Impervious Cover

Overall, the impervious cover permitted under the agreement — 15.9%, or 399 acres — meets the SOS standard, since it includes a small amount of property in the contributing zone, where SOS impervious cover limits are 25% instead of 15%. However, impervious cover can be clustered in a way not envisioned in SOS. Details will be laid out in the agreement’s conservation easement document, which city officials promise is coming soon.

Structural Environmental Control Standards

This refers to how much rainwater is required to be captured, and how that captured water is treated. Applicable regulations will be taken from three Austin ordinances, both past and present.

LIGHT GRAY: SOS Ordinance Area (1850 acres): Development must comply with all SOS impervious cover and structural control limits.

MEDIUM GRAY: Composite Ordinance (1200 acres): This compromise plan, passed in 1991, required proportionately increased capture and treatment of stormwater as impervious cover levels increased.

DARK GRAY: Lower Watersheds Ordinance (32 acres): Under this earlier ordinance, only a half-inch of rainwater is required to be captured and treated.

Lastly, a caveat: Les Tull, water quality engineer with the city’s Watershed Protection Dept., cautions that all numbers cited are estimates and subject to change.

This article appears in February 11 • 2000.

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