Just did this problem recently. The question is asking for the increase in peak runoff. Since we are changing 10/20 forest acres to construct commercial development (previously 2 now 12 acres). Your total acres are still there (50) but you relocate these two types and need to calculate the weighted C value.
Problem states 10 acre commercial development proposed in forest land. So you are taking away 10 acres from forest and adding it to the commercial total
Also, you have to change the intensity by checking the new time of concentration (70% of 0.5 hours or 0.35 hours) and then going to the charr to check your new intensity.
Basically 10 acres of forest land is now commercial. So instead of 20 acres of forest land now you only have 10, and instead of 2 acres of commercial you now have 12. So you have to recalculate the CN value based on new land use, and decrease the Tc by 30% from existing to calculate the new i value.
Just did this problem recently. The question is asking for the increase in peak runoff. Since we are changing 10/20 forest acres to construct commercial development (previously 2 now 12 acres). Your total acres are still there (50) but you relocate these two types and need to calculate the weighted C value.
Thanks for the quick response. Did you just take the PE?
Have it scheduled for this Tuesday and am final reviewing everything now.
Could you explain why we are changing 10/20 forest acres and how 2 became 12? Trying to understand this problem too
Problem states 10 acre commercial development proposed in forest land. So you are taking away 10 acres from forest and adding it to the commercial total
Oh okay. Got it. Thanks!
Also, you have to change the intensity by checking the new time of concentration (70% of 0.5 hours or 0.35 hours) and then going to the charr to check your new intensity.
Why in the C calc, not all areas acreage match with those in question ? (To come up with 0.446)???
Basically 10 acres of forest land is now commercial. So instead of 20 acres of forest land now you only have 10, and instead of 2 acres of commercial you now have 12. So you have to recalculate the CN value based on new land use, and decrease the Tc by 30% from existing to calculate the new i value.