HomeMy WebLinkAboutMiscellaneousCOLLEGE STATI
P. O. Box 9960 1101 Texas Avenue College Station, TX 77842
Tel: 409 764 3500
The Wallace Group, Inc.
P.O Box 22007
Waco, Texas 76702
Attn: Mr.. George E. Walker, Jr., P.E.
c% Tony Tomchesson
RE: City of College Station. Business Park and Pebble Creek Development
Corporation Drainage Study
Dear Mr. Walker:
In reference to the above project, we have reviewed the drainage report and have several comments.
In the report you indicate that with the development of 233.34 acres in Pebble .Creek, south of
Spearman Drive, and other development in the area, that there will be an increase in water surface
elevation in Alum Creek, Stream AC-1. Given this, your recommendation is not to require
detention for Pebble. Creek in this area. Instead, you recommend cleaning the channel section of
underbrush, thereby. reducing the Manning's "n" and dedicating a drainage easement. that will
contain the fully-developed I00-year floodpiain. With this cleaning, you show only a slight (0.05')
increase in water surface elevation. While we understand your recommendation a~there are
several points we would like to add.
1. Since there will not be detention for Pebble .Creek, it is imperative that the :improved
Mannng's "n" value be maintained so as to assure no future increase in water surface
elevation. In order to maintain those improved "n" values, there will need to be adequate
access to the creek for cleaning equipment as well as assurances that no impediments will
occur within the 100-year floodplain. We have reservations regarding maintaining a
decreased "n" value when the improvements are merely decreased vegetation. It is difficult
to assure that maintenance schedules will be adequate to accommodate this in the future.
2. In the.:report you state that the Ciry of College. Station. Drainage ordinance allows. a one foot
rise in the 100 year water surface elevations. This statement is not totally correct.. The
College Station Ordinance states "When a regulatory floodway has not been designated, no
new construction, substantial improvements, or other development, including fill, shall be;
permitted within zones. designated Al-A30 and AE on the Community's FIRM, unless it is
demonstrated that the cumulative effect of the proposed development, when combined with
all other existing and anticipated development, will not increase the water surface elevation
ofthe base flood more than one foot at any point within the community." Stream AC-1 is
defined on the FEMA FIRM as AE with no floodway determined.
3. The .best way to assure that fences or other impediments to flow are reduced ornon-existent
within,this floodplain is to either dedicate the fully-developed 100 year floodplain in either a
dedicated right-of--way (wherein the city would be the maintenance entity) or common area.
(wherein the developer or a homeowner's association would be the maintenance entity). In
Home of Texas A&M University
Apri19, 1998
the case of a drainage easement where individual lot owners have property ownership of a
portion of the floodplain, they usually desire to fence their property. We recommend the
dedication of aright-of--way or common area.
4. With regard to your table on financial responsibilities for the cleaning, the City certainly
cannot. commit other property owners to participation. As for City participation, in
discussions with Elrey Ash, Economic: Development Director, any participation would have
to receive council approval.
Your analysis currently assumes all properties in the. Business Center will not detain. Some
of the Business Center individual properties will be detaining on-site. You may wish to
rerun your analysis to accurately identify the post .development runoff rate entering Stream
AC-1 considering some detention within the :business park, as well as identify the revised
amount of financial responsibility for each property owner.
6. In looking at other hydrologic reports for Stream AC-1, it appears FEMA flows may be
conservative. Although you .can use the FEMA flows. for your analysis, you may wish to
revise ppour hydrology if you ,agree that the numbers may be high. Keep in mind that this
Q'Q i r~
would ~+~~ the necessary FEMA map revisions to'be submitted. You may decide this is
beneficial or not.
We would like for you. to consider an alternative plan given the above 6 points. Please call if you
hav~any questions. We look forward to hearing from you in the near future.
Veronica J. B~ Morg.
Assistant City Engmee
~Z~
W. Paul Kasp
Graduate Engineer
xc: Elrey Ash,. P.E., Director of Economic. Development
Jim Callaway, Director of Development Services
Mark Smith, P.E., Director of Public Works & Acting City Engineer
Shirley Volk, Development Coordinator
Joel Mitchell, P.E., McClure Engineering
FILE NOTE
Pebble .Creek Phase 8C
Case #98-224 & 98-334
I spoke with Jed Walker of The.Wallace Group and informed him that any future subdivisions in Pebble
Creek would need to be preliminary platted. At a predevelopment meeting, we discussed the passibility
of going straight to final. plat on Phase 8G from the Master Plan tha# was approved in July of 1998. At
that time, they provided us with a master utility plan for the subdivision in order to get Phases 8A and
8B approved. We agreed to go o final plat on these two .phases only. Any subsequent. plats after SA
and 8B must include a preliminary. plat followed by a final. plat. (We will process Phase 8B as a final
plat without a preliminary since. that's what as agreed to previously
Development Coordinator
June 22, 1.999