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Woodridge-CS 941209December 9, 1994 Gary Daniels, President Woodridge Homeowners' Association 911 Rolling Brook Coppell, Texas 75019 RE: Woodridge Drainage Channel Dear Mr. Daniels: This letter is written as a follow-up to our telephone conversation of December 8th, 1994 in which we discussed various options available to the Woodridge Homeowners' Association to insure the construction of the Woodridge channel from Sandy Lake to Maple Leaf. As stated, there are basically three options available to the Woodridge Homeowners' Association. I recommended the best option would be to attempt to include it as part of the Sandy Lake Road project. I stated that once Council authorized staff to proceed with the project, then I would ask our consultant to look at the scope of services to determine what it would take to include the remainder of this channel as part of the Sandy Lake Road project. Once I had that change of scope, I would present it to City Council so the scope of services for the design of Sandy Lake Road could be revised and the construction of the channel could be included with the Sandy Lake Road project. The second option we discussed was to let the project run its course and be constructed when its number came up as part of the City-Wide Storm Water Management Study. This project is listed as part of the Phase IV implementation. There are currently twenty-five projects between where we are today and the Woodridge Channel project. The total cost to implement those twenty-five projects is approximately 2.7 million dollars. As you can see, if we stay with the outline in the Storm Water Management Study, the City would need to have the funding to construct the twenty-five projects before we could even address the Woodridge channel. The third option that we discussed was to try to petition Council to redirect funding internally to allow for the construction of the Woodridge channel. Per our Storm Water Master Plan, the estimated cost for this channel is approximately $500,000. That number could probably be reduced based on the improvements currently included in the Sandy Lake Road project. The timetable for the start of construction for Sandy Lake Road is eighteen to twenty-four months after Council authorizes staff to proceed. This lengthy timetable is based on the fact that we still need to finalize preliminary and final construction plans, coordinate the lowering of the 30" City of Dallas water line, coordinate the lowering of a Lone Star Gas line and purchase all of the necessary right-of-way. Based on that timetable to begin construction, it is easy to see that the actual time to complete construction would be approximately three and one-half to four years after Council authorizes staff to proceed. With this letter I am including information from our City-Wide Storm Water Management Study which covers the various phases and the written information concerning the Woodridge channel. For your information the Woodridge channel is shown as Site '0' on the Phase IV implementation. I hope this information has been helpful to you and the Homeowners' Association. I look forward to discussing this issue with you in the future when the Sandy Lake Road project proceeds. Sincerely, Kenneth M. Griffin, P.E. Asst. City Manager/Dir. of Public Works cc: Jim Witt, City Manager file/kgriff'm/wodrdge.ltr N. Mac. Arthur Boulevard/Sandy Lake Road 1. Statement of Problem Storm runoff from Sandy Lake Road spills through the intersection of Sandy Lake Road and MacArthur Boulevard. 2. Summary of Data A field reconnaissance of the area was made on June 26, 1990. City topographic maps were also reviewed. 3. Analysis of Existing Conditions A 'Y' inlet is located at the northwest owner of the intersection. This inlet and the ditch draining to it are set at too high an elevation for runoff to enter the storm sewer system without flooding the intersection. 4. Proposed Solution The ultimate improvement of Sandy Lake Road will solve this problem. In the meantime, the 'Y' inlet should be removed and replaced with a storm sewer headwall. The existing ditch could then be graded for more capacity. This solution is estimated to cost $12,000. O. Woodridge Channel 1. Statement of Problem The Woodridge channel, (Figure VII-14) south of Sandy Lake Road from MacArthur Boulevard to Mapleleaf Lane is an earthen channel which requires extensive manpower and specialized equipment to maintain. The channel bottom and side slopes are eroding causing areas to hold water creating stagnant pools which provide habitat for mosquitos, snakes and rodents. 