Water is probably the most important aspect of any landscaping project. When it's managed properly it can silently keep your yard lush and green but when more often than not it's not addressed properly it becomes a nightmare! There are three primary methods of water management. The first being surface drainage, the second being sub surface and the third is moisture barriers.
One of the easiest to get wrong is the slope. "just slope it away from the house" It seems pretty easy! But without the proper tools, equipment and training surface drainage is the biggest problem. In order to get proper drainage the surface needs to have a 2% slope. Now in theory that sounds great but in practice especially in urban areas that's not possible. A 2% slope is 1" drop over 4 feet. It should be a fairly noticeable incline just walking over it. Lesser slopes may still drain but any small bumps or ridges will be much more likely to slow or stop water. In grass especially anything less than 2% the water will slow down considerably and will soak in rather than flow down. This will give you a soft easy to damage surface and takes much longer to dry out.
When a 2% slope is not practical or there is a poor quality basement foundation or a large volume of water subsurface drainage is the answer. Subsurface piping is still effective at .5% grade as well it prevents surface erosion. Also if done properly it can wick water out of the subsurface soil and carry it away. In residential applications the most commonly used subsurface pipe is Big "O" or weeping tile. The black corrugated 4" pipe you often see coming through retaining walls and coming up to connect to your downspouts. The primary benefit of Big "O" is that it's cheap and easy to install. It also comes perforated with a filter cloth already installed. But it has several very big drawbacks. Firstly and most commonly it have very little crush resistance. 99% of these pipes that are removed from yards are crushed flat in several places. The second drawback is the corrugated interior allows debris and ice to build up easily and makes it very difficult to remove. This helps compromise the structure leading to collapse.
I only use the perforated pipe in short lengths to wick water into a primary PVC pipe to be carried away. Although more difficult to install than a single corrugated pipe a trunk and branch type arrangement will last much longer and will still perform even if all the perforated branches collapse. For carrying water especially large volumes from down spouts or drain grates i will only use PVC pipe. PVC being rigid is much easier to grade for proper slope and can handle substantially more abuse. I did a test this summer using a 4" PVC drain pipe I laid across the driveway. On top of the pipe I put 4" of clean clay and packed it down with the excavator tracks. I then had a fully loaded dump truck drive over it around 20 times. The pipe maintained its shape and carried the storm water from the street under my worksite for the entire month then was still in perfect shape after being dug out with the excavator teeth.
In comparison Big "O" will collapse with a couple rocks or wet soil and PVC wont collapse with tens of thousands of pounds driven directly over top.
The last are of water management is moisture barriers. The two primary applications are to keep your house and foundation dry or to keep water from a aquascape feature from leaking out. Most of the homes in calgary did not have water management systems installed under the foundations. Although its code in most of canada for some reason Calgary builders were given the option. What this means is that once water inevitably gets past the soft backfill to the bottom of your foundation wall and into the gravel base it has nowhere to go. It then leaches through the concrete or leaks through the cracks damaging your basement finish or breeding mold. Most of these problems can be fixed with the proper installation of a sump pump in the basement. More severe cases may require digging around the foundation to install perforated drain pipe and a moisture barrier against the concrete. The perforated pipe needs to be backfilled with wash rock and drained into a pit containing several yards of wash rock to collect and disperse the water away from the house. The moisture membrane needs to adhere to the foundation and extend up past the grade to the siding flashing. This presents a problem for the roll on or membrane systems as the foundation is usually very dirty and rough and can be very difficult and time consuming to clean enough to get a good seal. We have found the best product is urethane foam. When sprayed on it adheres very well to the concrete wood and flashing creating a single solid seal as well as providing R-Value to the foundation. It is also much less likely to get damaged when backfilling. This foam can also be sprayed on the inside of the foundation wall at significantly less cost.
When facing a water problem or when considering a landscaping contractor ask them what materials they use and how they plan to address the potential problems with each material. And if you have had landscaping done in recent years and the landscaper installed Big "O" and it has not been cleaned out seasonally it is very likely clogged or crushed. And if your landscaper drove any sort of equipment in close proximity to the pipe it is guaranteed to be crushed. Furthermore if the pipe was installed in wet or saturated conditions chances are slim that it survived. We have thermal cameras and cable cameras that can inspect your drainage lines to see if they are still intact. You will want to have it checked and cleaned before spring runoff and before your landscape warranty runs out if any.
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Water is probably the most important aspect of any landscaping project. When it's managed properly it can silently keep your yard lush and green but w...