Stormwater and Drainage Maintenance for Manufactured Home Communities

By Gary E. Wilson, President & Designated Broker, Wilson Management, Inc.

Drainage is the least visible system in a manufactured home community and the one that decides the cost of the most visible one. Roads in the Puget Sound climate do not fail from traffic. They fail from water — water that got under the surface because it had nowhere else to go.

Which means the paving budget is largely set by the drainage budget, several years in advance, whether or not anyone is managing it that way.

This is a practical guide to the system and what it needs.

What a community's drainage actually consists of

Most communities own and maintain everything downstream of the point where water leaves a public system, which typically includes:

• Road drainage — crown, camber, and any kerbing directing water to collection points
• Catch basins and inlets, with their sumps
• Underground conveyance carrying water between structures
• Open ditches and swales along roads and boundaries
• Culverts under roads and driveways
• Detention or retention facilities, where the community has them
• Any treatment structures, where required
• Outfalls where water leaves the site

The extent of this varies enormously with when a community was built. Older communities frequently rely on open ditches and sheet flow; newer ones have engineered systems with detention and treatment. Establishing which you have — and where everything runs — is the first task, and it is not always documented.

Why drainage sits upstream of the road budget

Asphalt fails in a predictable sequence, and every step is water.

A crack admits water. Water reaches the base. A saturated base loses bearing capacity. Traffic over a weakened base produces deformation, then alligator cracking, then a pothole. At that point the failure is structural rather than surface, and the repair is excavation and rebuild rather than patching.

The sequence takes years, and it starts with water that could not get away.

That is why clearing catch basins is not housekeeping. It is the cheapest possible intervention in the road replacement cycle, and it happens years before the cost it prevents.

Standing water in a community after rain is therefore a specific, actionable finding rather than a nuisance. It tells you either that a collection point is blocked, that grading has settled, or that the system is undersized for what it now receives.

Seasonal calendar

Late summer / early autumn — the critical window

• Catch basins inspected and sumps cleaned out
• Inlet grates cleared of debris
• Ditches and swales cleared of vegetation and accumulated silt
• Culverts checked for blockage and structural condition
• Detention and treatment facilities inspected and maintained
• Outfalls checked for erosion and obstruction
• Road surface inspected, with cracks sealed before the wet season
• Downspouts and drainage from community buildings checked

Through winter

• Observation after heavy rain — where does water actually stand?
• Blockages cleared promptly rather than at the next scheduled visit
• Erosion at ditches and outfalls noted
• Ice formation where water ponds

Spring

• Post-season inspection of the whole system
• Silt removed where it has accumulated
• Erosion repaired
• Road damage assessed and scheduled
• Vegetation management before the growing season closes ditches in

Summer

• Paving repair, crack sealing and sealcoating, which need dry weather
• Larger drainage works
• Regrading where settlement has created low points

Observation beats inspection

The most useful drainage information available to a community costs nothing: walk the site during and immediately after heavy rain.

A dry-weather inspection tells you whether structures are clear. A wet-weather walk tells you whether the system actually works — where water stands, where it flows across surfaces it should not, where a ditch overtops, and which culvert is not taking what it should.

Photographing those locations builds a record that is genuinely useful. The same three low points appearing after every significant rain is a design or grading problem rather than a maintenance one, and it will not be fixed by clearing anything.

Where residents come into it

Residents affect drainage more than they realise, and mostly without intending to.

Common issues include landscaping and raised beds that redirect surface flow, sheds and additions placed over drainage paths, gravel or paving added to a site that changes where water goes, plantings that fill a ditch, and yard waste swept into a catch basin.

None of this is malicious and most of it is invisible to the person doing it. The remedy is a rules provision that addresses alterations affecting drainage, communicated at move-in and applied consistently — plus noticing during routine site walks, which is far easier than diagnosing afterwards from the resulting standing water.

See Resident Relations for how rules like this are best administered in a long-tenured community.

Regulatory dimension

Stormwater is regulated, and the obligations attaching to a specific community depend on its size, its discharge, when it was built, and the jurisdiction it sits in.

Communities with engineered detention or treatment facilities generally have maintenance obligations attached to those facilities, sometimes with inspection and reporting requirements. Communities discharging to a municipal system may have obligations under that system's permit.

This article is general information, not legal or regulatory advice.

Older communities and the systems they were built with

A great many Puget Sound communities were built between the 1950s and the 1970s, and their drainage reflects the standards of the time — which is to say, frequently very little of it.

The typical picture is sheet flow across roads to open ditches, culverts under driveways sized for the runoff of a much less developed catchment, and no detention at all. That worked when it was built and works less well now, for two reasons that have nothing to do with maintenance.

The catchment has changed. Development upstream sends more water, faster, than the system was designed for. A ditch adequate for a rural setting in 1965 may be receiving runoff from a subdivision built in 1995.

The community has changed. Sites that were gravel are now paved. Homes have grown, carports and additions have covered ground that used to absorb water, and sheds sit where water used to run. Each individual change was small and the cumulative effect is a community shedding considerably more water than it did.

The practical implication is that in an older community, a drainage problem is not automatically a maintenance failure. Clearing a ditch that is genuinely undersized will not fix it, and repeatedly clearing it while the flooding continues is money spent on the wrong diagnosis.

Distinguishing the two is worth doing before committing capital. A system that works when clear and fails when blocked is a maintenance problem. One that fails after every significant rain regardless of how clear it is has been outgrown, and that is an engineering question.

Planning the capital side

Drainage components have lives like anything else, and they are worth tracking alongside the rest of the community's infrastructure: pipe material and age, catch basin condition, culvert condition, and the state of any engineered facilities.

The sequencing opportunity is significant here. Drainage work and road work happen in the same ground, and doing them together avoids paying twice to open and reinstate the same surface. A community that resurfaces a road and then replaces the drainage beneath it two years later has paid for the same excavation twice — and destroyed a new surface doing it.

That coordination only happens where both sit on a plan. See Capital Planning.

Three things worth doing this year

If a community does nothing else from this guide, these three return the most.

Clean the catch basin sumps. Cheap, quick, and it is the single most direct intervention in the road replacement cycle. A sump full of silt is a collection point that has stopped collecting.

Walk the site in heavy rain and photograph where water stands. Free, and it produces better information about the system than any dry-weather inspection. Repeat it once or twice and the pattern of genuine problem locations becomes obvious.

Seal the cracks before the wet season. Sealing a crack costs a fraction of replacing the section it becomes once water has undermined the base beneath it, and the window for doing it is the dry months.

None of these require engineering input, a capital budget or a consultant. All of them prevent costs that arrive years later at many times the price.

Where to go next

Our Utility Infrastructure page covers the buried systems more broadly, and Mobile Home Park Management covers the wider service.

To discuss your community's infrastructure, contact us or request a free analysis.