Stormwater and Drainage Construction in Amarillo

Detention ponds in Randall County have no owner unless someone creates one. The county's 2023 subdivision regulations say plainly that the county will not maintain retention and detention facilities, and that a perpetual entity such as a homeowners association must. For a developer or a commercial owner, that sentence changes how a drainage plan is drawn, financed and handed over.

The land makes the problem harder. The Panhandle is flat, the soil drains slowly and many of the low spots are playa basins that hold water for weeks. When a storm hits Amarillo, the water has few places to go, and a good deal of it ends up in the city's pump system. A site that drains well on paper can still flood a neighbor or itself if the design ignores where the water goes after it leaves the pond.

We build storm sewers, inlets, culverts, swales, detention basins and outfalls for commercial, industrial and institutional projects in Potter and Randall counties and the surrounding Panhandle. The notes below describe the rules, the field conditions and the choices that move cost.

Authority over drainage depends on where the parcel sits. Inside the city, the City of Amarillo reviews drainage with the building permit. In the unincorporated parts of Randall County, the subdivision regulations require drainage easements out to the limits of the 100-year floodplain. Potter County's regulations, revised by the Commissioners Court on December 11, 2023, require a plat to include a comprehensive drainage plan that identifies any 100-year floodplain and recommends minimum foundation elevations for lots at elevated flood risk.

Floodplain permitting is separate. Randall County's floodplain office says no construction can begin without a Floodplain Development Permit, with a Class A permit for development outside the mapped 100-year floodplain and a Class B permit for development partly or fully inside it. Land in Amarillo's extraterritorial jurisdiction adds a step, because the city has exclusive authority to approve or deny plats for streets, alleys and drainage there. We map which of these apply before we price a drainage package, since each one changes the schedule. Large parcels in the south Amarillo business park area near Loop 335 and I-27 often sit where the city and county rules meet.

Look at what the city itself is doing. In June 2023, six Amarillo playa lakes were being pumped at maximum capacity, with the water moving to creeks, the Canadian River and eventually Lake Meredith. The city's public works director said all playa lakes except Martin Road Lake were at or above capacity, and linked part of that to heavier rainfall in southwest Amarillo. The city reported more than $1 million in damages across the two counties.

In September 2025 the City Council approved design services for a Lawrence Lake drainage project at the playa off I-40 and Western Street, with a new pump station that sends stormwater to West Amarillo Creek. The work is expected to take at least two years once design is final. A private site that sits near a basin like that is not just reading a map, and a large distribution center pad in the same watershed needs the same care. It is part of a system the city is still working to fix, and the owner should assume that conditions may change over the life of the building.

Our drainage scope runs from the first pipe to the last inlet. We build storm sewer trunks and laterals, curb and area inlets, junction boxes, headwalls, culverts, concrete flumes, swales, detention and retention basins, outlet structures and rock or concrete energy dissipators. We also install the erosion controls that keep a basin from filling with silt before the building opens.

Grades come first. A pond or swale that is a few inches off will pool water where it should not, so we survey as we build and check the invert elevations at every structure. The mass grading trade partners set the pad and basin grades to the same control. On larger developments, drainage is one element of site development and utilities, and we build it as part of the same sequence so trenches are not opened twice. Where the basin sits next to a loading area, we coordinate with truck court and dock apron construction so that heavy wheel loads do not damage outlet pipes.

Cost depends on pipe size and depth, the number of structures, rock, dewatering and how much land the basin takes. Pipe is the visible cost. Land is the hidden one. Every acre given to detention is an acre that cannot hold a building or a lot, and some owners are surprised to learn that a flat site may need a large pond because there is no slope to move water away fast.

Clay and shallow caliche also change trenching costs. Pullman clay shrinks and cracks when dry and swells when wet, and the Randall series soils on playa floors are very slowly permeable and often ponded for long periods. Trench backfill in clay needs care, and basins in those soils may hold water longer than a plan assumed. We recommend a geotechnical report that tests infiltration rates, not just bearing, before the basin is sized.

We sequence drainage first, because everything else depends on it. Basins and outfalls go in before the pad is finished so that construction runoff has somewhere to go. Storm trunks go in before base course so no one has to cut a new pavement. Inlets and cleanouts are protected throughout, and we inspect them after every significant rain.

After handover, the owner still has work to do. Basins need mowing, sediment removal and inspection of outlet structures, and the entity named in the plat is responsible for it. Property management firms tend to inherit these basins, so we give owners a plain maintenance sheet that lists what to check, how often and what a failing outlet looks like. Owners with several sites can use this work as part of a multi-site rollout so each location follows the same drainage details.

Send the plat, the drainage study or just the address. We will tell you which approvals apply and what a basin, outfall and storm sewer package is likely to cost.

Who maintains a detention basin on a private commercial lot?

The owner does. In unincorporated Randall County the county states it will not maintain detention or retention facilities, and a perpetual entity must. We hand over a maintenance sheet so the owner knows what to inspect, when to remove sediment and how to protect the outlet.

Can I build on a lot that borders a playa lake?

Sometimes, but the design must account for ponding. Playa floors can hold water for long periods, and the city has had to pump them in wet years. Floor elevations, access drives and the drainage plan all need to be checked against the playa high-water level before you buy.

Do I need a floodplain permit?

Randall County requires a Floodplain Development Permit before any construction, with a Class A permit outside the mapped 100-year floodplain and a Class B permit for development in or partly in it. Inside the city, Amarillo handles floodplain review through its own permits. Ask before you close.

How long does drainage design and approval take?

Plan on weeks for design and more for review. Potter County plats need a drainage plan, and plats in the city extraterritorial jurisdiction need city approval first. We help owners line up the engineer and the reviewers early so earthwork can start when the approvals are in.

Is detention always required?

Not always, but on flat land with slow soil it often is. Whether it applies depends on the jurisdiction, the downstream capacity and the site layout. We would rather check the rules before design than redesign a pond after the permit comes back.