EG
Civil/Environmental
- Mar 5, 2002
- 20
Hi All,
We have a new commercial building with a BELOW GRADE PARKING GARAGE that is to be served by a new access road running north-south (helps the visual). The parking garage is coming off perpendicular from the access road with a very short spur (garage door will be about 30-ft from edge of access road).
There is a natural drainage channel running along the proposed access road (NOT FEMA mapped/studied...no regulatory flood hazard areas). The drainage is seasonal, but collects a relatively large contributing basin. 100-year flows are around 300 cfs. Using HEC-RAS, we determined the water surface elevations at various points for helping establish site elevations.
Time for the bugger: The site is severely constrained with easements and existing site improvements...leaving us NO ROOM to significantly raise the proposed building, move the building or re-align the access road. I can only specify site grades/walls/berms...
The proposed parking garage is about 5-ft below the 100-year WSEL. Based on the short run of the spur to the parking garage, I need to DIP the access road to make grades work and then rise the access road after the spur intersection. The bottom of the channel, even when dry, does not allow for gravity drainage from the parking garage level.
I plan on using concrete retaining walls along the access road to essentially create a levee that encompasses and limits the area that will drain down to the parking garage. We will need a sound pump system to dewater the drains that collect the runoff that unfortunately terminates at the parking garage door. The concrete site walls will be permanent features rather than berms that landscapers may change over time...
Anyways, does anyone have any experience with such conditions? Any advice other than tell the owner not to move forward?
We have a new commercial building with a BELOW GRADE PARKING GARAGE that is to be served by a new access road running north-south (helps the visual). The parking garage is coming off perpendicular from the access road with a very short spur (garage door will be about 30-ft from edge of access road).
There is a natural drainage channel running along the proposed access road (NOT FEMA mapped/studied...no regulatory flood hazard areas). The drainage is seasonal, but collects a relatively large contributing basin. 100-year flows are around 300 cfs. Using HEC-RAS, we determined the water surface elevations at various points for helping establish site elevations.
Time for the bugger: The site is severely constrained with easements and existing site improvements...leaving us NO ROOM to significantly raise the proposed building, move the building or re-align the access road. I can only specify site grades/walls/berms...
The proposed parking garage is about 5-ft below the 100-year WSEL. Based on the short run of the spur to the parking garage, I need to DIP the access road to make grades work and then rise the access road after the spur intersection. The bottom of the channel, even when dry, does not allow for gravity drainage from the parking garage level.
I plan on using concrete retaining walls along the access road to essentially create a levee that encompasses and limits the area that will drain down to the parking garage. We will need a sound pump system to dewater the drains that collect the runoff that unfortunately terminates at the parking garage door. The concrete site walls will be permanent features rather than berms that landscapers may change over time...
Anyways, does anyone have any experience with such conditions? Any advice other than tell the owner not to move forward?