Stormwater and Utility Coordination in McKinney’s High Growth Subdivisions: Avoiding the Common Redesign Trap

What is the redesign trap?

Design in sequence, then find the conflict after the layout is fixed. The site planner sets lots and streets, the drainage engineer drops a pond in the low corner, and the utility designer gets the plan last. The low corner was also where the sewer wanted to go.

By then the fixes are expensive: a deeper sewer, a lift station that was not needed, an easement through lots, a moved pond, or fewer lots. Each one means revised plans and another review cycle. The cure is not more effort. It is doing the same work in a different order.

Where does each pipe go in a McKinney street?

The manual sets the street section, so start there. Section 5.1.D of McKinney's Engineering Design Manual (Revision 7, adopted May 5, 2026) gives the typical layout:

• Water mains on the north or east parkway, 4.5 feet behind the back of curb.
• Wastewater mains along the roadway centerline on residential and collector streets.
• Storm mains along the centerline of the outside travel lane farthest from the water main.
• On arterials, water and wastewater mains outside the right-of-way, in their own easements.

Mains stay out of alleys unless the Director of Engineering approves, and at least 5 feet from power poles. Storm drain pipe on public facilities is reinforced concrete, Class III or higher, with at least 1 foot of cover and never in the roadway subgrade.

Arterials are where lot yield goes. Water and sewer easements outside the right-of-way come out of the lots or open space along the frontage. Draw them before the lot lines are final.

What happens where storm drains cross water and sewer?

Encasement, and the vertical room to build it. Section 5.1.F requires a steel encasement pipe on the water or sewer line where a storm pipe or culvert over 48 inches in span crosses above it. A smaller storm pipe, or one passing under the line with less than 2 feet of vertical clearance, gets a concrete encasement.

The encasement extends at least 10 feet beyond the outside edge of the storm pipe or box culvert. Steel encasement is at least ½ inch thick, and concrete at least 6 inches.

State rules sit underneath. The manual sends water and sewer separation to TCEQ, where 30 TAC §290.44(e) sets the 9-foot separation between new potable water lines and wastewater facilities. A subdivision with trunk storm lines converging on a pond can have dozens of these crossings. Check every one in profile during layout, not at plan review.

How wide do the easements have to be?

At least 15 feet, and wider as the pipe gets deeper. Water and wastewater easements are 15 feet minimum under Section 5.1.G. For mains deeper than 10 feet to the bottom of pipe, the width is 2.5 times the depth, rounded up to the nearest 5 feet, with more for pipe over 36 inches.

Drainage easements follow Section 4.1: 15 feet minimum, and for storm mains deeper than 10 feet, 2.5 times the depth plus the pipe width, rounded up to the nearest 5 feet.

In residential developments, water and wastewater mains may not cross residential lots, and their easements must sit entirely on one side of a fence or property line. A deep sewer pushed out of the street by a pond can therefore cost a full lot width, not a sliver.

How does McKinney size detention?

For the fully developed 100-year storm, with outlet control at two storms. Section 4.10 says new development follows the 10 percent rule in NCTCOG's iSWM manual. A downstream assessment checks capacity and easements to the point where the site is 10 percent of the watershed, and is unnecessary when the development is less than 5 percent of the watershed at its outfall.

If downstream capacity or easements are missing, the developer builds the improvements, obtains the easements, or detains on site. Where detention is used:

• storage is sized for the 100-year storm on fully developed watershed conditions;
• the outlet controls both the 5-year and 100-year storms to pre-project levels;
• side slopes are no steeper than 4H:1V unless a geotechnical engineer approves;
• the bottom drains at 2 percent minimum to a pilot channel;
• a maintenance ramp at least 12 feet wide and no steeper than 8H:1V is provided.

Those slopes and the ramp set the pond's footprint, not just its volume. A pond drawn as a blob on a concept plan usually grows when it is graded to these rules. Also, rerun hydrology on the manual's current Collin County rainfall table (Table 4-1) before you reuse a pond size from an older job.

What if the site needs a lift station?

Then its access has to survive the storm the pond is built for. McKinney's manual allows a lift station only with the Director of Engineering's approval, after gravity options are investigated, as we covered in our McKinney utility availability study post.

If one is approved, 30 TAC §217.59 requires the site to be accessible by truck in all weather, including a 25-year, 24-hour rainfall, over a road at least 12 feet wide, and the station to withstand and operate during a 100-year flood. Do not route that access road through the pond's overflow path.

When should stormwater and utilities be coordinated?

At the concept plan, on one survey. The manual requires storm drainage plans as part of the platting process, coordinating on-site and off-site flows for storms up to the fully developed 100-year event. The water and sewer layout fights for the same low ground and corridors, so build both on the same base map.

A practical order for a McKinney subdivision:

1. Get the survey, drainage areas and downstream assessment started together.
2. Find the sewer outfall and the pond's likely spot, and settle who gets the low ground.
3. Draw the street sections from Section 5.1.D, with arterial easements.
4. Grade the pond to Section 4.10 slopes, ramp and freeboard.
5. Profile every storm crossing and mark encasements.
6. Size every easement by depth, then set the lot lines.

A note on limits: this is general education from McKinney's Engineering Design Manual, Revision 7, and state rules as of October 2026. The Stormwater Management Ordinance (Article 8 of the Unified Development Code) and the Director of Engineering govern your project, so confirm the criteria with the city.

Frequently asked questions

Can a water line run inside a McKinney detention pond easement?

The manual does not give a blanket rule. Water and wastewater mains outside the right-of-way need their own easement sized by depth, and pond maintenance access must stay clear. Ask the Director of Engineering early if you want them to share ground.

Does every McKinney subdivision need on-site detention?

No. Detention is one way to meet the 10 percent rule. If the downstream assessment shows enough capacity and easements, or the developer builds the downstream improvements, on-site detention may not be needed.

I'm a developer with two firms on my McKinney subdivision, one for drainage and one for utilities. How do I stop the conflict from falling between their contracts?

Put one person in charge of the combined layout, and write joint milestones into both scopes: shared base map, a crossing check and an easement layout before the preliminary plat. Better still, hire one civil team for both.

I'm the land planner on a 150-lot McKinney tract, and the concept plan puts the pond in the only low corner. What should I ask before I finalize lots?

Ask where the sewer outfall must go and how deep the trunk will be, whether gravity works without that corner, and how big the pond becomes once graded to 4H:1V slopes with a 12-foot ramp.

Related resources

• McKinney's 2026 Engineering Design Manual: Utility Changes Developers Need to Catch Before Plan Submittal
• Shrink Swell Clay Soils in Collin County: Engineering Buried Utilities for Blackland Prairie Conditions
• Water Storage and Pressure Zone Design for McKinney's Rolling Terrain: Engineering for Collin County Topography
• Drainage studies with sealed hydrology and hydraulic calculations

Laying out a McKinney subdivision before the plat?

We lay out drainage, detention, water and sewer together on one base map, so the pond, the crossings and the easements fit before lot lines are set.

We specialize in:

• Site civil design for land development
• Drainage studies and detention design
• Water and sewer utility design
• Lift station design
• Easement and plat coordination
• Construction administration

Modern Engineering Solutions, McKinney, Texas. Contact: (214) 833-6748 or mod-eng.com