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HomeMy WebLinkAboutCENTRE FOR ADVANCED TECHNOLOGY TECHNOLOGY - FEBRUARY 2003 - Filed O-ODP/MASTER PLANS -NORTHERN ENGINEERING NESERVICES, INC. June 13, 2002 Revised November 27, 2002 Basil Hamden City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, CO 80521 Re: Master Drainage Summary for the South Campus Overall Development Plan For the Colorado State University Research Foundation Dear Mr. Hamden: The purpose of this letter and exhibits is to summarize the approach taken in master planning the drainage facilities for the remaining parcels of the South Campus Overall Development Plan (ODP) based on the City of Fort Collins review comments. This letter report is meant to review previous drainage analyses in the area, analyze the potential impact of the new rainfall intensity curves adopted by the City of Fort Collins, and provide a conceptual design of how stormwater is to be detained, treated and conveyed through the proposed development parcels. It is understood that no extensive SWMM modeling effort is required for this level of development, therefore, the individual parcels have been evaluated using the rational method with outfall rates limited to the rates specified by previous drainage studies. It should be pointed out that the basin areas used in this analysis are approximate and are based on the developable area. Areas are not the same as the parcel areas, which are gross acreages. For ease of reference the parcel areas and basins are given similar references, i.e. Parcel A corresponds to Basin A or Basin C 1, C2 and C3 are in Parcel C. Previous Drainage Studies Parcels A & B Parcels A and B are proposed to have office/commercial uses. These parcels were originally analyzed in the report Master Drainage Report for the Centre for Advanced Technology. Special Improvement District by RBD Engineering Consultants dated February 1987 (Original Master Drainage Plan). This master plan used the rational method of analysis. In this report Parcel A represented Basins G1 and G2 and Parcel B represented Basin F. In accordance with this original report each of these parcels was required to detain 100-year developed flows and outfall them at the 2-year historic rate. In this original report no provisions were made for water quality treatment, since those requirements were not in place at the time the report was written. In addition, both these sites were to ultimately outfall into the piped storm drainage system in Centre Avenue. More recently the drainage for Parcel A was analyzed as part of the CSU South Campus Veterinary Teaching Hospital Drainage Evaluation (South Campus Drainage Evaluation), which was prepared by Anderson Consulting Engineers for the CSU Facilities Management (dated October 19, 2001). This study combines the drainage from Parcel A with the adjacent CSU 420 SOUTH HOWES, SUITE 202 / FORT COLLINS, COLORADO 80521 / 970.221.4158 / FAX 970.221.4159 parcel to the east. This CSU parcel has changed in its configuration in recent years with the relocation of the Larimer County Canal No. 2 and the master planning that has been done for the Veterinary Teaching Hospital. The drainage approach taken in this summary proposes no change to the approach taken in the South Campus Drainage Evaluation. The drainage for Parcel B will be analyzed for the area covered in the original Master Drainage Plan (February 1987) minus a small area at the extreme northeast corner of the original parcel, which was cut off from the parcel when the Larimer County Canal No. 2 was relocated for the construction of Centre Avenue. Parcel C Parcel C is proposed to have office/commercial uses and may include student housing. A portion of this parcel was originally analyzed in the Original Master Drainage Plan. This portion consisted of the eastern end of Basin E in this report. This Basin has since been split into two ownership groups, therefore, the original basin is not relevant to the new development considerations. Parcel C was also discussed in the report Addendum No. 2, Outfall Swale Design for the Windtrail P.U.D., by Lidstone & Anderson dated August 7, 1995 (Outfall Swale Report). This report was done to establish the design approach taken for the ultimate design of the outfall swale that conveys the drainage for the Wind trail Park P.U.D. development, southern portions of the Windtrail P.U.D., the Sundering Townhomes, and what are now Basin C1 and C2 and the adjacent portions of the proposed extension of Rolland Moore Drive (see Master Drainage Exhibit). These areas consisted of Basin A through L in the Outfall Swale Report. These areas were allowed to outfall directly into the outfall swale with no detention requirement. The Outfall Swale Report also clarified