2. Summary of Data Review of drainage for the Woodridge channel did not reveal any flooding complaints. The major concern is erosion, slope failures, and the stagnant pools of standing water. Field reconnaissance immediately after severe storms in the Spring of 1990 also indicated no flooding problems. The sandy loam soil of this charmel has a high erosion potential and two areas of slope failure were noted. Construction plans for this subdivision were requested from the City of Coppell and Lichliter Jameson and Associates, the engineer for the Woodridge developments. This subdivision is approximately 10 years old and only a portion of the storm sewer plans could be located. Channel improvement plans and MacArthur Boulevard plans were unavailable. In light of this, field survey work was performed to determine channel conditions at critical locations, such as MacArthur Boulevard and the first drop structure upstream of MacArthur Boulevard. VI1-34 3. Analysis of Existing Conditions In order to analyze the existing channel conditions, a hydraulic computer model was developed utilizing the Corps of Engineers (COE) HEC-2 program. Discharges were developed using the traditional storm sewer design methods and zoning information from the City of Coppell Comprehensive Plan. Figure VII-14 shows the 100-year flood plain. This flood plain delineation also indicate no flooding problems along this channel. Velocities in the earthen channel portion of the reach from MacArthur Boulevard to Mapleleaf Lane are 5 to 7 feet per second (fps). Velocities at the drop structures are as high as 14 fps. In the earthen portions of the channel the 2-year flood velocities are even higher than the 100-year. These velocities range from 6 to 7 feet per second. The City ~l' Coppell criteria specifies that the maximum design velocity for unlined earth channels in vegetated sandy soils is 6 fps. 4. Proposed Solution a. Alternatives Considered Concrete Channel Lining A concrete-lined channel was considered which would extend from MacArthur Boulevard to Mapleleaf Lane utilizing the existing concrete drop structures. The channel would have a 10 foot bottom width and 2.5:1 side slopes with a total topwidth of approximately 45 feet. The channel lining would extend 1 foot above the 2-year flood elevations. The adjoining areas would have less than a 4:1 slope and would be grassed to the bordering alleys. This channel would look similar to the existing concrete channel upstream of Mapleleaf Lane. The estimated probable cost of this alternative is $530,000. ii. Concrete Pilot Channel A concrete pilot channel with earthen side slopes beginning 2 feet above the channel bottom was also investigated. This would preserve the aesthetics of the channel and reduce downstream siltation by protecting the channel bottom from erosion. The pilot channel would have a 10 foot bottom width and would extend up the side slopes for 2 feet at a 2:1 slope. The earthen side slopes would then be graded with 4:1 slopes to the adjoining alley elevation. Erosion control material would be placed along the edge of the concrete and thc slopes would be grassed. The estimated probable cost of this alternative is $337,000. b. Recommended Solution The concrete channel fining (Alt. i.) is the recommended solution as it will most effectively eliminate erosion problems, as well as problems stemming from standing water. The concrete pilot channel, though less effective in protecting against erosion and requiring more extensive maintenance, would be a lower cost alternative solution. An interim solution would involve the installation of erosion control in the form of grouted riprap at the bank erosion occurring near station 30+00 and downstream of the drop structure near 34+00. The estimated cost of this interim solution is $9,000. These solutions are shown on Figure VII-14. VII-35 .~1-- U.lZ ZuJ ~.. o< o_z ~:< z by the city council of the City of Coppell. Several of the flood control projects proposed in this report could also be funded through joint efforts with individual property owners, developers or other entities. These projects are indicated in the phasing plan and each phase contains a general discussion of recommendations for the implementation of that phase. In general the implementation plan is divided into six phases. Phases 1 and 2 correlate approximately to the existing $800,000 approved by the citizens of Coppell for drainage improvements. Additional funding will be required to complete the subsequent phases of the proposed improvements. Each flood control project is self-sustaining, in case further improvements are rejected in future bond programs. Other possible funding sources are discussed in Section C. All cost estimates shown are in 1990 dollars and include engineering, construction, surveying, testing and easement or right-of-way documentation. Acquisition costs of real estate as easements or rights-of-way are not included. B. Phasing of improvemcnts 1. Phase 1 Implementation Phase t consists of projects which have already received tentative approval for funding by the Coppell City Council. Also included in this phase are additional high priority projects which could be funded, at least in part, out of the first sale of bonds. Policies, which can be adopted immediately, are also recommended as part of the Phase I Implementation. These projects may be scheduled for the 1990-1991 fiscal year. Previously Approved Projects: Site D Kaye Street (North) v$ 102,000~ Site C Brooks Lane - Stage I o$ 162,000 Site J Sandy Knoll/Shadowcrest - Stage I 4; 22,000 Site J Sandy Knoll/Woodhurst Pavement x.