Most asphalt in the metro does not wear out from the top. It fails from underneath, because the ground here holds water and the climate freezes it. The glacier that stopped at Des Moines about 14,000 years ago left a thick layer of clay-rich till and a landscape that drains slowly, and a modern lot adds water of its own, from downspouts, sump lines and the snow that city rules keep off the street. This guide follows that water: where it comes from, where it sits, when it does its damage, and which fixes pay off in what order.
The figures come from the Iowa Geological Survey, USDA soil series descriptions, NOAA's 1991-2020 normals for the Des Moines airport station, and the City of Des Moines. Monthly weather tables are on the Des Moines pavement numbers page. None of this needs a soil lab. An owner with a tape measure, a rainy afternoon and a notebook can work out most of what follows.
What the glacier left under the metro
The Des Moines Lobe was the last ice sheet to enter Iowa. The Iowa Geological Survey says it advanced in surges beginning about 15,000 years ago, reached its southern limit at the site of modern Des Moines about 14,000 years ago, and had melted away by 12,000 years ago. The Bemis end moraine marks the limit of that first great advance. Everything the lobe deposited is grouped as the Dows Formation: 45 to 60 feet of glacial drift over older deposits, with dense, pebbly loam near the bottom.
What the ice did not leave was a working drainage system. The survey describes the lobe as a young landscape with sluggish, inefficient drainage; nearly all of Iowa's natural lakes lie on it, and its low spots still hold dark, poorly drained soils where water once ponded. Farmers made that land productive by clearing boulders and laying tile lines under the wet areas. Suburbs to the north and west of the city are built on the same ground, and a buried tile line or a filled-in wet spot can still steer water under a driveway decades later.
Beyond the ice margin the landscape changes. The Southern Iowa Drift Plain is built on glacial deposits more than 500,000 years old, carved by long erosion into rolling hills and valleys and capped with 5 to 30 feet of wind-blown loess. The metro sits where the two landscapes meet, so soil conditions can differ from one part of it to another, and a rule of thumb that holds on flat till may not hold on older, loess-capped ground.
Four soils, four water tables
USDA's official series descriptions show how the lobe's soils change over a few feet of relief. Clarion and its catena partners run from the rises down to the flats, and Okoboji fills the closed depressions below them. The difference that matters for pavement is how close to the surface each one stays saturated in a normal year.
Those depths matter because a driveway's stone base sits within about a foot of the surface: HomeGuide's residential standard is 2 to 3 inches of asphalt over 6 to 8 inches of compacted gravel. On Clarion ground the spring water table stays well below the stone. On Webster or Okoboji ground, water can sit in the base itself during the wettest part of the year. One subdivision lot can hold both, with a rise at the house and a flat at the street, which can leave one end of a drive cracking and sinking while the other stays sound.
Identifying the soil under a lot does not take a lab. The USDA's Web Soil Survey lets anyone draw an area of interest around a property and see the mapped soil series. The ground also gives its own clues: darker, heavier soil in low spots, water that lingers in the lawn after rain, and a sump pump that keeps running well into spring all point to the wetter end of the sequence.
- Clarion: moderately well drained, on rises; saturated at 4 to 6 feet from March to June; loam till with 18 to 28 percent clay
- Nicollet: somewhat poorly drained; seasonal saturation as high as 1.5 feet below the surface
- Webster: poorly drained, on broad flats; saturated within about 8 inches in a wet season when undrained; 29 to 39 percent clay near the surface
- Okoboji: very poorly drained, in closed depressions; frequently ponded for long periods; series established in Polk County in 1958
Why March does the most damage
Pavement engineers list three conditions for frost heave: a frost-susceptible soil, subfreezing temperatures and a supply of water. The standard Casagrande screen flags a soil as frost-susceptible when just 3 percent of it passes a 0.02-millimeter sieve, and lobe till with a fifth or more clay far exceeds that. As the ground freezes, water drawn up through the fine soil builds ice lenses that lift the pavement. When they melt, the soil left behind is wetter and weaker than before, and Pavement Interactive notes that a thawing subgrade loses much of its bearing capacity.
The calendar stacks those conditions in March. NOAA's normals for the airport station give March 15.5 freeze-thaw days, tied with December for the most of any month, along with 5.2 inches of snow and 2.30 inches of total precipitation. April follows with 3.86 inches of precipitation and 4.9 more freeze-thaw days, and the median last freeze does not arrive until April 17. Meanwhile Clarion soils are in their saturated season, which runs from March through June.
That is the window when driveways break. A crack that let water in during February becomes a heaved ridge, and a soft spot at the end of the drive becomes a pothole under the first heavy delivery truck of spring. Road agencies respond to the same physics by cutting allowed loads during the thaw. A homeowner cannot post a load limit, but can keep the heaviest vehicles off the weakest part of the drive until it firms up, and can make sure nothing adds extra water to it.