that Basin G and M of the report were to outfall directly into the Arthur Ditch. It should be noted that this is more correctly identified as the Sherwood Ditch and that the City no longer allows discharge directly into the Sherwood Ditch. Basin G in the Outfall Swale Report reasonably approximates all of Basin C3 and the adjacent portion of the proposed extension of Rolland Moore Drive in this report. Basin M in the Outfall Swale Report comprises a narrow f50-foot wide corridor along the western edge of the City of Fort Collins Horticultural Center site. In a similar approach, these areas were allowed to outfall without detention requirements. Parcels D, E & F Parcel D is proposed office/ recreation/commercial/parking, as is Parcel El. Parcel E2 is proposed recreational/parking and Parcel F is proposed office/commercial. These parcels have not yet been analyzed by previous drainage reports other than the Spring Creek Basin Master Plan dated November 20, 2001. This report has shown that Parcels D and E are inundated in the 100-year event and lie within the 100-year floodway. This means that no structures could be built on these parcels in their present conditions. This would restrict development to recreation uses. CSURF recognizes these restrictions but reserves the right to develop these sites if they can be taken out of the current floodplain. [:}:'f'reii t4.L}C)!'`Chain.*`•iZ<��<�ev4'.?tat;rk:}�;tii::xgcil-.'-t;2.c{:�c 2 Parcel F remained developable based on the Spring Creek Basin Master Plan and FEMA mapping. New Drainage Criteria Since the Original Master Drainage Plan and the subsequent Addendum, drainage criteria for development within the City of Fort Collins has changed. In 2001 the City of Fort Collins adopted revised rainfall intensity curves based on the problems incurred during the flood of 1997. The reports before this date, including the Original Master Drainage Plan and its Addendum, used the original rainfall intensity curves. This report therefore will recalculate the required detention volumes based off the new intensity curves. In addition, the issue of water quality detention will be addressed. The Spring Creek Floodway and Floodplain boundaries as defined by the City of Fort Collins have recently changed as a result of new modeling contracted by the City. The new boundaries shown on the attached Master Drainage Plan are the result of the Spring Creek Basin Master Drainage Plan — Baseline Hydraulics prepared by Anderson Consulting Engineers, Inc. dated February 15, 2002 hereafter referred to as the New Spring Creek Master Plan. Conceptual Design of Drainage Facilities Parcels A & B The increased rainfall intensities directly affect the drainage flows and detention volumes. Basin areas for these parcels have been modified to reflect the updated boundaries, as discussed above, but the runoff coefficients have remained the same. Times of concentrations were calculated from the conceptual layout plan. The drainage pattern for Parcel A (Basin A) has been changed to reflect the parcel's natural slope to the east and to conform to the drainage approach taken with the South Campus Drainage Evaluation. As stated earlier, the South Campus Drainage Evaluation combined the drainage from Parcel A with the adjacent CSU parcel to the east (Basin 89 in the South Campus Drainage Evaluation). It is highly probable that these two parcels will be combined in the future to form a much more developable parcel. The current South Campus Master Plan, in fact, reflects this scenario. The following Table A reflects this approach for the Ultimate Basin A configuration. The outfall for the Ultimate Basin A pond will be piped under the Larimer County Canal No. 2 and into an open channel or pipe running east just south of the south property line of the NRRC site. This drainage conveyance will ultimately outfall into the open channel constructed with the CSU Veterinary Pond Outfall. The alignment of the outfall conveyance has been incorporated into the CSU's current planning of the South Campus Master Plan according to John Morris of CSU Facilities Management. The attached drainage exhibit reflects the parameters for the Ultimate Basin A Pond and outfall and Basin A's proportional contributing area. The drainage patterns for Parcel B (Basin B) remained unchanged and the revised figures illustrate the impact of the new intensity curves. Summarized below are the updated values. Required detention volumes were determined using the FAA method while maintaining the outfall rates determined in the Original Master Drainage Plan. It should be pointed out that no drainage flows (up to and including the 100-year event) are intended to outfall into the Larimer County Canal No. 2 from the development of Parcels A or