$ 19,0002 Site M Meadows Subdivision - Stage I ~'~ 45,000 Subtotal $350,000 Additional Projects: --------,,~--~' Site M Grapevine Creek Site B ~ Site L Table VI-4 Site O Section VI.D.50. Meadows Subdivision - Stage II Engineering Erosion Control - Survey, Engineering & Geotechnical through preliminary construction plans Bullock and Howell Subdivision Ditch Improvements Samuel Blvd./Meadowridge Condominium Flooding -Passive Warning Systems with Signs and Guardrails Woodridge Channel Interim Erosion Re~aLrs~ Staff Gage & Rainfall Gages TOTAL PHASE 1 20,0OO 4s,000 37,0003 x$/69,0003 $ 26,000 $ 9,0004 $ 4,000 $ 560,000 The developer of the adjoining subdivision has apparently committed approximately $40,000 to this project Subgrade Failure Repair Possible Cost Sharing with Coppell Independent School District Possible installation by city forces VIII-2 Other Phase 1 Recommendations. Grapevine Creek - Erosion near LBJ Freeway - City staff should initiate a coordination meeting with the adjacent developers/property owners to encourage a cooperative construction program for the proposed drop structure. Elm Fork and Denton Creek - Send request to Fort Worth District Corps of Engineers regarding detailed study of the Elm Fork and Denton Creek in the Feasibihty Phase of the Upper Trinity River Basin Study. Adopt the valley storage preservation and other recommended ordinance revisions by amendment to the existing Flood Plain Ordinance. Adopt a construction site erosion control ordinance. Initiate a roadway ditch improvement program with city forces. Initiate a street maintenance program for repair of subgrade failures. Initiate a creek inspection program. - Enforce finished floor certification by a Registered Public Surveyor for all new construction adjacent to the flood plain. Probably the most important flood control recommendation in the Coppell City-WMe Storm Water Management Plan is also included under Phase 1 Implementation. This recommendation is that the existing valley storage characteristics of the channels and flood plains within Coppell should be preserved. Valley storage is the term used to describe a stream's natural capacity to store some portion of the runoff volume as a flood wave moves downstream. Previous studies have shown that flood plain encroachment and/or channel modifications typically reduce the valley storage of the stream, generally increasing downstream flooding. It is also recommended that all designs along the creeks of Coppell be based upon 100-year flood elevations for a fully developed watershed. The minimum finished floor for all new construction should be 2 feet above this 100-year flood elevation. The adoption by ordinance of this criteria as well as the other recommendations listed above are very in~portant parts of the Phase 1 Implementation Plan. The Phase 1 Implementation plan totals approximately $560,000. Several of these projects could be funded in part by other entities as indicated in the table. It is recommended that design for all of these improvements be initiated immediately. It should also be noted that the Meadows-Stage II diversion design and easement documentation is recommended during the Phase I implementation. This diversion is required to reduce street flooding on Parkway Boulevard. There is already evidence along Parkway Boulevard of storm runoff flowing over the top of curb and this condition will worsen as the area continues to develop. The diversion is proposed through Waterside Estates to an existing lake. Thus far, the lots within this subdivision have not been developed. An easement for the outfall should be obtained before the lots are sold and homes are constructed. VIII-3 Phase 2 Implementation Phase 2 consists of projects which may be funded, at least in part by the second sale of bonds for the fiscal year 1991-1992. Stream G6 (~LWE) "~'. Stream G 1 }cvine Creek )evine Creek $ 170,000 S 31,000 S 7 Bethel School Road; Channel; and Culverts Lx)ch Lane Channel Improvements Erosion-Unnamed Grapevinc Creek Trib at Meadowcrcek Dr. Erosion-Unnamed Grapevine Creek Trib Downstream of Meadowcreek Dr. Andrew Brown Park Spillway Kaye Street (South) Cozby Circle Moore Road - Austin Property and Town Creek Apartment Flooding Swan Drive Fieldcrest Loop $ 83,000 Denton Creek S 35,000x Site D S 111,0002 Site D S 17'0002 Site L $ 28'0002 S 30,000 Site I Section S.2 $ 61'250x3 TOTAL PHASE 2 $ 573,250 Parks and Recreation Department Possible cost sharing with property owners Estimated cost from "Preliminary Engineering Study for Drainage Problems on Fieldcrest