Searches for erosion control and yard drainage in Nepean usually start the same way: a basement wall that is damp after rain, a backyard that stays soft for days, a downspout that has carved a channel in the lawn, or a slope above a creek that is losing ground every spring.
Most of these yards are not a drainage design problem. They are a lot whose original grading has drifted over thirty or sixty years of gardens, patios, sheds and settling. The fix is usually to restore how the lot was meant to drain, which is also the only thing the City lets you do. Here is how we look at it.
The rule that comes first
Ottawa is unusually clear about this. The City’s Landscaping Education Guide says:
“You are not allowed to change the grading of a property. Property grades are designed to direct water away from the home to prevent damage to foundations, flooding to properties, and soil erosion.”
It goes on: all projects must follow approved drainage patterns, and water cannot be directed to neighbouring properties unless that is part of the approved plan. The City’s lot grading FAQ adds that swales are not to be filled, piped or obstructed by landscaping features such as sheds or gardens. Roadside ditches are part of the City’s stormwater system, and the guide’s instruction is short: “Do not alter ditches.”
That rules out the two fixes people try first: filling the wet swale and sending the water next door. It leaves plenty of fixes that work.
Find your grading plan. If one exists, the City says you can request it through its access to building permit records service. Many older Nepean lots have no plan on file; in that case the guide says to call 3-1-1 for guidance.
Why Nepean yards hold water
Two things are true of most of Nepean.
The ground is clay. Much of the Ottawa Valley sits on Leda clay, a fine marine clay left by the Champlain Sea that holds a lot of water and drains slowly. Water that cannot run off the surface sits in it. That is why a low spot in a Nepean lawn stays wet for days, and why a buried soakaway pit, which works in sandy soil, tends to fill up and stay full here.
The houses are older. Much of Nepean was built between the 1950s and 1980s. After that many years, the grade beside the foundation has often settled, garden beds have been built up against the siding, a patio or deck has blocked the swale, and downspouts discharge wherever they were last pointed. None of it was a decision. It accumulated.
Reading the yard
Walk the lot during or just after a heavy rain. What you see tells you which fix you need.
Water against the foundation. If the soil slopes toward the house, or is level with it, water runs to the wall and down it. This is the most important one to fix, and usually the simplest.
A soggy swale. The shallow channel along the side or rear lot line is meant to carry water to the street or a rear-yard catch basin. If it holds water, it has usually lost its slope: silted up, built over or crossed by a garden bed or fence.
Erosion at a downspout. A bare channel or hole where a downspout lets out means concentrated roof water with nowhere to spread.
Standing water in the middle of the lawn. A low spot, often over an old trench or where a tree came out, sitting in clay that cannot absorb it.
Ice on the walkway or driveway every winter. Usually a downspout or sump outlet discharging across the path. It is also a common cause of sunken interlock.
A slope losing ground. Bare soil, rills after rain, or a bank above a creek that is undercutting. This is erosion, and it is a different conversation, below.
The fixes, roughly in order of cost
1. Restore the grade at the foundation
Strip back mulch and soil that has built up against the siding, fill and compact so the ground falls away from the house, and replant or resod. The grading plan, where one exists, sets the slopes. This is restoration, not regrading, and it is the single most effective drainage fix on most older lots.
2. Route the downspouts
Each downspout should discharge onto a splash pad or extension that carries water away from the foundation and toward the swale, on your own property. Not onto the neighbour’s lot, not across a walkway, not into the side yard where it pools against the next house. Sump pump discharge follows the same logic. The guide is explicit that water cannot be sent to neighbouring properties.
3. Re-establish the swale
Remove what has built up, re-cut the channel to its slope, and resod it. Where a fence, shed or garden bed is sitting in the swale, the City’s guidance is that it should not be. On a shared side-yard swale, talk to your neighbour first; the water is going to cross both lots either way.
4. Fill low spots
Low areas in the lawn are filled with screened topsoil, compacted lightly and resodded so they shed water like the rest of the yard. Our guide to sod installation on clay covers why the soil underneath matters as much as the sod.
5. Subsurface drains
Where the surface is right and the ground still stays saturated, a French drain (perforated pipe in clear stone, wrapped in filter fabric) can collect water below the surface. On clay, the design question is the outlet: the pipe needs to run to a lower point in your approved drainage pattern, such as the swale, so it can empty. A drain that ends in a buried pit in the same clay does not.
A channel drain across the bottom of a driveway or at the edge of a patio catches surface water that would otherwise run toward the garage or the house.
6. Plumbing-side protection
Backwater valves and sump pumps protect the basement from the sewer side. That is plumbing work rather than landscaping, and the City runs a Residential Protective Plumbing Program that offers rebates for eligible homes. If your basement water is coming up through the floor drain rather than through the wall, start there.
Erosion control on slopes and creek lots
Nepean has a lot of sloped and ravine lots: along the Rideau River, on the creek corridors that run through the older neighbourhoods, and on the Jock River side of Barrhaven. Erosion on these is a mix of surface water and gravity, and the fixes scale with the slope.
Gentle slopes with bare soil. Get water to the slope spread out rather than concentrated, then cover the soil. Deep-rooted groundcovers, native shrubs and a biodegradable erosion-control blanket over seeded or planted soil hold the surface while roots establish. Mulch alone washes off a real slope.
Concentrated flow. Where a downspout, sump outlet or swale empties onto the slope, armour the outlet with stone so the water spreads before it reaches the soil, or bring it down in a lined channel.
Steeper slopes. Terracing with low retaining walls breaks a slope into level beds that hold soil and slow water. Walls need proper base, drainage behind them and geogrid where height requires it, which our guide to retaining walls that last in Ottawa covers. A retaining wall over 1 m high next to an access to the building needs a building permit; our permits guide has the details.
Creek banks, ravines and anything that is actively slumping. Stop and call before digging. Nepean is in the Rideau Valley Conservation Authority’s watershed, and the RVCA says projects that alter property near a waterbody, wetland, steep slope or floodplain may need its approval. Its list of regulated activities includes site grading and placing or removing material, which covers most erosion work. The RVCA’s resource specialists are at 613-692-3571, and the RVCA recommends talking to them before you apply. On sensitive marine clay, a slope that is moving, as opposed to eroding at the surface, is a job for a geotechnical engineer first and a landscaper second.
Before any digging
Provincial law requires locates through Ontario One Call before you dig, even with a hand shovel. Gas, hydro, cable and water service lines often run exactly where a swale or French drain wants to go. Trees matter too: grading over the roots of a protected tree can breach the City’s tree protection rules.
Drainage when you are already building
The best time to fix drainage is when the yard is open anyway. A new patio has to be built as part of the lot’s drainage, sloping away from the house and below the door sill. A new lawn is the moment to restore the grade. A backfilled foundation is the moment to get the fall right against the wall. If a larger project is coming, sequence the drainage into it rather than doing it twice. Hardscaping in Nepean and what landscape construction includes cover how the pieces fit together.
Drainage and erosion work in Nepean
We regrade to the approved pattern, rebuild swales, install French and channel drains, route downspouts, fill and resod low areas, and build planted slopes and terraced retaining walls across Nepean, Barrhaven, Kanata and Stittsville. The full scope is on our landscape construction page.
Book a free on-site estimate. We will walk the lot with you, show you where the water is going and why, and give you a fixed price for putting it back where the lot was designed to send it.
Published October 25, 2026 by ALM Construction & Landscaping. General information for Ottawa-area homeowners, not a substitute for the City's determination on your specific project.