What is Impervious Cover?
Per Chapter 16 of the Unified Development Code: Impervious Cover – Any hard-surfaced, man-made area that does not readily absorb or retain water, including, but not limited to, building roofs, parking and driveway areas, pavement, graveled areas, sidewalks, and paved recreation areas. Impervious Cover is subject to the determination of the Development Engineer. Includes and may be referred to as the term “Impervious Surface”.
Why is there Impervious Cover Limitations?
Per Chapter 11 of the Unified Development Code : Impervious cover limitations are adopted to minimize negative flooding effects from stormwater runoff and to control, minimize, and abate water pollution resulting from urban runoff of rainwater or other non-point specific sources, pursuant to Texas Water Code § 26.177
Is there a variance to Impervious Cover Limitations?
Only in unique circumstances.
Impervious cover limitations may be established when a property is subdivided (Subdivision Plat). In this case, a restriction is added to the Plat detailing the maximum impervious cover for the subdivision and per lot. If your Plat identifies the maximum impervious cover allowed, a variance may not be granted.
If no impervious cover limitation is established by the Plat, a variance may be requested only for non-residential property over 5 acres.
Where can I find more information on Impervious Cover Limitations?
For more information on Impervious Cover Limitations, please visit Chapter 11 of the Unified Development Code.
What surfaces are approved for driveways, parking, or carports?
Paved Surface. An area surfaced with single or multiple-course surface treatment, asphalt, concrete, pervious concrete, or grasscrete pavement constructed on a base course or similar all-weather surface. Does not include gravel, grass, stones, decomposed granite, or similar unpaved materials. Also does not include existing concrete strip driveways allowed for residential parking areas called “Approved Surfaces” in Section 10.16.010 of the City Code.
To go over the platted impervious cover we can allow permeable pavers to meet both the city code requirements and the TCEQ requirements.
In order to process the request we will need you to provide the following:
- Provide an Engineered Design Water Quality ( Per TCEQ Rules) RG – 34
- Your engineer will need to confirm the runoff coefficients of the pavers and how it affects the drainage criteria and assumptions, this will need to be signed and sealed. Any increased drainage will need to be detained for the 2, 10, 25,100 yr storms. This will need to be in a drainage easement. May need to get the runoff coefficient from the manufacturer.
- There existing TCEQ WPAP will need to be amended or redone to account for the additional BMP(Best Management Practices) (Pavers)
- TCEQ WPAP will need to be recorded and the city provided with a copy of the recordation Receipt
- A Maintenance Agreement following the guidelines in TCEQ RG 348 and the manufacturer guidelines will need to be recorded and go with the property
- A Private Water Quality Easement will need to be recorded and a copy provided to the city
- Detention Easement (If needed)
- Potential 3rd party Inspection to test the infiltration rate.
- Roof Runoff needs to be directed away from the pavers.
- Letter of Completion submitted to TCEQ after installation by the engineer.
Impervious Cover Worksheet
Click here for Impervious Cover Worksheet
For more information on Impervious Cover Limitations
Please Visit Chapter 11 of the Unified Development Code