Loop" by Ginn, Inc. July 14, 1989. Phases 1 and 2 represent over one million dollars in improvements to the drainage systems within the City of Coppell. The majority of these projects may be funded with the previously approved drainage improvement funds included in the 1990 bond package. However, sources of additional funding should be pursued by city staff. Projects such as Fieldcrest Loop, Kaye Street (south) and Cozby Circle should be funded at least in part by the property owners with city staff taking the lead in coordination and construction supervision. For example, the Cozby Circle drainage improvements on the individual lots could be funded either by the home owner or by the developer of the Cooper Road lots while the City funds the design and construction of the connection into thc existing storm sewer inlet on Anderson Avenue. Other projects, such as, the Sandy Knoll/Woodhurst subgrade failure and the Andrew Brown Park Spillway should be funded under street repair and Parks and Recreation funds, respectively. VIII-4 private funding. Phase 3 Implementation Phase 3 consists of projects which have a high priority but may require additional public or Grapevine Creek Stream G3 Stream G4 Site P Stream G6 (NLWE) Stream G5 Stream G2 Site F Stream G1 Cottonwood Branch Site E Erosion - Denton Tap Road to Moore Road Meadowcreek Road Improvements S 29,000 Meadowcreek Road lmprovemenLs S 53,000 Mapleleaf Lane - Stage I S 49,0~X) Moore Rd. Erosion Protection S 230,000 $1,350,000~ Erosion Protection & Grading $ 7,000 (Carter Rd. & Christi Ln.) Erosion Protection behind S 26,000~ Plantation Dr. residences Cottonwood Estates/Summer S 42,000 Place Addition Freeport Parkway/Bethel Road S 69,000~ Intersection (Coppell Commerce Center) Andrew Brown Park Berm S 35,0002 Golden Triangle Mobile Home Park $ 90,000~ TOTAL PHASE 3 $1,980,000 Possible cost sharing with property owners, developers and builders. Parks and recreation funding. VIII-5 4. Phase 4 Implementation Phase 4 consists of projects where some improvements have already been accomplished in previous phases or by the property owner. Also included are projects which received a very low priority rating and are not recommended for improvement at this time. These areas should be monitored and additional improvements funded on an as needed basis. Site P Mapleleaf Lane - Stage 1I $ 28,(X)0 Site M Meadows Subdivision - Stage II Construction $ 130,0(X) Stream G1 Erosion Downstream of Coppell $ 22,000~ Road (Mitchell Street) Site C Brooks Lane - Stage II $ 63,000 Site J Site O Site K Sandy Knoll/Shadowcrest - Stage II $ 60,000 Woodridge Channel - Concrete Lining $ 530,000 Parkwood Channel $ 405,0002 (concrete side slopes) Stream G6 (NLWE) Marshy areas along channel Stream G6 (NLWE) Tributary immediately north of Bethel School Road - Overlot drainage causing erosion 15,0004 Site I Hawk Lane $ 26,000 TOTAL PItASE 4 $1,279,000 This property owner is currently in the process of correcting the most severe problem in this area. Per city staff, maintenance on this channel is approximately $4000 per year. Field inspection did not show any severe, erosion problems at this time. French drain system installed by the property owner estimated to cost $2500 per lot. Existing railroad tie retaining wall should be monitored for failure. VIII-6 II II 5. Phase 5 Implementation Phase 5 consists of projects which will probably be funded during the course of adjacent land development or as part of the thoroughfare program. Stream G1 Stream G1 Grapevine Creek Site A Site H Site G Site L Grapevine Creek Stream G1 Stream C1 Stream D1 Coppell Road $ 488,000 Bethel School Road $ 555,000 Erosion near LBJ Freeway $ 400,000 Freeport Parkway near Southwestern $ 280,0'00~ Boulevard (Undersized storm sewer) -_ Shady Dale Lane (culvert only) $ 39,000 Whispering Hills/Sandy Lake Rd. $ 56,000 Moore Rd. Drainage Improvements $ 249,000 Belt Line Road Improvements $ 560,000 Bethel Road $ 426,000 State Road (Freeport Parkway) $ 60,000 Coppell Road Culverts $ 118,000 $ 750,000 $ 12,000 $3,993,000 Cottonwood Branch State Road - Freeport Parkway Site N MacArthur/Sandy Lake Road TOTAL PHASE 1 Re~mmendation not made; less expensive alternative shown for comparison. 6. Phase 6 Implementation Phase 6 recommendations generally preserve or enhance the existing channels and flood plains of the City of Coppell but may not reduce the flooding of any existing structures. Also included are recommendations which benefit the city overall although not directly flood plain or flood control related. Parallel Parkway System $2,700,000~ Greenbelt Preservation/Open Space Acquisition 286 acres Hike and Bike Trail Additions City-Wide Survey Monumentation System $ 880,0002 TOTAL PHASE 6 $3,580,000 Estimated cost is total project cost. Developer participation is probable but is not estimated. Estimate for ten foot wide concrete trails. Information provided to city staff separately. VIII-7