French Drains in Johnston, Iowa — Intercepting the Water That Moves Sideways Toward Beaver Creek

Why does the uphill wall of my Johnston basement get wet when it hasn't even rained that hard?

Because the water is moving through the ground toward Beaver Creek, and your uphill wall is in its path. Johnston sits inside the Beaver Creek drainage basin, and the Des Moines Lobe's glacial till doesn't just shed water off the top — it carries it laterally, downhill through the soil, toward the creek. Homes on the descent get wetted from the uphill side by that subsurface flow. It can push against a basement wall days after a rain, or during a slow snowmelt, without any dramatic downpour, because the water is traveling sideways underground rather than falling straight down.

The till here makes this worse than it sounds. The Dows Formation runs 45 to 60 feet deep and behaves unpredictably, holding moisture tightly in its clay fraction while letting water migrate through pockets of sand and gravel. Homes along NW Beaver Drive and the Pioneer Parkway corridor, built mostly between the 1980s and 2000s, are now old enough that their original exterior waterproofing has aged out, and a home down near Camp Dodge sees very different groundwater movement than one on the higher ground toward Pioneer Parkway. Where your lot sits on that slope decides which wall gets the pressure.

So the fix is interception, not just collection. On the uphill side we install an interceptor or curtain drain — a trench of washed aggregate around perforated pipe — to catch the migrating water and carry it around the house before it ever reaches the wall, paired with a footing drain that relieves what's already down at the base. Downspout extensions keep your own roof water from adding to the load, and a catch basin gathers any surface pooling on top. The goal is to cut off the sideways flow at the property's high edge.

Timing is the hard part in Johnston. Iowa's 42-inch frost depth, six inches deeper than Kansas City's, keeps the subsurface frozen well into spring, so meltwater can't percolate down while the water table simultaneously rises to within two or three feet of the surface — a double hit from above and below. We set drain lines below that frost line so they keep working when the ground is still hard. Where water has already come through into the basement, interior drainage and a sump take over, covered on the Johnston waterproofing page.

Cost depends on how much of the uphill perimeter needs interception, how deep the migrating water sits, and how far the collected water must be carried to a safe outlet. Extending downspouts and correcting surface grade is the modest end; a full interceptor and footing drain around the high side runs higher because of the trenching and depth. Every Johnston lot sits at a different point in the Beaver Creek basin, so we price from an on-site look. JLB serves Johnston and nearby Urbandale, Grimes, Polk City, Ankeny, and Des Moines, with Pioneer Parkway and NW Beaver Drive framing the area.