HomeMy WebLinkAboutFloodwayBleyl & Associates
Project Engineering & Management
October 16, 2007
Alan Gibbs, P .E.
Development Engineer
Planning and Development Services Department
P.O. Box 9960
City of College Station, TX 77840
Re: REMAX East University Drive Office Building
Floodway Determination
Dear Alan,
1 722 Broadmoor
Suite 210
Bryan, TX 77802
If you recall, we met on 9/19 to discuss the relative impacts of the Carters Creek
Floodway on the small commercial parcel located on the south side of University Drive
East just west of Veterans Park. Based on those discussion, and subsequent field survey
information, we are providing the following determination as to the current location of
the floodway with respect to this site.
Exhibit A is a copy of the current FIRM panel, with the project site located by scaling
from the nearest city limit line comer. It can be seen that the FIS cross section H lies
directly across the site.
Exhibit B is a copy from the current Flood Insurance Study which includes the river
station of cross section Hof 12.39, and the calculated floodway width at this cross
section to be 1482ft.
Exhibit C is a copy of the 1979 HEC 2 printout used to create the Flood Insurance Study.
On page 6 ofthis exhibit is the input card for the section at river mile 12.39, which we
know from the FIS is cross section H. From this input card we see that the cross section
station of the east high bank is 4300, the cross section station of the stream centerline is
4327, and the cross section station of the east high bank is 4372.
On page 15 of Exhibit C, we find the floodway determination output from the HEC-2
analysis. This indicates that the eastern limit of the floodway is at cross section station
2890, the western limit of the floodway is at cross section station 4372, and that the
resulting floodway width is 1482 ft.
Using the stream centerline station of 4327, and the eastern floodway limit station of
2890, we can obtain the distance from the centerline to the eastern floodway limit of 1437
ft.
Bryan
(979)-268-1125
(979)-260-3849
Austin
(512)-328-7878
(512)-328-7884 Fax
Conroe
(936)-441-7833
(936)-760-3833 Fax
This month, our client authorized Kerr Surveying to provide additional data per our
discussions. Using the same survey datum as was used in the site boundary survey
preparation, the surveyors picked up the current east and west high bank coordinates at
the actual location of FIS cross section H as verified by myself in the field.
Conclusions:
Using the FIRM, FIS and effective HEC-2 model currently in effect, we have determined
the distance from the stream centerline to the eastern floodway limit at the subject project
location to be 1437 ft.
Using field information provided by Kerr Surveying, we have tied the current stream
location to the actual property comers to precisely relate the two features. At Section H,
the distance from the current stream centerline to the nearest property comer is 1486.64
ft. By comparing the eastern floodway offset with this dimension, it should be clear that
the floodway limit is almost 50 feet away from the property line.
At the next cross section upstream, roughly 1900 feet away, the eastern floodway
distance has increased by only 85 feet, or about 4.5 feet per hundred feet of stream
length. Since the property is only 248 feet deep, that would equate to about 11 feet of
additional floodway width.
Since Carters Creek is roughly parallel with the property line of the subject site at this
location, we contend that while the floodway is appx. 50 feet from the property's
southern comer, it may be as close as 39 feet to the western comer. Either way, the
floodway does not reach the site.
Therefore, since this information is currently in effect, and supports the position that
there is not floodway on the subject tract, we conclude that the development should be
allowed to proceed in accordance with the City's Flood Hazard Mitigation Ordinance,
whereby encroachments may be allowed into the flood fringe.
We remain ready to discuss this information or any concerns you may have at your
convenience.
Cc: Tim Ware, REMAX