Drainage Solutions, Simple Storm Water Management and Landscape EngineeringJanuary 24, 2019
Look at how water flows over, through and into your property and landscape. This observation is especially valuable during storm events. Consider the source: uphill, adjacent property, etc..
Sometimes even when we have substantial drainage systems, we need to reevaluate the function of drainage due to changes in the landscape environment. This may be caused by changes in the hydrology of the watershed above or below ground. During this past year we have seen issues that under normal circumstances may not be a problem. When the ground water table is high and the ground is saturated, existing piping and catch basins may be temporarily unable to handle a large volume of flow.
In this case, our client had a small amount of water at the base of the inside basement wall. Upon a proper inspection of the grounds we found the following: property was at significantly lower elevation from neighbors properties, patio had settled, pitching toward rear of house, window well covers broken, neighbors’ gutters and leaders were discharging towards side of house (where the problem occurs), lack of perimeter drain, bioswale and grade/pitch incorrect, evidence of significant loss of topsoil, scouring/erosion. The rear yard was very shady, mostly overgrown trees and shrubs, above the retaining wall. This reduced evapotranspiration, keeping the heavy clay soil damp. Additionally, the window well where the problem occurs happens to have a valve box for irrigation located very close.
The first step was to examine the property survey which showed the location of three cultec dry-wells cultec.com as well as piping and catch basins. For technical support we utilize conservationtechnology.com & ndspro.com. To correct the issues we started by tree removal and severe pruning to alleviate the deep shade. Next we excavated to expose the exterior foundation wall to the interior floor depth to be sure the foundation was not compromised by cracks/intrusion. We checked the irrigation system for leaks. We re-graded (by elevating) the side and part of the rear yard/lawn to increase pitch and volume of the bioswale. The installation of the cultec dry-wells were appropriately located, however, they were installed too deep considering the impervious clay fill between the surface and top of system. As a result, the water poured over the retaining wall (which also lacked proper drainage/weep holes), failed to infiltrate to the subsurface dry-wells, and flowed to the rear and side of house.
This drainage problem was remedied by installing a perimeter drain (perforated PVC/gravel/filter fabric) at the base of the retaining wall at a depth of 18”, the top void filled and re-graded with a topsoil/compost mix to increase storm water infiltration. Most importantly, we connected the perimeter drain to the deep cultecs by means of a vertical infiltration trench (gravel). While we were at it, we also prepped the ground for the new play set by dethatching the grass, de-compacting the ground/surface by hand, installing filter fabric and playground mulch (cedar chips) for under the playground surface.
As part of the scope of work we also: core aerated the lawn, applied gypsum, compost, topsoil, seed accelerator, re-graded and seeded the rear and side lawn (with 13 improved grass varieties/species) including the bioswale. We installed new window well covers and repositioned existing unused bluestone pieces to create a walk to the play set.
Once complete, even without re-pitching the rear patio, which remained slightly sunk below grade, the water intrusion in the basement was remedied. The total project took three full days. The visual effect was a dramatic improvement. The functionality was equally dramatic as the children were able to use the play set and rear lawn right away, even though it was getting rather late in the fall (Halloween).
President, Landscape Ecologist