SURFACE DRAINAGE
By Fred C. Hutchinson, BA, NSLS, CLS

 

Reference to surface drainage as a topic excludes tidal waves, earthquakes and the melting of the polar ice cap.  All, of which, have the capability of flooding a perfectly dry basement.  The topic does, however, try to address the issue of the 100-year storm, building on a flood plain and generally ignoring the laws of nature.

 The “dream home”, no matter the cost or location must take into consideration certain basic rules.  Domestic water is under pressure so delivery from source to dwelling is usually not an issue.  Sanitary and storm sewers from the dwelling are better left to gravity if there is a choice.  Lift stations have a limited capacity during power failures. 

 What many homebuilders and owners are not aware of is upstream water and ground water.  Both can be a blessing as well as a hazard.  If you are to get your water from a well, then ground water is a blessing.  If you build your foundation too low then groundwater becomes your enemy.  Upstream water may be in the form of a trickling brook meandering through your yard on a warm summer day while the same brook becomes a threatening river with April rains and snowmelt.

 There are many property owners who are afraid to leave their homes unattended for fear of sump pump failure.  This applies to areas with municipal services as well as on-site sewer and water.  Actually, the more urbanized properties tend to be at greater risk from surface drainage than rural properties.  The smaller and more compact the development, the less room there is to channel water away from dwellings.  The more developed the area, the more intense the runoff.  The parking lot of the neighborhood mall sheds its water during a rainstorm much faster and with greater velocity than Farmer Brown’s cornfield or a rural woodlot.  The downstream recipient is usually not impressed with poor drainage design.

 Gravity is one of the laws of nature and its effect on water is that it seeks the lowest point in any landscape.  It is important to consider natural sources of water when building a new home.  It is also important to be concerned about the vertical position the foundation and not just its horizontal position on the lot.  Altering your house plans to fit the lot topography is desired over changing the lot to fit your house plans.  Changing a lot’s topography may also have an adverse effect on adjacent land, which could result in liability for damages.

 Many lot owners cut into the rear yard slope in an effort to obtain a nice level backyard.  The result is that ground water becomes a problem and your backyard doesn’t dry out until mid-August.  In an effort to drain the backyard many owners dig a trench to the street and install pipe and gravel (French Drain) that flows year round and in the winter months causes ice damns at curbside and in the street.  If rear yards are sloped and the ground is also sloped away from the foundation, the result will be a surface swale that can handle the water and still be usable by the owner.  The finished landscaped yard should not be less than six inches below the siding and the front yard should slope towards the curb.

 Larger rural properties with on-site services are generally at least five times and often ten times the size of an urban “postage stamp” lot.  Many rural lots have natural features such as brooks, swamps and open ditches that need to be considered when positioning a new home.  Any attempt to alter these features may cause unwanted problem.  The well should always be located at a higher elevation than the septic system and the basement floor should be higher than the septic field to allow a gravity feed.  Lot conditions will sometime require a deviation from the previous suggestion but it is a goal that should be considered.  The homeowner also needs to be ever mindful of low-lying areas that have a history of flooding and make sure that the low price of the lot is a “real deal” and not “real risk”.

 A site plan that shows elevations and all cultural features drawn to scale at the design stage is highly recommended and in some municipalities it is a requirement of the building permit process.  If such a drawing is not prepared then the owner needs to have a good understanding of what is being proposed and the impact of the construction on the finished grade with respect to surface drainage. 

 Building a foundation one foot too high can usually be fixed with a few truck loads of fill while the foundation built one foot too low is entirely a different situation and creates a long-term headache for all concerned.  You should enjoy the sunshine if you take a vacation and not be the least bit concerned about the rainy weather back home.

 

Fred Hutchinson has been the Executive Director of the Association of Nova Scotia Land Surveyors
since 1999 and also is a Past President of the Association.  Mr. Hutchinson was licensed in 1971,
employed by municipal government for nearly six years and spent over twenty-two years in private practice.