Drainage Charge: How is it calculated?

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 is $0.00498 per square foot of impervious cover. 

Impervious Cover

The impervious cover for each property includes surfaces like rooftops, driveways, parking lots, walkways, patios, unpaved driveways and unpaved parking. 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