Entitlement guide
Drainage and detention: where the water goes when you pave.
Adding roofs and paving sends more water downhill, faster. Most jurisdictions want proof that your project does not make things worse for neighbors.
The short answer
Drainage rules ask a simple question: after development, does the site send more water, or send it faster, than before? If so, you usually need detention, a pond or underground storage that releases water slowly. Some areas also require water quality controls to remove pollutants.
The details live in each city's or county's drainage criteria manual. The design, the calculations and the seal come from a licensed civil engineer. VALITER flags what is likely to be required and how much land it may take, early, so it is not a surprise.
- Which drainage criteria manual applies
- Whether detention is likely, and a rough land estimate
- Water quality controls from watershed or aquifer rules
- Floodplain on or next to the site
- Signs of downstream constraints in public data
- Where drainage review falls in the approval sequence
Why it can stop a deal
Where projects get caught.
Detention takes land
A pond can take a meaningful share of a small site. Underground storage saves land and costs more.
Downstream problems
If downstream channels or culverts are already undersized, the reviewer may ask for more analysis or more storage.
Overlapping rules
Watershed, aquifer and floodplain rules can stack on top of drainage criteria, each with its own controls.
How it works
How it usually works in Central Texas.
Rules differ by city, county and utility, and they change. Treat this as orientation and confirm with the approving authority.
Criteria manuals. Cities and counties adopt drainage criteria that set storm events, methods and release rates. They differ across Central Texas, so the same site plan can need different detention in two neighboring jurisdictions. Some cities allow fees in lieu of on-site detention in certain areas, after a study shows it will not harm downstream property.
Downstream analysis. Reviewers often want to know where water goes after it leaves the site and whether it causes harm there. That can mean studying channels, culverts and neighboring property. The extent depends on the jurisdiction and the size of the change.
Water quality. In sensitive watersheds and over the Edwards Aquifer, state or local rules can require permanent controls such as sand filters, vegetated filter strips or ponds that capture the first flush of runoff. These are separate from detention, though one facility sometimes serves both purposes.
Floodplain. Work in a mapped floodplain is its own review, with its own permit. Drainage design must also respect any floodplain on or next to the site.
How VALITER handles it. Drainage is a professional gate. We identify the criteria that apply, estimate the area detention and water quality controls may need, and flag downstream concerns we can see in public data. Your civil engineer designs, calculates and seals the plan.
Who decides
The people and offices involved.
| Who | What they decide |
|---|---|
| City or county engineering staff | Drainage review and approval under local criteria |
| Floodplain administrator | Floodplain development permits |
| TCEQ | Edwards Aquifer protection plans where they apply |
| Civil engineer | Drainage design, calculations and seal (a professional gate) |
- Which drainage criteria apply to this parcel?
- Is detention required, or is a fee in lieu possible here?
- Are water quality controls required by watershed or aquifer rules?
- What downstream analysis will the reviewer expect?
- How much land should we hold for ponds or controls?
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