B. Parcel A's outfall will be piped under the Larimer County Canal No. 2 and eastward into the Veterinary Hospital's outfall system. Parcel B's outfall will empty into the storm drain system in Centre Avenue. Table A Basin Area C100 Tc Allowable Storage (developed) Outfall Volume Rate cfs ac-ft Ultimate 17.1 * 1.00 21.77 3.0* 3.7* A B 16.00 1.00 14.79 2.68 ** 3.79 * From the South Campus Drainage Evaluation ** From the Original Master Drainage Plan Water quality ponds are also required on these parcels. The method described in "Urban Storm Drainage Criteria Manual- Volume 3- Best Management Practices" [September 1999] is the method used to determine volumes for these ponds. Since the exact type of best management practice (BMP) that is going to be used for these ponds is not known, the volume is estimated. This method gives the water quality capture volume as a function of the tributary catchments total imperviousness as a ratio to the total area of the catchments drain time. In this report, we assume a 24-hour drain time. Required Storage= [WQCV/12](A) Where WQCV= water quality capture volume from figure SQ-2 A= area (ac) Basin Iwq I WQCV (24) A (Ac) V (ac-ft) Ultimate A 85 .85 .36 17.1 .46 B 85 .85 .36 16 .43 Combining the required detention and water quality volumes, the following are the total required volumes for these ponds. Table B Basin Area V100 ac-ft Vw ac-ft Vtotal ac-ft Ultimate A 17.1 3.7 0.46 4.16 B 16 3.8 0.4 4.2 Parcel C Based of the Outfall Swale Report and the current Spring Creek Basin Master Drainage Plan the developable portions of Parcel C can be developed without onsite detention. Water quality detention would be required. Using the same method as described above for water quality, the volumes have been estimated and appear in Table C. D:`,§'t;?(cos !-2 '-a2.d,,)c 4 Table C Basin Iwq I W CV 24 A Ac V ac-ft Cl 70 .70 .25 3.56 .07 C2 70 .70 .25 11.38 .24 C3 70 .70 .25 9.38 .20 The developers of these parcels may choose to use the adjacent wetlands as a means of facilitating the water quality requirement for this parcel. Using this approach, no on -site water quality detention would be required, however, the use of the existing wetlands would have to be justified through the proper analysis. Basins C1 and C2 will be designed to outfall directly into the Windtrail Swale consistent with the design approach taken in the Outfall Swale Report. The City has raised concerns regarding the capacity of the outfall Swale in this area. These concerns have been address by Anderson Consulting in the Appendix to this Drainage Summary. Basin C3 will be designed to outfall through the storm drain and swale system recently approved with the City of Fort Collins Horticultural Center. This system is being designed to convey 100- year developed flows from Basin C3 through the Horticultural Center site, under the Sherwood Ditch and into Spring Creek. The area of Basin C3 which lies within the new floodplain boundary will likely be regraded to minimize the area impacted and mitigate the upstream and downstream effects of development. Parcels D, E & F Parcels D and E are in the Spring Creek Floodway as defined by both the current FEMA floodplain and the City's newly developed floodplain mapping. CSURF remains in negotiations with the City at this time to facilitate the possibility of developing athletic facilities and parking facilities on portions of Parcel E for the CSU and the Mason Street Corridor Plan. CSURF reserves the right to develop this parcel in the future should measures by the City or other private development change these conditions or address the constraints imposed by this designation. If these conditions are met, it is assumed this parcel will be allowed to develop without onsite detention. Water quality detention would, however, still be required. The City's newly developed floodplain mapping indicates that a sizable portion of Parcel F is now within the 100-year floodway. CSURF reserves the right to develop this parcel in the future should measures by the City or other private development change these conditions or address the constraints imposed by this designation. If these conditions are met, it is assumed this parcel will be allowed to develop without onsite detention. Water quality detention would, however, still be required. The Table D reflects the probable water quality detention volumes needed based on the intended land use. Table D Basin Iwq I WQCV 24 A Ac V ac-ft D 35 .35 .15 11.30 .14 E1 85 .85 .32 4.14 .11 E2 35 .35 .15 27.16 .34 F 85 .85 .32 3.2 .09 I):`%PrnJ(X..t 1-27-02.