DR9303-CS 930127To: Alan D. Ratliff, City Manager
From: Kenneth M. Griffin, P.E., City Engineer
RE: Barbara Austin Drainage Problem
Date: January 27, 1993 ~ x.~ ,.~
As you may be aware, Ms. Austin has recently processed a zoning requestSthrough the Planning
and Zoning Commission. It appears a~ Rough she is in the process of getting ready to develop
her property,in the near futurc. There',has been some conversationsabout the money set aside
by Council in last year's budget to address the drainage concerns at the intersection of Moore
Road and Sandy Lake Road. Because it appears that this project is about to take off, I have
revisited the drainage concerns at the intersection to try and ascertain what participation, if ang,
the City should have in the ultimate drainage solution.
There are two ways to look at the City's particip~t~?~n i.n the drainage solution. One would be
to look at the drainage basin that has always draine~C~'~.~'Austin's property and then to ascertain
whether or not those drainage patterns_were changed during the development of the property
south of Sandy Lake, ~ Y.f m~, t"~e ~tC~y could participate in the percentage of difference of
change. In this particular case, it appears as though the area draining through Ms. Austin's
property from the south/prior tol~evelopment of the property~the south)was approximately
65 acres. This determination is based on USGS topography information flo&n in 1956 and field
checked in 1959.~~on the drainage area map for Moore Road, currently there are
approximately 80 acres of land draining through Ms. Austin's property from the south. Th~
difference in the two drainage areas appears to be the area where the Austin Elementary and Fire
Station No. 2 are located. From the original contour maps it appears as though that area should
~ .
have drained south, ~~lunng the development of the property it was taken to Moore Road
into a storm drain system and then discharged north.
If you use this option to figure the City's percentaee._ vpu would take the. a, pproximately 15 acres
that have been rerouted ~d compare ~t to the ~-~, -80-acres that eu~'~' drm~hrough Ms.
Austin's property. Th'~ would yield a change in area of ~. Therefore, the City's
participation in the solution would be 1:,~.~.~%.
The second alternative would be to look at the actual amount of water that drained through Ms.
Austin's property prior to the development and compare it to the amount of water that currently
drains through Ms. Austin's property. As previously mentioned, there were approximately 65
acres south of Sandy Lake that drained through Ms. Austin's property. The runoff from that
property./in an undeveloped statejwould be approximately 164 cfs. Also, prior to gt~
eonaruetion of any roads north of Sandy Lake, there were about nine acres of land that drained
through Ms. Austin's property. ThO"came from west and east of her property prior to the
developmemt of Moore Road to the west of her property and Food Lion to the east of her
property. ThY nme acres contribute} an additional 23 cfs for a total undeveloped flow through
Ms. Austin's property of approximately 187 cfs. 2d~, ~.s previously mentioned, there ~
about 80 acres of developed property that currenfly drains through Ms. Austin's property. Th~*'~
80 acres generate/a runoff of approximately 345 cfs. To get the percentage of the City's share,
you take the 187 cfs as a percentage of the 345 cfs. That percentage yields 54.2%. This means
that of the water currently draining through her property, 54.2% of that water drained through
her property prior to deve~pment. Therefore, the City's participation under this scenario would
only be the increase in thlil runoff, i.e, 45.8%.
The Albert Halff study shows a preliminary design for this solution that includes a 66 inch RCP
for Moore Road north to the existing open channel on the west side of Moore Road by the
apartments. The Albert Halff study also assigns an estimated cost of $249,000 to that drainage
system. My calculations, including Engineering costs, show the construction cost to be in the
neighborhood of S240,000. Using the $240,000 sum, under option number 1, the City's
participation cost would be $45,000 (.1875 x $240,000). Under option number 2, the City's
participation cost would be $I10,000 (.4550 x $240,000). As yo.~t can see, depending upon
which way the City wishes to approach the solution to this problem~ould more than double the
City's participation in the solution.
I am unsure which direction Council would wish to pursue on this option. However, as I
previously stated at the July 28, 1992 City Council meeting, developers typically construct
improvements through their property to handle any off-site drainage in a developed condition
that drains through their property. The subdivisions I pointed to were the Conneil Skaggs (10
x 8 box culvert, 99 acres off-site), Park Place (27 and 42 inch RCP, 38 acres off-site), Country
Estates (54 and 16 inch RCP, 27 acres off-site), Pecan Valley (24 and 33 inch RCP, 11 acres
off-site), and Food Lion (30 inch RCP, 7 acres off-site).
There has been some questions raised whether or not this water drained through Ms. Austin's
property or to the west of Ms. Austin's property initially. However, based on the
aforementioned 1956/1959 USGS maps, to me it appears that this property did indeed drain
through Ms. Austin's property prior to the construction of Moore Road and Food Lion. Because
this property always drained through Ms. Austin's property, and because typically development
requires that developers construct systems to handle off-site drainage in a developed condition,
my recommendation would be that the City strongly consider option number I which looks at
just the change in the actual drainage basin area to consider the participation in the solution to
the drainage problem.
I would be happy to discuss this opinion with you at your convenience.
austin.adr