Hillside lots that have been damaged by fire or are located in a fire-damaged watershed can be susceptible to erosion drainage and runoff/erosion problems. Torrential or prolonged rains cause the most damage. 

To treat surface drainage problems, you will first need to identify the sources of surface water (runoff) flowing onto or over your property. First, walk outside and around your home. As you walk, observe the "lay" of your lot and the surrounding properties. Also, observe your roof and driveway. Is your home on top of a hill where all surface waters drain away from your home? If so, you will be concerned with holding topsoil on your property. Few homeowners live on top of a hill. So, it is more likely that water will flow onto your property from an adjacent hillside. Where will the water concentrate and how can you control the sediment that is carried with the water? 

Gutters and downspouts direct roof runoff

Be sure that your roof is properly fitted with gutters and downspouts (1) that will release water onto a non-erodible surface such as a paved driveway (2). Or you can connect downspouts firmly to solid plastic pipe (3) that will carry water down slope away from your home to a place where it will be released safely such as a paved roadside or storm drain ditch (4). Because twigs, pine needles and leaves can clog gutters and downspouts, the use of gutter guards of 1/4 to 1/2-inch hardware cloth screen is highly recommended. Clear your gutters regularly and inspect them to insure your roof runoff system is working properly. Most homes in New Mexico have foundations situated on sand or silt soils that can settle irregularly when they become saturated and lead to cracking or jamming of windows or doors. It is therefore usually very important to keep runoff from gutter down spouts well away from your house foundation.

Curbs and berms protect sensitive slopes

An asphalt curb, a compacted earth berm, K-Rails, concrete blocks, or other similar structure on the outside edge of a driveway or building pad (5) can direct runoff away from sensitive slopes to an area where it can be released safely. The recommended height of the berm is a minimum of 12-18 inches. (A sandbag berm may be used as a temporary measure.)* A pipe drop (6) may be used to carry runoff down slope to a place where it can be released safely, such as a lined roadside ditch or storm drain.

Lined ditches handle road and driveway runoff 

Roads and driveways can be graded toward a lined ditch or street side gutter designed to handle sheet flow water from paved surfaces and uphill slopes (7 & 8). As shown in the diagram, water from the driveway ditch is released safely into the drainage ditch or storm drain of the main road. At specific intervals along the main road, water may be transported under the road through a culvert (9a) and released safely onto a non-erodible surface. An energy dissipater (9b), such as a rock lined outlet, can serve this purpose where slope is minimal. In steeper areas or where large volumes of water may accumulate, other precautions may be needed to prevent washouts or localized flooding.

Proper grading promotes good drainage

Proper grading of your land helps prevent water from pooling around foundations, flooding basements or below grade structural components, and concentrating water into destructive volumes. In general, grade surfaces flow away from foundations at a minimum grade of 1-2 feet for every 100 feet (10). Grade and compact surfaces evenly since water can collect in depressions or channelize into destructive flows.

Drainage for retaining walls

Good drainage must be provided for solid construction retaining walls (11). Properly placed weepholes and perforated pipe with a gravel backfill behind the wall work well. The small openings between wood boards or non-grouted brick, stone or concrete block retaining walls serve this purpose. Many walls are not designed for saturated soils or ponded water behind them and can break, tip over or slide if this is not prevented with good drainage behind them.

Diversion ditches
A diversion ditch may be needed to handle surface runoff flowing onto your property from upslope. For slopes steeper than 5%, or where large amounts of water are expected, line the ditch with concrete or hand-placed rock underlain with filter fabric or other appropriate measures. Direct water to a safe, non-erodible surface -- never directly onto the downstream slope itself. Always consult a qualified engineer to design water diversion measures.

Maintenance
• Regular maintenance of drainage systems will keep your drainage problems to a minimum. Never direct water onto adjoining property without consulting the owners. Observe your system during the rain when you can watch runoff patterns that affect your property or affect downslope properties.
• Check gutters, downspouts and pipes during and after storms and remove debris that might cause clogging.
• Regularly inspect, clean, and repair berms and ditches as necessary. Signs of over-topping may mean that redesign is necessary or that modifications should be made to handle larger quantities of water. Check for and repair any damage caused by burrowing animals.
• Seed and mulch or otherwise vegetate all bare areas, especially on slopes.
• Regular maintenance saves time and money in the long run.

Safety measures

• Do not start any work until you are assured that both above-ground and underground utility lines will not be affected by your work. Information on the location of underground utility lines can be obtained by calling 1-800-321-ALERT.
• Do not release runoff onto septic leach fields or at the base of structural foundations. 

Inadequate Grading

PROBLEM: If the ground around a foundation is level or slopes toward the house, water is directed into the basement. The soil next to the house is often backfilled without proper compaction and later settles. This is especially true under stoops where water can collect next to the basement wall.

SOLUTION: Place earth around the house so that it slopes away from the foundation wall a minimum of one inch per foot for at least six feet.

Defective or Missing Gutters and Downspouts

PROBLEM: Missing gutters and downspouts cause rainwater to be directed toward the foundation perimeter. A downspout without an extender or splash block is worse than no downspout at all. It is depositing the huge volume of rainwater from the roof in a single concentrated location near the basement.

SOLUTION: Place a minimum of one downspout per 50 linear feet of roof eave. Extensions should discharge water at least four feet beyond the wall. Sloped concrete sidewalks around basements are very effective in directing rain runoff.

Improperly Designed Window Wells PROBLEM: Window wells are like a drain right next to the basement wall. Often they are improperly built so that any water is directed toward, rather than away from the foundation.

