Question

You have been assigned the task to complete the preliminary design calculations for the sanitary sewer and drainage system for a new subdivision located just outside of Columbus. The property in question is 1,300 feet (north to south) by 6,500 feet (east to west). The property is very flat (1% average slope). The parcel has been used primarily for agriculture (C=0.40), however, there are 12 acres of delineated wetlands (C=0.05) in the southeast corner of the property. assume the portion of the property that have been delineated wetlands is in the shape of a 45^o-45^o -90^o triangular, with the right angle at the SE corner of the property. The SE corner of the property is also the natural drainage outlet point and there is a channel at that point.

1.Calculate the time of concentration using the FAA Formula; the lowest point on the undeveloped property is as noted above.

2.Calculate the composite runoff coefficient after development if 65 percent of the area will be used for residential units (C=0.60); 15 percent along the south boundary for commercial development (C=0.65); 10 percent street and parking areas (C=0.95); and the remaining 10 percent will remain wetlands or be converted to green space (C=0.15). Calculate the composite runoff coefficient .

Answer 1