packgrad98
Civil/Environmental
I am reviewing plans submitted by an engineer for a section of a residential subdivision. The development is roughly 5 units per acre in an area that is generally very sandy. The engineer used a "composite" C-value of 0.3 to determine the Q for each inlet. In my experience, the C-value tables have 0.5 for res. lots (5 units/ac) and roughly 0.9 for the paved areas. Based on rough calculations, I came up with a composite C=0.6. Obviously a drastic difference in runoff as well as pipe sizing.
The engineer's argument is that he does a composite for each lot, from side P/L to side P/L and from rear P/L to the C/L of the street. He then determines the amount of impervious area and pervious area within that lot. Using a C-value of 0.1(for lawns in sandy areas on the C table) and 0.9 for impervious areas, he has a composite C=0.36.
My questions are:
1. Is the 0.3 or 0.36 consistant with what others use?
2. Is the C-value listed in the tables for residential lots supposed to already take into account the streets and sidewalks?
3.
The engineer's argument is that he does a composite for each lot, from side P/L to side P/L and from rear P/L to the C/L of the street. He then determines the amount of impervious area and pervious area within that lot. Using a C-value of 0.1(for lawns in sandy areas on the C table) and 0.9 for impervious areas, he has a composite C=0.36.
My questions are:
1. Is the 0.3 or 0.36 consistant with what others use?
2. Is the C-value listed in the tables for residential lots supposed to already take into account the streets and sidewalks?
3.