SOLUTION: Window wells should be filled from the footing to the window sill with 3/8- to 3/4-inch coarse aggregate. A supplemental drain tile extension should extend from the footing to the base of the window well.

Ineffective Drain Tile and Sump Pit

PROBLEM: Many existing houses simply have no subsurface drainage system. This comes from a time when basements were not used as habitable space. In other cases, the systems do not work for a variety of reasons, such as collapse of the pipe, clogging of the pipe with silt and/or tree roots, or a broken connection to the sump. The sump pit usually contains a pump designed to lift the water to the ground surface outside the foundation wall. This pump can fail.

SOLUTION: See Approaches 2 through 7 that follow.

Improper Drainage with Underslab Ducts

PROBLEM: If heating ducts are installed beneath a basement floor slab, the drainage system may be inappropriately left at a level higher than the duct. In effect, the duct becomes the drainage system, and with standing water within the heating duct, there are potentially serious health consequences from mold contamination.

SOLUTION: Heating ducts placed beneath the basement floor must be insulated, watertight, and sloped to collection points for drainage and cleaning. A drain tile and coarse aggregate can be placed under the ductwork.

Structural Cracks

PROBLEM: Concrete and concrete block foundations usually develop some cracks. They can be severe if floor joists are not properly connected to the foundation wall, thus permitting the wall to move. Also, soil settling causes cracking. Places where walls meet rigid structures like the fireplace often crack as well. Usually, drainage removes the water from cracks, but repair may be necessary.

SOLUTION: Proper footing design and proper connection between the foundation wall and the structure above are required (e.g. anchor bolts or straps at the sill plate and floor joists nailed to the sill plate).

APPROACH 1:
Install Proper Gutters and Downspouts and Correct Grading

A great number of basement water problems can be solved by handling rainwater and surface drainage properly using gutters and downspouts with extenders or splash blocks to carry the water away from the foundation. Sloping the grade away from the house, which may require hauling fill to the site, is very important. This should be done before any below-grade drainage system is installed, since the above-grade corrections may solve the problem. Even if a drainage system is required, removing water at the source as much as possible is necessary.

APPROACH 2:
Exterior Drainage System

Installing an exterior drainage system at an existing building is the most costly, but also the most effective water control approach. This requires digging up the area around the foundation and rebuilding it similar to a new house installation. It also requires digging up shrubs and other obstacles around the house.

Usually, waterproofing and insulation are installed at the same time, in addition to making any repairs to the structure. The traditional exterior drainage systems use free-draining sand in the backfill. Drain tile can be placed beside or on top of the footing. Level drain pipe installations are satisfactory. A minimum of 12 inches of coarse aggregate should be placed around the drain tile.

Free-draining Membrane or Board

It can be expensive to haul pea rock or sand to a site for backfilling purposes. Instead, a drainage mat can be placed against the foundation wall and then backfilled with any soil on site. The drainage must have a free-flowing path to the perforated drain pipe below.

Draining to a Sump
All exterior drainage systems must drain to a sump that can be pumped out. The sump must have an airtight, childproof cover.

APPROACH 3:
Interior Drainage Channel above the Concrete Slab

In most cases when water is entering the basement, an interior drainage system is installed. The simplest and least costly approach is a drainage channel adhered at the base of the wall and the floor slab. Water is collected and drained into a sump using another channel placed on top of the slab, then through a trap to the sump basin. The sump should have an airtight, childproof cover. This system is best suited to a concrete wall with cracks. It does not solve the problem in masonry walls because water remains in the block cores at floor level and the water level is only lowered to the top of the slab. With this approach, the water is not completely removed from the space. The result is that humidity, mold, and mildew can still be a problem. This system cannot drain groundwater from under the floor slab.

APPROACH 4:
Interior Drainage Channel within the Slab Edge

Another technique is to place a drainage channel at the base of the wall on top of the footing. This requires removing and then replacing the concrete along the slab edge. The drainage channel is connected to a drain pipe leading to the sump. The sump should have an airtight, childproof cover. This approach is effective for concrete masonry walls with water problems because it drains the block cores completely. Holes must be drilled at the base of every block core to permit drainage. This may require removing more than the minimum amount of concrete, as shown, to fit the drill in. These systems have different shapes and prices depending on the product installed. Because moisture is allowed to penetrate the block cores, it is essential to cap the tops and place an air-vapor barrier on the wall.

APPROACH 5:
Interior Drainage System Beneath the Slab

The most effective of the interior drainage systems is a perforated drain pipe installed inside the perimeter of the footing. This requires removing and replacing concrete at the slab edge. By placing the drain pipe beneath the slab, it drains the area to a lower level. Similar to an exterior system, the drainage pipe connects to a sump. The sump should have an airtight, childproof cover. A critical component of this approach is the dimpled plastic sheeting placed at the base of the wall and beneath the slab edge. Dimpled sheeting is similar to a small egg crate and permits free drainage down the wall and across into the drain pipe. It is less expensive than many specialized drainage channel systems. In low permeability soils, this system cannot accept rising groundwater unless there is an aggregate layer under the slab.

APPROACH 6:
Finishing a Basement with Moisture Problems

Using the interior drainage system shown above in Approach 5, one method of finishing the space is shown at right. A polyethylene vapor retarder is placed over the foundation wall before installing finishes. No interior vapor retarder should be placed over batt insulation when finishing walls if there is already a vapor retarder on the foundation walls. There should be an interior air barrier (such as the wall finish material) sealed at the top and bottom plates and at all penetrations. Rigid insulation is placed on the floor and then covered with a decay-resistant plywood sub floor.

Another approach to making the basement dry for interior finishing follows.