How do you fix a yard that floods or holds water?

Why does standing water sit in a yard with clay soil?

Because clay takes water in far more slowly than a storm delivers it. San Gabriel Valley drainage starts with that fact: the ground under much of the valley is expansive clay, and most of our rain arrives between roughly November and March, often in short, heavy storms. The surface saturates quickly, and everything after that runs across the ground to the lowest place it can reach: a hollow in the lawn, a patio corner, or the strip of soil along the house.

Clay explains why the water stays; the shape of the lot explains where it goes. Many Pasadena houses are close to a century old, and in that time the ground around them gets rearranged. Backfill along the foundation settles into a shallow trough, patios get poured flat or tipped toward the walls, planter beds are built up against the house, and downspouts are left emptying a whole section of roof onto one spot. Each of those either sends water toward the house or keeps it there.

How do you find out where the water is coming from?

Watch it happen. One storm observed from start to finish tells you more than any theory, because the source is often somewhere other than the puddle: a downspout two corners away, runoff from a neighbor's lawn, or a walk that tips the wrong way and feeds the one low spot in the yard. Take notes as it happens; the flow paths vanish when the rain stops, even if the puddle stays.

Timing is a clue as well. A spot that stays wet in August, months after the last real rain, is not a weather problem; it points to an irrigation leak, a cracked water line, or a valve that sticks open. Bring your notes to any yard drainage contractor in Pasadena you talk to. One who proposes a French drain before asking where the water starts is guessing.

• Stand outside in heavy rain and trace each stream back to where it begins.
• Note where every downspout empties and how far its water spreads.
• Check which way the patio, walks, and driveway tip once they are wet.
• Run a hose at the highest point of the yard on a dry day and follow it.
• Push flags into the low spots so you can find them after they dry.

Is the water putting your house at risk?

It is when water collects against the foundation or reaches the bottom of the walls; a soggy lawn by itself is mostly an annoyance. Water pooling against the house soaks the clay under the footings, and clay that swells every winter and shrinks every summer moves whatever rests on it. Over years that can show up as cracked slabs and doors that bind in one season and swing freely in the next.

Stucco houses have a second weak point at the weep screed, the metal strip along the bottom edge of the stucco. The code places it at least 4 inches above soil or 2 inches above paving, so water that gets behind the stucco can drain out. When a planter bed or years of mulch rise above it, the wall starts taking water in from the soil instead. We find buried screeds often, and clearing them costs little compared with what they protect.

• Water pooling against the house for hours after a storm.
• Soil, mulch, or a planter bed sitting above the weep screed.
• A white, powdery crust on the foundation or the bottom of the stucco.
• Damp soil, standing water, or a musty smell in the crawl space.
• Downspouts emptying within a step of the foundation.

Why start with the gutters and downspouts?

Because the roof is often the largest single source of water on the lot, and the downspouts decide where all of it lands. A roof gathers rain over its whole footprint and delivers it to a few corners, so a downspout emptying onto a splash block beside the foundation puts that entire flow where the house can least afford it. When backyard flooding in Pasadena traces back to one corner of the house, look up before you dig.

Downspout drainage is often the least expensive fix that makes a visible difference. We tie each downspout into buried pipe that carries the water across the yard to an outlet, with a cleanout so the line can be flushed. The gutters need attention first: cleared of leaves, sloped toward the downspouts, and sealed at leaking seams, because a gutter that overflows drops water along the whole length of the wall instead of at the corners.

You can test the idea for almost nothing. Clip a flexible extension to the suspect downspout, run it well out into the yard before the next storm, and see whether the problem spot stays dry. If it does, you have found your source, and the permanent fix may be a pipe rather than a regrade.

What does grading away from the foundation actually look like?

It looks like ground that falls at least 6 inches within the first 10 feet out from the house, which is the residential code's standard for lot drainage. That is enough fall to check yourself with a string line and a level. On many older lots the fall has reversed: the soil against the wall now sits lower than the soil a few feet out, so the house stands in a shallow moat every time it rains.

Near a house, regrading usually means taking soil away rather than piling it on, because the weep screed, or the bottom of the siding on a wood-sided Craftsman, limits how high the ground can come. We pull planter beds and old mulch down until that line is clear, fill any settled trough only as high as it allows, then lower the ground farther out so the whole band falls away from the house. Hardscape against the house gets the same test: a walk or patio edge that tips toward the foundation has to be corrected, or it undoes the grading beside it.

Narrow side yards are the hard case, because there is rarely 10 feet of ground before the fence. The usual answer there is a shallow swale shaped down the length of the side yard, carrying water to the front or back. The side yard on the Menlo Backyard was rebuilt to move water away from the structure, and on a tight lot that strip often decides whether the house stays dry.

French drain, channel drain, or catch basin: which one fits?

The one that matches where the water is. A catch basin, the usual surface drain, is a box with a grate, set at a low spot in a lawn or planting bed and tied to buried pipe; it suits a yard that collects water in one or two places. A channel drain is a narrow grated trough set into paving, and it belongs where a patio, walk, or driveway sheds water toward a door, a garage, or the house.

A French drain works below the surface: a gravel-filled trench with a perforated pipe at the bottom that gathers water moving through the soil. It suits ground that stays soggy after the surface dries, or a band where water seeps in from higher ground. It gets suggested for everything, but it is the wrong tool for a puddle sitting on hard clay, which needs a surface inlet to reach a pipe at all.

Many yards end up with a combination: inlets at the low spots, a channel drain at a patio edge, and everything feeding one solid line to the outlet. The pipe should be sized for what a heavy storm puts on the roof and paving it serves, because an undersized line backs up exactly when you need it.

Where is the water allowed to go?

To a lower point on your own property or, with approval, to the street. Yard water generally cannot go into the sanitary sewer or onto a neighbor's property. Settle the outlet before anything else is designed, because its height decides whether gravity can do the work: every pipe in the yard has to fall toward it, so an outlet that sits too high can rule out a whole drainage plan.

In Pasadena, a curb outlet typically needs approval from the city's public works department, and in Altadena the county handles it, so confirm the rules and get the approval before anyone cuts the curb or trenches the parkway.

Dry wells, buried pits of rock meant to let water soak away slowly, come up often, and on clay they struggle. They fill in the first storm and stay full, because the ground around them will not take the water. Where the soil drains better one can work, but we would want to see a test hole drain before relying on it.

• Daylight on your own lot, at a lower spot where water can spread over rock.
• A curb outlet under the parkway, once public works has approved it.
• Never the sanitary sewer, including a downspout tied into a sewer cleanout.
• Never a neighbor's property, even when it sits lower than yours.

When does fixing yard drainage become a bigger project?

When the water has nowhere lower to go. If the low spot sits below the curb and below every point on the lot you could daylight to, gravity cannot move it, and the answer is a sump: a basin at the low point with a pump that lifts the water into a pipe running to an approved outlet. A new outdoor circuit to run that pump generally needs an electrical permit.

A pump brings a machine's weak points into the yard. It needs a check valve so water does not run back, a basin you can reach to clean, and a test before each rainy season, and it stops when the power fails, which can happen in the same storm that is filling the basin. A battery backup helps. We use pumps only where the grade leaves no gravity option.

The other big versions involve water from beyond your lot or under your house. A neighbor's downspouts or sprinklers draining your way call for a conversation first and an intercepting drain along the shared line second. Standing water in a crawl space, or a hillside above the house that sheds across the yard, means the grading and the foundation have to be looked at together, and that deserves a full site plan rather than one more drain.