Residential ground surface storm drain systems must transport excess moisture away from designated areas where excess water would otherwise prevent the traditional use of a residential property. If rainfall is permitted to pond or collect next to a structure built on expansive soil, the structure could also be afflicted by unscheduled distress brought on by swelling bearing soils because of increased soil moisture content.
Likewise, perpetually moist ground surfaces limit recreational using residential yard areas, and could become a breeding ground for disease carrying insect infestations. Water must freely exit the property to assure unrestricted, healthy, and environmentally safe using land areas within residential property boundaries.
Drainage Improvement Guidelines and Criteria.
Install a Roof Rain Gutter System. Uncontrolled roof rainfall runoff can erode the bottom surface along the inspiration perimeter and provide a source of excessive and non-uniform water input to the inspiration perimeter beam bearing soils. Variances in bearing soil moisture content distribution along the inspiration perimeter may end up in unscheduled foundation system vertical displacement and rotational movement.
Rain gutters and downspouts ought to be placed along the whole house perimeter eave lines in which the sloping roof line discharges rainfall runoff. The gutters will capture and convey roof rainfall runoff into downspouts. The runoff is then discharges onto the ground surface swale, or right into a subsurface solid pipe drain system. This type of gutter system can help to stop ground surface erosion and stop excess water accumulations near the inspiration system.
- Improve or Modify Existing Ground Surface System (ASCE, section 7.35). The following criteria may be applied to enhance or modify the prevailing ground surface drainage system:
- Surface Grading along the Foundation perimeter. A minimum slope of 5% (6″ fall per 10′) away from the foundation perimeter should be provided for adjacent ground areas.
- Ground surface swales parallel to the house walls (rear yard and both side yards) shall have longitudinal slopes of at least 2% (6″ per 25′) if practical, and 1% (3″ per 25′) minimum.
- Eroded surfaces should get replaced with vegetated surfaces.
- Gaps between concrete surfaces along the inspiration system perimeter that allow surface water to infiltrate into the inspiration bearing soils ought to be eliminated.
- Concrete surfaces which will allow water to flow towards the foundation system perimeter should be modified to direct water away from the foundation perimeter.
- Erosion Control. Ground cover ought to be placed in areas where ground surface erosion currently exists.
- Surface Water Drainage Option A. The ground surface should be graded to slope to a number of subsurface solid drainpipe (plastic or PVC) single collector inlets or continuous grate type rectangular inlets.
The drain inlets ought to be located to empty excess water a little distance from side and rear yards and discharge to sunlight in the front yard. The road serves as the drain outfall where storm water is directed into street gutter inlets. Cleanouts should be provided at 50 feet intervals for correct maintenance. Roof rainfall gutter downspouts could also be connected to the subsurface solid pipe system provided the pipe has sufficient ability to prevent a backwater condition. The pipe must have no less than slope of 1% as well as the daylight discharge. In any case, the ground surface slope along the inspiration perimeter must comply with local building code requirements.
Subsurface Water Drainage Option B.
Subsurface water drains are appropriate to control surface water runoff. They could consist of a perforated pipe placed in an aggregate filled trench (“French Drain”) together with an optional filter fabric to stop pipe stoppages. The pipe should have no less than slope of 1% as well as the surface outfall. Cleanouts should be provided at 50 feet intervals for maintenance. In any scenario, the ground surface slope along the inspiration perimeter must comply with local code requirements. Gutter downspouts should not be connected to a perforated pipe system.
Monitor foundation performance after completing drainage improvement measures to guarantee their satisfactory implementation.
Recommended drainage improvements, including Option A and Option B above respond to the requirements of section 5.8 “Remediation Criteria” whatever the ASCE Guidelines and doesn’t constitute an engineering or construction design document. The above guidelines and criteria are for planning and pricing purposes and they need an on-site civil survey and geo-technical evaluation at the time the hard work is done.