Gateway BP(1.1)-CS 911029MEMO
TO: Gary L. Sieb, Director of Planning and Community Services
FROM: VM. Shohre Daneshmand, Acting City Engineer
SUBJECT: Gateway Business Park
Infrastructure Development
(Letter from Catellus, dated 10- 15 -91)
DATE: October 29, 1991
FILE Corr
The subject "downstream drainage" improvement, as cited in the referenced
7 letter from Mr. Davis to Mr. Ratliff, has been identified in the City's
Storm Water Management Report. (Please see attached)
I provide the following comments, within the limited time provided to me
and based on my quick research and findings:
If Catellus developed the 78 Acre tract, the amount of
ultimate storm runoff would not be handled by the existing
storm system under Freeport Parkway.
Basically, the drainage outfall from Catellus' property is
proposed to be discharged to Grapevine Creek by means of a
storm system passing through Prentiss Property (known as Park
West Commerce Center). (See attached map)
In the past, Staff had encouraged the two developers, Catellus
and Prentiss, to resolve this problem, which appears to affect
both developers. To this date, we have not been informed of
any type of resolution.
The preliminary construction plans for Southwestern Blvd.,
prepared for Prentiss, shows the proposed 8' X 6' box culvert,
as recommended. It is not clear whether Prentiss will
construct this culvert.
This drainage improvement is included under Phase 5 of the
suggested implementation plan in the City's Storm Water
Management Report. The estimated probable cost for this
improvement is $280,000. There are no City funds available for
this improvement at this time.
It is recommended that this matter be resolved between affected
developers, Catellus and Prentiss. Any active participation by the City,
in resolving this drainage concern, would require the City Council's
consideration of approval and reprioritization of drainage improvement
projects.
Memo to Gary L. Sieb
October 29, 1991
Page 2
Please note that it is unclear to me whether Mr. Davis' request for "Fast
Tracking of platting process" relates to the above referenced
drainage improvement or not.
Please let me know if you need additional follow -up.
MSD /bd
GATEMEM
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VII. LOCAL DRAINAGE PROBLEMS
ALTERNATIVES AND RECOMMENDATIONS
In 1989, a subcommittee was formed to address drainage problems within the City. The Natural
Drainage Subcommittee was one of eight subcommittees made up of volunteer citizens working together with
city staff to identify public improvement needs within the City of Coppell. This committee toured sites where
specific drainage complaints had been received. Table I -2 is a list of these specific sites as compiled by that
committee. The sites are shown on Figure I -1. Recommendations in this Chapter will address these problem
areas and other drainage complaints compiled from City files that are not directly related to problems along
stream channels discussed in the previous chapter. The City of Coppell continued to receive citizen complaints
throughout the course of this study. A compilation of all these drainage complaints is included in Appendix
C of this report. The majority of these problem areas stem from undersized storm sewer systems including,
in some cases, lack of roadway ditch drainage capacity. Erosion sites on two streams not in the original scope
of work, Parkwood Channel and Woodridge Channel, are also addressed in this chapter. The drainage
problems are grouped into sixteen sites by area, as shown in Table VII -1. In addition, many of the similar
complaints and miscellaneous problem areas are grouped together and presented at the end of the chapter.
For example, some of the street flooding and standing water complaints are due to pavement subgrade failures
and differential pavement settlement. In other areas, the problems stem from roadside ditches and drainage
wales which are weed and/or silt choked. These types of problems are shown on Table VII -1 as Street
Maintenance and Roadway Ditch Maintenance, respectively, and discussed at the end of the chapter.
Miscellaneous problem areas which should be corrected by the individual property owners and other
neighborhood drainage studies are also included. Twelve of the Local Drainage Sites have been addressed
previously in a May 15, 1990 council workshop and preliminary report. (1) Information on those sites is also
included in this chapter.
