Austin critical water quality zones: where you cannot build near a creek

The rule is a prohibition, not a limit

§25-8-261 opens without hedging: "In all watersheds, development is prohibited in a critical water quality zone except as provided in this Division."

This is different in kind from the rest of the code. Floor area, height and impervious cover are ceilings you design under. A critical water quality zone is land you do not build on. If it crosses your lot, the buildable area is what is left over.

Anything that is permitted must be revegetated and restored within the limits of construction, as prescribed by the Environmental Criteria Manual.

How wide it is, by watershed

§25-8-92 writes the boundary three different ways depending on the watershed. They do not reduce to a single table, so here they are separately.

Water supply rural, water supply suburban and the Barton Springs Zone. The boundary coincides with the 100-year floodplain, but is held within these bounds from the centreline:

• minor waterway — not less than 50 ft, not more than 100 ft;
• intermediate — not less than 100 ft, not more than 200 ft;
• major — not less than 200 ft, not more than 400 ft;
• the main channel of Barton Creek — 400 ft, flat.

Suburban watersheds. Fixed distances from the centreline, not tied to the floodplain: 100 ft minor, 200 ft intermediate, 300 ft major.

These may be reduced — to 50, 100 and 150 ft respectively — but only if the overall surface area of the zone is the same or greater than it would have been without the reduction, as prescribed in the Environmental Criteria Manual. It is a reshaping allowance, not a discount.

Urban watersheds. A zone is established along each waterway draining at least 64 acres. The boundary follows the 100-year floodplain, but not less than 50 ft and not more than 400 ft from the centreline.

Lakefront lots are measured differently

Along Lake Travis, Lake Austin, Lady Bird Lake and Lake Walter E. Long the zone runs inland from a fixed contour line rather than from a centreline:

• Lake Travis — the 681.0 ft contour;
• Lake Austin — 492.8 ft;
• Lady Bird Lake — 429.0 ft;
• Lake Walter E. Long — 554.5 ft.

From there the zone extends 100 feet horizontally inland — or 75 feet for a detached single-family residential use. That 25-foot concession is one of the few places in Chapter 25-8 where building a house rather than anything else buys you room.

Along the Colorado River downstream of Lady Bird Lake the shoreline boundary is the ordinary high water mark and the inland boundary follows the 100-year floodplain, held between 200 and 400 feet inland.

What is still permitted

The exception list is short and conditional. In outline:

• A fence, if it does not obstruct flood flows. Unconditional otherwise.
• Open space, if the Watershed Protection Department approves a programme of fertilizer, pesticide and herbicide use. In water supply and Barton Springs watersheds this is limited to sustainable urban agriculture or a community garden, multi-use trails, picnic facilities and outdoor facilities — and expressly excludes stables, animal corrals and athletic fields.
• Trails, subject to width, siting and setback conditions.
• Docks, boat ramps, bulkheads and marinas on the four lakes, under Chapter 25-2 Subchapter C Article 12. For a single-family use, access may not exceed the minimum land disturbance needed for a single route from shoreline to dock.

Where disturbance does occur near a lake, restoration is specified: within a lakefront zone or an equivalent area within 25 feet of a shoreline, at least one native shade tree and one native understory tree per 500 sq ft of disturbed area.

This is a summary of the categories, not the full text. §25-8-261 carries further detailed conditions for each, and §25-8-262 governs crossings.

The drainage ditch exception

Worth knowing because it comes up on infill sites near roads and rail. A critical water quality zone does not apply to a drainage ditch running parallel and adjacent to a railroad or public roadway right-of-way — but all four of these must hold:

• it was designed and constructed primarily to serve that railroad or roadway;
• it is not a segment or modification of a natural waterway;
• it does not possess any natural and traditional character; and
• it cannot reasonably be restored to a natural condition given existing site constraints.

The third and fourth conditions are the ones that fail. A ditch that was once a creek, or that could be restored, keeps its zone.