You are here

Frequently Asked Questions

The City updated its impervious cover and property data that the drainage charge is based on. The City is now using 2015 aerial imagery, current building permit data and current appraisal district data. In general, changes to the charge were more likely if one of the following is true:

  • You added a patio, deck, driveway, parking, shed, addition or other improvement between 2012 and 2015.
  • Your address has a lot of trees. The new data better reflects impervious cover hidden by the tree canopy.
  • Your address was developed between 2012 and 2015. In this case, the previous drainage charge was based on either building permit data or unimproved conditions. It is now based on aerial imagery.
  • You store vehicles, rock, dirt or other materials on unpaved areas. These open storage areas are considered impervious cover. The new data contains more of these open storage areas than the previous data.
  • Your address was subdivided or merged with another address since 2015.

The Watershed Protection Department is in the process of developing a Stormwater Management Discount for both residential and commercial properties. The discount would be for stormwater controls that exceed the legal requirements for development. Find out more about the proposed discount program.

In addition, if you have an uncovered wooden deck and an unpaved portion of your driveways, we may be able to lower your impervious cover, which will in turn lower your bill. If you have these features, please call 512-494-9400 and ask about an administrative review of your drainage charge.

From October 2015 to October 2016, residents in single-family homes received a discount if their charge was above $9.80. This discount was meant to help phase in revisions to the drainage charge and expired in October 2016. There's more information on the single-family discount web page.

The following groups are exempt from the drainage charge:

  • The state
  • Counties
  • Independent school districts
  • Universities
  • Religious organizations that participates in a specific program to provide housing for the homeless.

In addition, the charge does not apply to properties outside the city limits and properties that have not been developed.

Residential customers may request a reduced drainage charge based on financial need through the Customer Assistance Program. This discount on the drainage charge is only available to those being billed directly by the City for drainage. It is not available to residents of multifamily dwellings for which the property owner or owner’s agent pays the drainage charge.

If you rent a single-family home, duplex, triplex, fourplex or garage apartment, you will be charged for drainage on your electric bill. When there are multiple units, such as a duplex, we divide the charge evenly among the units.

If you rent an apartment in a complex with more than four units, we will charge the property owner or manager for the whole property. They may choose to allocate the charge to their tenants keeping in mind any applicable provisions in the lease agreement as well as the requirements in City Code Chapter 15-9 (Utility Service Regulations).

In general, the answer is yes. Stormwater runoff generated by impervious cover continues to occur whether or not the property is vacant. In addition, the City is striving to keep uncollected fees from vacant properties to a minimum to keep the rates as low as possible for everyone.

The process is different depending on whether the owner or the tenant(s) are paying for utility services. Tenants may be paying for utilities in single-family residences, duplexes, triplexes, fourplexes and some commercial properties.

If the owner of the property is paying for utilities, and shuts utilities off for vacancy reasons, the drainage charge will remain as a charge to that owner.

If tenants on a property are paying the drainage charge and call to shut down their utility account, then the charge will be transferred to the owner of the property, whenever possible. There may be situations where the property is vacant for only a short period of time and we are not able to bill the owner in the limited time.

City Code section 15-2-12 and City Code Chapter 15-9 Article 12 provide a process for requesting a review of your drainage charge and for adjusting your drainage charge, if warranted. The process includes an administrative review by the Director of the Watershed Protection Department and an administrative hearing by a hearings officer. There is more information about this process on the Drainage Charge Administrative Review web page.

Please call 512-494-9400 to initiate your request for administrative review.

The adjustment factor is based on the percent of impervious cover on an individual property. It adjusts the drainage charge upwards for properties with more than 52.3% impervious cover and downwards for those with less than 52.3% impervious cover.

It is calculated for each property using this formula:

Adjustment Factor = (1.5425 x percent impervious cover) + 0.1933

The formula for the adjustment factor is based on the “weighted” average percent of impervious cover for the entire city, currently estimated at 52.3%. A weighted average is a more accurate way to calculate an average when the items being averaged are of relative importance to each other.

The City of Austin will calculate your drainage based on the following formula:

Monthly Drainage Charge = Monthly Base Rate x Impervious Cover x Adjustment Factor

Monthly Base Rate

The monthly base rate for Fiscal Year 2016 to 2017 is $0.00498 per square foot of impervious cover. This represents a slight decrease from the previous fiscal year.

Impervious Cover

The impervious cover for each property includes surfaces like rooftops, driveways, parking lots, walkways and patios. The City has measured the impervious cover for each property through its aerial data and mapping software, supplemented with zoning and development records.

Adjustment Factor

The adjustment factor is unique to each property and is based on the percent of impervious cover. It is calculated with the following formula:

Adjustment Factor = (1.5425 x Percent of Impervious Cover) + 0.1933

 

Drainage is “stormwater” that does not soak into the ground. It refers to water that falls as rain and runs off the land, and especially off of pavement or structures placed on the land. The City’s drainage system handles this water, and it consists of pipes, inlets, culverts, street gutters, ditches, channels, creeks, lakes, ponds, dams, tunnels and floodwalls.

Drainage can be a problem because of flooding, erosion and impacts on water quality. The drainage charge pays for programs that prevent, mitigate and/or correct these problems.

The drainage system should not be confused with the sanitary sewage system, which takes away water used in homes, businesses and industries for toilets, sinks, showers, washing machines and various types of business processes. The sanitary sewer system is a different system of pipes and infrastructure that lead to a wastewater treatment plant.