The following chapters discuss problems and proposed solutions for the problem sites. Improvements
proposed in this study are designed to current City of Coppell Drainage Standards. Those standards specify
the use of the City of Dallas' Drainage Design Manual.m The manual recommends that all drainage systems
(inlets and pipes combined with street and emergency overflow capacities) be designed for the 100 -year flood
discharge. Analyses of existing storm sewer systems were performed utilizing "as built' construction plans
obtained from city files where available. Estimates of probable cost were calculated using City of Dallas Public
Works Department currently stored unit prices as of April 2,1990, where applicable. The total estimated costs
include construction, engineering design, geotechnical testing, surveying, and easement documentation.
Easement acquisition cost is not estimated.
Freeport Parkway near Southwestern Boulevard
1. Statement of Problem
Storm runoff from a large (78 acre) undeveloped area bounded by the St. Louis and
Southwestern Railroad on the north, Freeport Parkway on the east, proposed Gateway Boulevard on the
south, and Cotton Road on the west, flows along the railroad through an abandoned city water storage facility
and over the curb into a storm drain inlet on Freeport Parkway (Figure VII-1).
Most of this property, Gateway Business Park, is owned by Catellus Development Corpora a
(formerly Santa Fe Pacific Realty Corporation). In a letter dated September 26, 1990, Catellus exp E
concern about inadequate storm sewer capacity in Freeport Parkway.
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VII-1
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2. Summary of Data
Existing conditions are reflected on the 1985 city topographic maps. Drainage plans dated
1981 for Freeport Parkway were obtained. Proposed plans for Gateway Business Park were also reviewed.
In addition, field reconnaissance of the problem area was made in April 1990, immediately following a storm
event.
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3. Analysis of Existing Condition
Storm water runoff from this large relatively flat area flows generally north and east towards
the railroad right -of -way. There are no defined drainage channels. Prior to entering the right -of -way, runoff
is diverted by a berm which causes the flow to travel east along the right -of -way. Al one point, approximately
1000 feet west of Freeport Parkway, the berm is broken and drainage from the railroad actually enters the
adjoining property, thus aggravating the problem. At Freeport Parkway the flows concentrate, flow through
the abandoned water storage facility site, and over the curb into the drainage system. The curb inlet is not
sized to handle the runoff from this large area even in its undeveloped state. Because of the large drainage
area and flat slope of the undeveloped tract, the excess storm water flow will persist long after rainfall has
ended. This problem is temporary and should be solved with the development of the Catellus site.
The inadequate storm sewer in Freeport Parkway is a more serious problem. The existing
system picks up drainage from this 78 acre site at the southwest corner of the intersection of Freeport Parkway
and the St. Louis and Southwestern Railroad (SL SW RR). Storm water travels via a 60 -inch reinforced
concrete pipe (RCP) south on Freeport Parkway to Southwestern Drive. Before entering Southwestern Drive
and flowing east, the storm sewer pipe increases to a 66 -inch RCP. Several curb inlets in Freeport Parkway
are connected to the 66 -inch RCP. About 1000 feet east of Freeport Parkway, the 66 -inch storm sewer outfalls
to an open channel which conveys storm water to Grapevine Creek.
At Freeport Parkway, the 1981 drainage plans show a capacity of 174 cfs for the storm sewer
system. Drainage calculatio usin current City of Coppell standards indi a r 'aired capacity of about
530 ei. This shows that the existing system is grossly un s erstzed, most_p_mbalik because it was ign
existing undeveloped land uses and a lower (5 -year versus 100 year) design criteria than is currently used in
the City of Coppelt In addition, the existing headwall is set at a high elevation to avoid outer utility lines and
the system will only flow half full before street flooding of Freeport Parkway occurs.
Ikt Development of the adjoining 78 acre site will require some extraordinary drainage
improvements because of the inadequate storm sew re m Freeport Parkway.
4. Proposed Solutions
a. Interim
The St. Louis and Southwestern Railroad should be requested by letter to repair the
berm and maintain the drainage ditches along the railroad. A 2- to 4-foot high berm should be constructed
along Freeport Parkway and the flows redirected to the existing storm sewer headwall (Figure VII -1). These
modifications should be performed by the railroad and the property owner.
