10d • General discussion
Why drainage is the most expensive mistake in land development
Drainage will make or break your subdivision. Here is why.
On a 47-lot project I engineered in Weslaco, TX (Angelica's Dream V2), 100% of the site sits in FEMA Zone A. That means every square foot of the property is in the floodplain.
What that means for development:
1. You cannot just grade the site and call it done. You need a full drainage study, detention design, and possibly a CLOMR/LOMR with FEMA.
2. Every cubic yard of fill you bring in displaces floodwater somewhere else. You have to prove to the city and FEMA that your project does not make flooding worse for your neighbors.
3. Detention ponds cost money and eat lots. On the Conway Mile3 project, we dedicated an entire commercial lot (43,400 SF) to detention. That is land you cannot sell as a residential lot.
4. Storm sewer pipe is expensive. On that same project, storm drainage cost $125,000, which is about 15% of total construction.
Common drainage mistakes I see from new developers:
Buying land in a floodplain without understanding the cost to get out of it. A CLOMR alone can cost $30K to $80K in engineering fees, and take 12 to 18 months for FEMA review.
Assuming the city will accept sheet flow off your lots into the street. Most cities in the RGV require on-site detention for any project over 1 acre.
Not coordinating drainage with your paving design. Your road profile IS your drainage system. If you do not design them together, you end up regrading after the road is built.
The bottom line: always get a drainage study before you close on the land. $5K on a study can save you $200K in surprises.
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Why drainage is the most expensive mistake in land development
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Raw dirt to shovel ready. A licensed Civil Engineer breaks down real projects, real numbers, and lessons from the field. www.ferest.dev
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