Water a Des Moines lot adds on its own
Roofs come first. A downspout that empties onto the drive, or beside its edge, delivers the runoff from a whole section of roof to the place where it does the most harm. The City of Des Moines recommends pointing downspout and sump pump outlets toward the front or rear of the house, into areas that drain away from structures, with the outlet at least 15 feet from the building and from adjoining property lines. Sump water must never go into the sanitary sewer, and the city warns that discharge running across sidewalks or streets breeds algae in warm weather and ice in freezing weather, leaving the owner responsible for redirecting it.
Snow comes second, and city rules make it a local problem. Snow cleared from driveways and parking lots may not be placed on the street or public right-of-way, and a first violation draws an administrative penalty. With 35.3 inches of normal snowfall, every lot stores its own winter, and every pile melts somewhere. Brine is the third source. Public Works sprays it from 13 trucks ahead of storms, and because de-icers lower the freezing point of water, salty slush at the curb can keep the apron wet on days when plain snow would stay frozen.
- Downspouts that end on or right beside the pavement
- Sump lines that discharge across the drive or the public walk
- Snow piles on the uphill side of the drive
- Lawn or planting beds graded toward the asphalt edge
- A garage slab that sheds water onto the drive
- Gutters that overflow at one corner in heavy rain
Fixes, in the order they pay off
Start with the moves that cost little or nothing. Redirect downspouts and sump lines to the city's 15-foot standard, move the snow pile to the downhill side, and build up any lawn edge that has settled below the pavement so water runs away from it. None of this needs a contractor, and it changes how much water reaches the base before any money goes into the asphalt.
Next, close the pavement. Filling cracks before the median first freeze on October 17 keeps the winter's meltwater out of the till, and the crack filling page covers the materials and timing. Areas that have already failed, the soft spots, birdbaths and alligator-cracked patches, need to be cut out, dug below the wet soil and rebuilt with compacted stone and hot mix, as described under asphalt patching. Sealing comes last, once the water is under control, because a coat over a wet base only hides the trouble.
When a whole drive sits on saturated ground, the lasting answer is a rebuild: excavation, a thicker compacted stone base, grading that sheds water, and in some cases perforated drain pipe in a stone trench along the low edge, the same idea as the farm tile that made the lobe workable. The asphalt paving page covers base depth, the hot-mix season and the permits a new approach needs.
Two local programs can help with the water side of the job. The City of Des Moines' Stormwater BMP Subsidy Program reimburses half the cost of approved practices, including permeable pavers, rain gardens and soil quality restoration, for properties whose stormwater fee account is current, with applications due by June 1, 2028. Urbandale's Storm Water Grant Program covers drain tile to dry a wet backyard. Neither pays for sealing, and both require approval before work starts.
Describe a wet, cracked or sinking drive and send it to independent Polk County contractors.
Quick Answers
How can an owner tell which soil sits under a Des Moines lot?
The quickest route is the USDA's Web Soil Survey, which maps soil series for any area drawn around a property. Field clues help too. Dark, heavy soil in low spots points to Webster or Okoboji ground; water that lingers in the lawn for a day after rain, or a sump pump that runs into late spring, says the same. Clarion ground on a rise drains better but is still saturated at four to six feet from March to June.
Does drain tile work beside a driveway on glacial clay?
It can, and the region's history is the evidence: tile lines are how the lobe's poorly drained farmland became productive. Beside a drive, perforated pipe in a stone trench along the low edge can carry water out of the base, provided the pipe has somewhere lower to go, such as a daylight outlet or, where the city allows, a storm sewer connection. Private lines are not marked by an 811 locate, so any existing tile or sump line should be traced first.
Why does a driveway heave in winter and sink in spring?
Both are the same process. Through the winter, water drawn up through fine-grained till freezes into ice lenses that push the pavement up, most at cracks and edges where water gets in. When the lenses melt, the soil they leave is wetter and weaker than before, and a thawing subgrade loses much of its bearing capacity. Wheel loads then press the pavement down into the soft spot, and each year's cycle leaves the dip a little deeper.
Will the City of Des Moines help pay for drainage fixes on private property?
For some of them. The Stormwater BMP Subsidy Program covers half the cost of approved rain barrels, rain gardens, soil quality restoration, native landscaping, permeable pavers, streambank stabilization and bioretention cells. The property's stormwater fee account must be current, work cannot begin before approval, new developments are excluded, and applications are due by June 1, 2028. Sealing and ordinary asphalt repair are not eligible.
Free Des Moines Quote
Free quote