An infill lot doesn’t give you much room to work with. The parcel sits boxed in by streets, sidewalks, and other buildings. Drainage design on a site like this has to solve a hard problem: where does the water go when there’s barely any open ground left to send it to?
Memphis has a lot of these tight urban parcels, especially in older neighborhoods near downtown and midtown. Many sit next to buildings that went up decades ago, long before current stormwater rules existed. A drainage design here has to work around what’s already there, not around a blank slate.
Where can stormwater leave a tight infill site
Every site needs a place for water to go. On an open lot, that’s usually a pond or a big grassy swale. On an infill lot, those options often don’t exist.
Look at these outlets first:
- The public storm sewer system, if a connection point sits near the property line
- An existing drainage easement that crosses the parcel or a neighboring one
- Curb and gutter systems along the adjacent street
- A combined system tie-in, where older Memphis infrastructure still routes some flow through combined sewer lines
Most infill projects end up tying into the public storm system, since there’s rarely enough land for on-site retention. That connection point needs to get confirmed early. Some blocks in Memphis have limited capacity in the existing storm line, and a project that dumps too much new flow into an already tight pipe can get flagged during plan review.
How does existing pavement change runoff flow
Old pavement changes everything about how a site drains. A parcel that’s been paved for fifty years has a runoff pattern shaped by decades of settling, cracking, and patch repairs.
Before designing anything new, get a topographic survey of the existing pavement grades. Water doesn’t always flow where the original design intended. Settled areas create low spots that hold water. Old patches sometimes sit higher than the surrounding surface, redirecting flow toward a neighbor’s property instead of away from it.
This matters most on redevelopment sites where some existing pavement stays in place. If a new building sits on part of the site and old pavement remains on another part, the drainage design needs to account for both surfaces working together. Mismatched grades between old and new pavement create standing water at the seam, and that seam is usually right where people walk.
What drainage systems fit on small urban parcels
Small sites need compact solutions. A traditional retention pond just won’t fit on most infill parcels in Memphis.
Underground detention works well when surface space is limited. A vault or pipe gallery installed beneath a parking area holds stormwater temporarily and releases it slowly into the public system. It costs more than a surface pond, but it gives back the ground space for parking or building footprint.
Permeable pavement cuts down runoff volume right where it falls. Parking areas and low-traffic drive lanes are good candidates. It won’t handle heavy truck traffic well, so match the surface type to how the space actually gets used.
Bioretention cells, sometimes called rain gardens, fit into small planting strips or unused corners. They’re not a full solution on their own, but they reduce the load on whatever primary system carries the rest.
Most infill projects end up combining two or three of these, since no single system usually handles the full site on its own.
How can the design protect nearby properties
An infill site sits close to its neighbors, sometimes just a few feet away. Bad drainage design here doesn’t just hurt the project. It creates real problems for the property next door.
A few protections matter most:
- Confirm that post-construction runoff doesn’t exceed pre-construction rates at the property line
- Route any surface flow away from shared walls, fences, or foundations
- Coordinate timing with the adjacent property owner if construction will temporarily disrupt an existing drainage path
- Document existing conditions with photos and elevations before construction starts, so any future dispute has a clear baseline
That last point gets skipped more than it should. On a tight infill site, it’s easy for a neighbor to blame new construction for a drainage problem that existed before the project started. A documented baseline protects both sides.
Which drainage approach works best for Memphis infill sites
The right approach depends on how tight the site is and what infrastructure already sits nearby.
For sites near a strong public storm sewer connection, a straightforward tie-in with underground detention usually works best. It keeps the design simple and avoids overloading the existing system. For sites in older neighborhoods with combined sewer segments still in place, a closer look at capacity is worth the extra time. Some of these lines were never sized for the amount of new development happening across the city.
For smaller parcels with tight budgets, permeable pavement paired with a small bioretention area often does the job without the cost of a full underground vault. The right mix comes down to site size, soil conditions, and how close the nearest storm connection actually is.
A drainage design that respects the site’s limits, instead of fighting them, tends to move through Memphis and Shelby County review faster. Reviewers see infill projects often, and they know exactly what a rushed or oversized system looks like on paper.
Frequently Asked Questions
What makes drainage design different on an infill site?
Infill sites have little open space for surface ponds or large drainage areas. Designers often rely on underground storage, permeable pavement and links to existing public systems. The plan must fit drainage needs around buildings, parking and access.
Can a project connect to Memphis’s public storm sewer system?
In many cases, yes. The nearby storm line must have enough capacity for the added flow. That should be checked before the site layout is finalized.
Does old pavement affect a new drainage plan?
Yes. Settled, cracked or patched pavement can send water in directions the old plan never showed. A current topographic survey helps the engineer map those low spots before the new design begins.
What is underground detention used for?
Underground detention stores stormwater below a parking lot, driveway or other paved area. It releases the water at a controlled rate into the public system. This works well on tight sites with no room for a surface pond.
How can a developer avoid drainage disputes with neighbors on a tight lot?
The project team should record existing site conditions before work starts. The new plan should keep runoff at or below the old rate and direct surface flow away from shared property lines. Clear records also help if a drainage complaint comes up later.