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b. Permanent
c. Recommendations
The two most likely improvements to permanently solve this drainage problem are
detention and additional storm sewer construct ion. Detention as an alternative would reduce runoff peak
flows to equal the capacity of the existing system. Storm sewer improvements would consist of constructing
additional capacity to supplement the existing system.
One or more detention basins could be constructed on the Catellus site to reduce
peak runoff rates. The detention basins could be linear and actually replace some of the interior drainage
facilities within the site. The basins would reduce the 100 -year peak runoff rate from 530 cis to less than 200
ds which could then be handled by the existing system. A new 66 -inch RCP outfall would be constructed to
convey floodwaters to the existing 60 -inch RCP in Freeport Parkway. The detention alternative is estimated
to cost $400,000 for basin excavation and outfall facilities. This alternative will require approximately 4 to 6
acres of land of which 0.25 acres is owned by the City. Without detention, the estimated cost of the onsite
storm sewer facilities that Catellus would otherwise have to construct is S730,000. Easements for those
facilities would require about 1.3 acres of land making the net land requirement for the detention alternative
approximately 2.4 to 4.4 acres depending on final basin configuration and related storm drainage
improvements. This alternative is shown schematically on Figure VII -1.
Underground storm sewer improvements could be made in Freeport Parkway and
Southwestern Drive to provide an outfall for the fully developed 100 -year discharge of 530 cis. An 8 x 6 foot
box culvert would be required at an estimated cost of $280,000. This plus the previously mentioned onsite
storm sewer costs of $730,000 bring the total estimated project cost to S1,020,000 for the underground storm
sewer alternative.
An unlimited number of combinations of detention and downstream storm sewer
improvements are possible. A smaller detention basin with some downstream storm sewer improvements
would cost more than the detention alternative and require more drainage right -of -way. Regardless of the
ternative selected, final dimensions, grades, and facility size should be determined by the developers'
engineers. Information provided here is for guidance only and answers feasibility questions concerning each
alternative.
The interim solution (berm construction and ditch maintenance) is recommended and
could possibly be implemented with construction of Gateway Business Park.
VII-4
The detention alternative will have minor downstream flood plain management
benefits. The reduced discharges will result in outfall flows to Grapevine Creek being approximately equal
to existing, undeveloped conditions. This alternative also should have some minor water quality enhancement
benefits. The detention alternative is more expensive than the offsite storm sewer improvements, especially
if the cost of land is included. However, when combined with the cost of onsite improvements, the total cost
of the two systems (land, onsite and offsite storm sewer improvements) is similar.
ge The advantages of the un and storm sewer im rovements include less land foe
re�uirements. The 4 to 6 acre requirement of the detention basin alternative is roughly equal to an additio
i From the v iewpoint of th city, i uer to cons the offsite storm sewer
improvements than to fund the detention alternative construction.
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XI
STORM
M1NVARDS
EXISTING PATH
OF CONCENTRATED
E
LOW -fNT-EF_..._..._".
CONSTRUCT EARTH
EXISTING
i STORM
EWER
ACITY= 200cfs.
It P J
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1 u
DETENTION ALTERNATIVE
AREA 4 -6 ACRES---
OUT =200cfs.
CATELLUS DEVELOPMENT,
UNDER GRQUND STORM WER ALT.
INSTALL 508 L.F. 8'x6' BOX VERT
ALONG SOUTHWESTERN BLVD. OUTFALL
TO GRAPEVINE ,CREEK ALONG PROPOSED
RAILROAD SP EE PLATE 3-6)
CAPACITY=
FUTURE GAS BUSINESS PARK
0
100
REDIRECT RU
TO EXISTING
HEADWALL
200
300
SCALE IN FEET
PRENTISS PROPERTIEi
FIGURE VII -1
SITE A
FREEPORT PKWY. NEAR
SOUTHWESTERN BLVD.
ON
1,