&),: 5 Summary In summary, the attached Master Drainage Plan reflects the conceptual drainage approach taken for the CSURF South Campus Overall Development Plan outlined above. This approach follows the intent of previous master planning done in the area. Storm water detention and water quality detention volumes have been amended to reflect the increase rainfall intensity curves and new drainage criteria. The drainage for each parcel in the Overall Development Plan is summarized below: • Parcel A will likely develop with the adjacent CSU parcel to the east according to the current CSU South Campus Master Plan. The outfall for these areas will be piped under the Larimer No. 2 Canal and into the outfall system for the Veterinary Hospital Pond. • Parcel B will continue to detain and release into the storm drain system in Centre Avenue. • The eastern half of Parcel C (south of Rolland Moore Drive) will flow undetained into the outfall swale draining the western portion of the site or the Horticultural Center drainage system. The portion of Parcel C north of Rolland Moore Drive and the western half of Parcel C (south of Rolland Moore Drive) will flow undetained into the Windtrail Swale north of the new Rolland Moore Drive alignment. • Parcels D and E are in the Spring Creek Floodway as defined by both the current FEMA floodplain and the City's newly developed floodplain mapping. CSURF remains in negotiations with the City at this time to facilitate the possibility of developing athletic facilities and parking facilities on portions of Parcel E for the CSU and the Mason Street Corridor Plan. CSURF reserves the right to develop this parcel in the fixture should measures by the City or other private development change these conditions or address the constraints imposed by this designation. • Parcel F is within the 100-year floodway as recently defined by the City's newly developed floodplain mapping. CSURF reserves the right to develop this parcel in the future should measures by the City or other private development change these conditions or address the constraints imposed by this designation. If these conditions are met, it is assumed this parcel will be allowed to develop without onsite detention. I trust this report provides the information needed for the conceptual drainage approach for this ODP submittal. If you have questions or need any clarification please do not hesitate to contact our office. Sincerely, J Stan A. Myers P.E. Senior Project Manager [:):.i'r;,ja:� ,<?[:)i"thainas�,`•fZc:}xtrt v9ast�?.rDi i2r,��t 3 i-2:'-02Av, 6 APPENDIX ` ANdERSON CONSUITINC, ENC�iNEERS, INC. Civil • Water Resources • Environmental October 15, 2002 Ms. Julie Birdsall, CFO Colorado State University Research Foundation P.O. Box 483 601 S. Howes Street, Suite 410 Fort Collins, CO 80522 RE: Windtrail Swale Preliminary Hydraulic Evaluation (ACE Project No. COCSRF03) Dear Julie: The purpose of this letter is to document our preliminary hydraulic evaluation of the Windtrail Swale with respect to its capability to convey existing and future storm runoff in the context of the currently proposed alignment of Rolland Moore Drive. The roadway alignment proposed for the future extension of Rolland Moore Drive was provided by Tait & Associates as depicted on Figure 1 (attached). It is our understanding that the two areas of concern for the City of Fort Collins Stormwater Department staff are the constricted reach in the vicinity of Cross Section 1340, and the swale crossing at Northerland Drive, both shown in the figure. In order to evaluate the possible conveyance capacity of the swale through the constricted reach and one potential culvert configuration at Northerland Drive, a HEC-RAS model was prepared for the swale based on the best available topographic mapping. Cross sections were defined using a composite topographic map compiled from several recently produced sets of topography. The proposed horizontal alignment of Rolland Moore Drive was superimposed on the base map. Since the vertical alignment of the road is not currently known, the effect of the road on the conveyance capacity along the Windtrail Swale was modeled using a vertical obstruction located 20 feet beyond (outside of) the proposed right-of-way. From a conveyance standpoint along the swale, this configuration would likely accommodate the roadway being elevated up to as much as five feet above existing ground along the proposed alignment. With regard to Northerland Drive, the road elevation at the south end of the existing street was assumed to extend horizontally across the swale. Without a proposed development associated with the area south of the Rolland Moore Drive extension, the current evaluation of the Windtrail Swale utilized discharge profiles previously defined for the design of the swale as documented in the report, "Addendum No. 2, Outfall Swale Design for the Windtrail P.U.D.," Lidstone & Anderson, August 7, 1995. For the purposes of the current study, the "adjusted discharge" and the "freeboard discharge" profiles shown in the attached table from the referenced report were used. The freeboard discharges are simply the 100-year adjusted discharges increased by one-third. The freeboard discharge profile was previously used to define the required conveyance corridor along the Windtrail Swale. At Cross Section 1340 in the P:• COCSRF0316VPICOCSRF03-LTR2.wpd October 15, 2002 772 Whalers Way, Suite 200 • Fort Collins, CO. 80525 Phone: (970) 226-0120 • Fax: (970) 226-0121 • www.acewater.com Ms. Julie Birdsall Page Two October 15, 2002 constricted reach, the 100-year adjusted discharge is 42 cfs and the freeboard discharge is 56 cfs. At Northerland Drive, the 100-year adjusted discharge is 80 cfs while the freeboard discharge is 106 cfs. The HEC-RAS analysis conducted for the current study found that the freeboard discharge could be conveyed through the swale at Cross Section 1340 with an additional 2 feet of freeboard prior to overtopping the left bank into the Windtrail development to the north. This condition is indicated on Figure 2 (attached) that shows both the adjusted and freeboard water levels at Cross Section 1340. The HEC-RAS analysis also determined that two 8'Wxl.5'H RCB's would likely fit under the Northerland Drive extension while passing the freeboard discharge with an additional six inches of freeboard prior to overtopping the left bank into the Windtrail development to the north. This configuration is indicated on Figures 3 and 4 (attached). Figure 3 depicts the assumed culvert installation at the upstream face of Northerland Drive, while Figure 4 illustrates both the adjusted and freeboard water levels at Cross Section 987 directly upstream of Northerland Drive. Clearly this is only a preliminary evaluation based on a number assumptions, necessitated by the lack of definitive design information for Rolland Moore Drive and the possible future development in the local tributary area. Any final swale and culvert design would need to be analyzed at a greater level of detail utilizing specific design information for the roadway and adjacent properties. I hope this information adequately addresses the comments by City staff concerning the possible future operation of the Windtrail Swale. If you or the City have any questions or comments regarding any of this information, please do not hesitate to contact me. Sincerely, ANDER!S?0��!ONSULJ G ENGINEERS, INC. ` Gre J. o , P.E. V r ident Attachments P: ICOCSRF031 WPI COCSRF03-LTR2. x pd October 15, 2002 r t Y� 71 xr . GILGALAD WAY a n z co^ ol r R �,: •'I,,,. � I i F �"'". 'aye ', r `J k z WINDTRA/ S�/AL�. L V �0. �'Q' � N to � r ry m+•y t.+'�. SCALE: 1 "=100' FIGURE 1. WINDTRAIL SWALE/ROLLAND MOORE DRIVE PLAN VIEW T , }r , G CREEK T hi *' Cyi rj O O N C M_ � II O C LO (0 d _ C II =� U a� s O O II O O O Irlozld �'�7.3� -1J-� o 0 O� o o 0 0 C c o a m to LO LO LO LO ()}) UOi;eA913 iv v � � C i m � � m � c (n J ? li � m i W � ! W .0 0 i O 1} 1+Vl�'J'z' �i�S?t21.Qde2:ci O O N co co O � II O CO C `p f0 C r C II t (0 U N C O y O (n l0 c0 O 7 II O NLO O O O O o 0 S c 0 LO LO LO � LO LO (4) UOIJEA919 pppy « C � O � N y C fn J a � LL LL. jQ m ! W 3 ! W Table 3.1. Design Discharge Profile (100-Year Event) for the Windtrail Outfall Swale. Design. Point: Cross Section Original Discharge (cfs) Adjusted Discharge (cfs) Freeboard Discharge" (cfs) 8 1 128 211 281 5 250 96 179 238 9 800 95 95 126 4b 1107 80 80 106 3a 1450 42 42 56 Freeboard Discharge = 1.33 x Adjusted 100-Year Discharge It is noted that CSURF originally requested that the downstream -most 400 feet of the Swale be oversized. Due to the current swale configuration, which includes a berm along the swale's southeast perimeter, directing future runoff into the swale at Station 4+00 may be problematic. Consequently, the current swale design has incorporated the requested over -sizing up to, but not including, Station 8+00 (Cross Section 800); for additional documentation, reference is made to Appendix C. A "freeboard discharge" column is also given in the table. The freeboard discharge is hereby defined as the adjusted 100-year discharge plus one-third. The freeboard discharge profile was used to define the required freeboard boundary associated with the outfall swale; that is, the boundary which defines the areal limit required to pass 1.33 times the 100-year discharge. 3.2 Hydraulic Analysis In addition to the regrading necessary to revise the outfall swale design, the double 12'Wx4'H RCB culvert previously designed to provide the swale outlet to Spring Creek was, as part of the current study, lowered 0.5 feet. The upstream and downstream invert elevations for this culvert are now 4995.5 and 4995.0 ft, msl, respectively,. The remaining culvert design 7