Hydrology/Hydraulics
With the design finished, the proposed RDC was applied to the watershed basin seen below:
Pre-Development Hydrology Sub-Basins
Post-Development Hydrolgoy Sub-Basins
Sub-basins 1, 2 and 3 runoffs were not affected by this change due to the placement of the RDC. Sub-basin 4 was slightly changed by the increase of impervious surface such as asphalt, concrete, and riprap in the sub-basin. The asphalt was placed for the convenience of the operation vehicles and was sloped to direct the runoff to the 48” culvert. Sub-basin 5 changed and became composed of a large area of asphalt and some natural terrain. Any runoff collected by sub-basin 5 will drain to the 18” culvert located within sub-basin 5. Sub-basin 6 basically remained the same, majority of the surface is the natural terrain with a small increase of impervious surfaces. The table below contains the details for each of the sub-basins with the new runoffs.
100 Year Event-Pre Development
100 year event – Post Development |
|||||
Sub-basin |
Cf |
C |
i |
A |
Q (cfs) |
1 |
1.25 |
0.21 |
3.96 |
9.46 |
9.83 |
2 |
1.25 |
0.21 |
3.96 |
3.06 |
3.18 |
3 |
1.25 |
0.21 |
3.96 |
9.92 |
10.31 |
4 |
1.25 |
0.35 |
3.96 |
2.77 |
4.56 |
5 |
1.25 |
0.66 |
3.96 |
1.04 |
1.20 |
6 |
1.25 |
0.20 |
3.96 |
1.01 |
1.30 |
∑ = |
30.38 |
||||
100 Year Event-Post Development
100 year event – Post Development |
|||||
Sub-basin |
Cf |
C |
i |
A |
Q (cfs) |
1 |
1.25 |
0.21 |
3.96 |
9.46 |
9.83 |
2 |
1.25 |
0.21 |
3.96 |
3.06 |
3.18 |
3 |
1.25 |
0.21 |
3.96 |
9.92 |
10.31 |
4 |
1.25 |
0.35 |
3.96 |
3.39 |
5.87 |
5 |
1.25 |
0.66 |
3.96 |
0.62 |
2.03 |
6 |
1.25 |
0.20 |
3.96 |
0.82 |
0.81 |
∑ = |
32.03 |
||||
After calculating the new discharge, the overall flow from the basin increased by a total of 5 percent. The tables above, have the calculated runoffs for each sub-basin; for both pre-development and post-development. This increase in runoff was due to the increase in impervious surface. With such a small increase of discharge throughout the basin, the culverts were not needed to be redesigned. With such a small increase in the discharge and the culverts designed for expansion in the landfill, it makes sense that a redesign of the culverts was not needed.