The stormwater drainage charge is shown on your monthly utility bill in the Drainage Service section. It funds the City of Austin's drainage utility mission and is authorized by the Texas Local Government Code.

The drainage charge was first adopted in 1982, the year after the 1981 Memorial Day Flood, which killed 13 people and caused $35.5 million in damage.

The drainage charge pays for a wide variety of programs to help with flooding, erosion and water pollution across Austin. Many projects and programs are working quietly behind the scenes to protect lives, property and the environment. Crews clean trash and debris from Lady Bird Lake, maintain our drainage infrastructure, and respond to more than 3,000 service requests annually. Staff respond to the pollution hotline about environmental spills and emergencies 24-hours a day. They coordinate numerous projects to help reduce the risk of flooding and erosion. Many of the programs, services and projects listed on the Watershed Protection Department web site are funded in whole or in part by the drainage charge and would not be possible without the charge.

Some projects that are funded entirely or in part by the drainage charge include:

  • ATXfloods and closing of flooded low water crossings
  • Restoration of the Shoal Creek Peninsula along Lady Bird Lake
  • Boggy Creek Greenbelt Streambank Restoration
  • Combating hydrilla on Lake Austin
  • Buyouts of flood-prone properties

The rate structure for the drainage charge is based on the impact that buildings and other improvements on a property have on Austin’s drainage system. It is important to note that the charge is based on the impact to drainage by manmade structures, not naturally-occurring drainage. State Code only allows municipalities to charge properties that have a structure or other improvement on it. Undeveloped properties are exempt from a charge.

The City is using both the amount and the percent of impervious cover on each property to calculate the charge because using both these parameters provide a very accurate basis for determining the proportional impact of each property to the drainage system.

The City completed a Stormwater Runoff Study in 2008. During the more than two decades of this study, staff collected measurements for 36 monitoring stations citywide. The study indicated that higher percentages of impervious cover result in higher stormwater runoff volume. Stormwater runoff contributes to flooding, erosion, and water pollution.

The City also uses standard hydrologic methods to design drainage improvements like storm sewers or creek bank stabilizations. These standard methods drive our construction costs and also closely relate to the observations from the 2008 Stormwater Runoff Study. Both standard methods and local observation indicate a strong correlation between runoff volume caused by development through the amount and the percentage of impervious cover.

Using both the percent and amount of impervious cover to calculate the charge provides a way to more closely relate the drainage charge to the individual impact of each property’s development to the operations and maintenance of the City’s drainage system.

There are several ways to estimate impervious cover citywide. For most properties, we are using aerial photography and LIDAR data obtained in 2012. For properties developed or modified afterwards, we need other sources of information. Originally, we based impervious cover estimates on:

  1. Construction site plans and building permits
  2. The impervious cover values already in use for assessing the drainage charge

Of these options, the first is most reliable. We are gradually converting impervious cover estimates to construction site plan and building permit data for properties developed after 2012. Account holders may see a change in their drainage charge as these updates are made. In the vast majority of cases, the changes to the drainage charge have been less than $10 per month.

The impervious cover data was generated using two different aerial photography and LiDAR data, collected in January 2012. The data was used to create impervious cover maps seen on the Find My Drainage Charge Map Tool. (For best results, use Internet Explorer 9 or higher, Firefox, Google Chrome or Safari.)

Aerial Photography

Each pixel on the aerial photography represents 6 inches on the ground. The accuracy is suitable for defining the edges of buildings, patios, driveways and other types of impervious cover.

LiDAR

LiDAR is a remote sensing technology that measures distance by sweeping a laser rapidly across the ground from the bottom of a plane flying low over the earth. The reflected light is gathered as a cloud of three-dimensional points and measured to determine how much light is reflected. Different surface types return a different signature of light. How long it takes the light to reflect from objects on the ground can indicate the height of these objects. LiDAR helped define impervious cover under tree canopies and the edges of buildings.

Updating the Data

Aerial photography for 2015 has already been taken, and a project is currently underway to update the 2012 impervious cover to match the 2015 photography.
 

If you make changes to impervious cover on your property, expect your drainage charge to change. However, there may be a lag time before changes are reflected in your charge. Changes that may affect your charge include increasing your parking, building an addition or adding a deck or shed. Removing impervious cover will reduce your charge. If you have removed impervious cover, please call 512-494-9400 to let us know, so we can adjust your charge for you sooner.

If you want an estimate of how changes to your property will affect your drainage charge, use the Drainage Charge Estimator.

Impervious cover is any type of human-made surface that doesn’t absorb rainfall, including:

  • Rooftops
  • Patios
  • Driveways
  • Sidewalks
  • Roadways
  • Parking lots
  • Some decks

Uncovered wooden decks and unpaved portions of driveways count as 50% impervious cover. If you have these features, we may be able to lower the impervious cover on your account, which will in turn lower your bill. Please call 512-494-9400 and ask about an administrative review of your drainage charge.

A more complete definition of impervious cover is found in Section 25-8-63 of the Austin City Code.

 

Information may not be available because the account holder has requested confidentiality. Under the Texas Utilities Code, customers have a right to confidentiality in government-operated utilities. A customer can request that their address, phone number, billing information and information related to their volume of utility usage be kept confidential. For more information, please visit the Austin Energy web page explaining Confidentiality and Customer Rights.

Alternatively, impervious cover may not be shown if the property was developed after January 2012, when aerial photography and LiDAR data was collected. This data was used to create the maps shown on the "Find My Drainage Charge" tool.