIAs to help owners adequately protect their assets. PIAs are not FEMA floodplains and flood insurance is not required in PIAs; it is optional at the discretion of the property owner. Property owners in PIAs are encouraged to implement floodproofing measures (see the City and County of Denver Flood Protection Handbook PDF) and explore the need for flood insurance since flood damages are not covered by a typical homeowner policy.
Information and mapping of known PIAs can be found in the Denver Storm Drainage Master Plan.
Finally, the city highlights areas with reports of signification flooding and/or property damage with Signification Flooding Locations. These locations are labeled with Red Stars in the City’s Storm Drainage Master Plan. They do not reflect all reports received, only the most severe.
Information and mapping of known Significant Flooding Locations can be found in the Denver Storm Drainage Master Plan.
The best course of action to report a drainage problem is to call 3-1-1 and report the specific type of problem (i.e. ponding, flooding, icing, illicit discharge, broken inlet, blown manhole cover, etc.) and the location to the 3-1-1 operator who can best facilitate the request to the appropriate department for response.
Several hundred storm drains in Denver are siphons. Unlike a storm drain that carries flow to a river or gulch, a siphon merely conveys flow from one side of the street to the other where it bubbles up and continues flowing down the gutter. As shown in the diagram below, the water flows well during storms to get under the street and bubble back out on the other side. However, after storms whatever water is left in them sits and can get stagnant and start to smell.
Typical Siphon Drain (Illustration courtesy of City of Richland, Washington – Public Works Department)
Public Works-Wastewater Management Division Systems Maintenance cleans siphons on a regular basis in the spring, summer and fall and also puts in an EPA-approved larvacide tablet which lasts up to 30 days to kill mosquito larvae. Sometimes siphons get stinky between cleaning, especially during dry spells due to grass clippings, leaves, other organic matter which fall or are placed in the street and then wash into the siphon where they become trapped and start to decay. When this occurs the siphons need to be cleaned more frequently. In such cases, our Systems Maintenance staff can be dispatched to the site on their way out to their routine route, or on their way back to the office at the end of the day.
Each winter, the City and County of Denver receives calls regarding snow-plow operations and ice accumulation in the gutters along the streets. The Department of Public Works responds to these inquiries in several ways. While the Street Maintenance Division is directly responsible for snow and ice removal, these situations can also be an indication of other infrastructure issues, which involve internal cooperation and coordination with several Divisions within the Department of Public Works.
The Water Quality program provides a means to construct facilities to reduce pollutants in stormwater runoff and meet the current Total Maximum Daily Load (TMDL) for E. Coli that exists on the South Platte River and future regulations for nutrients. Water quality facilities, also known as Green Infrastructure, provide other citywide benefits including increased open space, heat island mitigation, improved air quality, and linkages for connectivity in urban corridors.
Green infrastructure has been found to reduce runoff for frequent events, but not for major runoff events. Stormwater professionals around the country are forming a consensus about the flood reduction benefits related to GI. In Colorado, the Association of State Floodplain Manager’s (ASFPM) Committee has sponsored a discussion paper on the topic. The conclusions of that paper are that GI is good to reduce flooding for frequent events, but not for large events such as 25-year, 50-year, or 100-year events.