One area, behind the association manager's townhouse, consisted of an approximately 20-ft diameter depression where stormwater ponds for days following a rainstorm. The problem at this location is compounded by what appears to be a sanitary sewer manhole with the top that was set too low in the ground. The drainage way through this area was very poorly formed with high spots and low spots at random. It appears that the rough grading in the area was simply seeded in its present condition without any manicuring of the grading to force drainage to the area drop inlets. The nearest storm drop inlet downstream from this area was sitting too high for the drainage area and as a result the topsoil around the inlet was very wet and mud due to ponding. Two recommendations for this area are; first, to raise the top of the sanitary sewer manhole about 12" to allow filling of the depressed area; and second, to neatly finish grade the area and fill the depressed areas, forming accurately flowing stormwater runoff to the nearest inlet.
Another area that exists between the townhouse property and the adjacent property consists of a 6-ft high cut of grade separation to the neighboring subdivision. Part of the slope has been filled with erosion control fabric to get a good stand of grass to form on the slope. The bottom of the slope near the wood fence has a series of storm drop inlets to collect the storm runoff. At the time of my visit, approximately 4-inches of standing water could be observed near the fence. This location possibly should have been constructed with a keystone type retaining wall which would have allowed for a wider drainage swale to be formed to force stormwater runoff to the nearest storm drop inlet. If the swale were cut any deeper into the slope, erosion would probably be the result, and if the swale were raised, it could possibly result in standing water occurring inside the townhouse fence.
The last area which I observed was standing water at the curb of the parking lot driveway near the entrance to the townhouse property. I understand that this location was the dividing line between two developments, that was constructed by two separate contractors, and now is commonly owned by the association. It appeared that the first contractor formed the upper parking lot with a steeper grade on the final section of curb and gutter than should have been formed. The second contractor set curb and gutter higher than would allow the drainage to continue, and as a result, it appears that about 10-ft of ponding occurs at each side of the driveway. An approximately 3-ft wide by 15-ft long by 2-inch deep area of standing water was notable on the west side of the roadway at the time of my visit. It was apparent that the ponding on east side had just recently subsided. This condition is referred to as a sag in the curb and gutter and the best solution would be to construct curb drop inlets on each side of the driveway. It appears that a storm drainage pipe passes beneath the sag area noting the locations of the storm drop inlets in the grass beyond the curb. Ideally, the construction of two curb drop inlets could be built over the top of the drainage pipes without disturbance of the asphalt pavement. Additional removal and replacement of curb and gutter and pavement may be necessary to force the drainage to curb drop inlets if the sag is not exactly over top of the storm pipe beneath. In my estimation, this location is most likely the most costly condition to correct due to the need to construct the curb drop inlets. An alternative for the east edge of the driveway would be to break open the curb at the lowest point, and form a drainage ditch across the grass towards the natural area and force drainage away from the pavement. The appearance of this alternative would be less desirable than the formation of the curb drop inlet, and it would only drain the east side of the driveway, not the west side.
Another area I observed a drainage swale that curved around the end of a townhouse unit and behind the unit towards a storm drop inlet at the rear of the townhouse and adjacent to a power company transformer. The swale had about 6-inches of standing water at the time. Again at this area, it appeared that the finish grading of the swale was not accurately completed, and as a result, the drainage swale is too low. It appeared that the swale should be raised about 6 to 12-inches which would force drainage towards the storm drop inlet. At the inlet, the electric transformer was very close to the drop inlet, and as a result, the subgrade for the pad of the transformer was beginning to erode away and expose the underside of the pad. One recommendation to correct this would be to form 2 or 3 rows of keystone type retention blocks against the transformer pad to prevent the soil erosion from occuring.
Another area I observed adjacent to the wood fence dividing the townhouse property from the adjacent development had about 6 to 8-inches of standing water for about 100-ft upstream of the nearest storm drop inlet. This appeared to be the result of a poorly formed drainage swale that should have been formed about 8 to 12-inches higher. At another very similar location, a 6-inch deep by 12-inch wide eroded drainage way had formed and was full of water. My recommendation for this area is to raise the drainage way to force drainage to the inlet and provide some excelsior type erosion control matting to prevent erosion while a suitable stand of
grass can be grown in the channel.
grass can be grown in the channel.
There was one area that I observed where the sidewalk was about 2-ft away and 2-ft above the adjacent storm drop inlet. Erosion control fabric had been placed along the slope for about 10-ft between the two, however, it did not appear that the repair would last long before the steep slope would erode away. This area would benefit from about 3 to 4 rows of keystone blocks that would protect the soil from eroding away from the sidewalk.
One area adjacent to the end of a townhouse row, consisted of a well graded wetland area extending from the natural area towards the storm drop inlet. The wetland area had about 4-inches of standing water extending 50-ft upgrade from the inlet. Here, my recommendation would be to extend the natural vegetation of the natural area to encompass this area, and not to cut the grass.
Another area that exists between the townhouse property and the adjacent property consists of a 6-ft high cut of grade separation to the neighboring subdivision. Part of the slope has been filled with erosion control fabric to get a good stand of grass to form on the slope. The bottom of the slope near the wood fence has a series of storm drop inlets to collect the storm runoff. At the time of my visit, approximately 4-inches of standing water could be observed near the fence. This location possibly should have been constructed with a keystone type retaining wall which would have allowed for a wider drainage swale to be formed to force stormwater runoff to the nearest storm drop inlet. If the swale were cut any deeper into the slope, erosion would probably be the result, and if the swale were raised, it could possibly result in standing water occurring inside the townhouse fence.
The last area which I observed was standing water at the curb of the parking lot driveway near the entrance to the townhouse property. I understand that this location was the dividing line between two developments, that was constructed by two separate contractors, and now is commonly owned by the association. It appeared that the first contractor formed the upper parking lot with a steeper grade on the final section of curb and gutter than should have been formed. The second contractor set curb and gutter higher than would allow the drainage to continue, and as a result, it appears that about 10-ft of ponding occurs at each side of the driveway. An approximately 3-ft wide by 15-ft long by 2-inch deep area of standing water was notable on the west side of the roadway at the time of my visit. It was apparent that the ponding on east side had just recently subsided. This condition is referred to as a sag in the curb and gutter and the best solution would be to construct curb drop inlets on each side of the driveway. It appears that a storm drainage pipe passes beneath the sag area noting the locations of the storm drop inlets in the grass beyond the curb. Ideally, the construction of two curb drop inlets could be built over the top of the drainage pipes without disturbance of the asphalt pavement. Additional removal and replacement of curb and gutter and pavement may be necessary to force the drainage to curb drop inlets if the sag is not exactly over top of the storm pipe beneath. In my estimation, this location is most likely the most costly condition to correct due to the need to construct the curb drop inlets. An alternative for the east edge of the driveway would be to break open the curb at the lowest point, and form a drainage ditch across the grass towards the natural area and force drainage away from the pavement. The appearance of this alternative would be less desirable than the formation of the curb drop inlet, and it would only drain the east side of the driveway, not the west side.
