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HomeMy WebLinkAboutWATERGLEN PUD - FINAL - 71 93B - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE RELATED DOCUMENTBasil, Some additional internal notes and comments for you regarding the Waterglen P.U.D.: The SWMM subbasin parameters used by Love are not the same as those used in the Cooper Slough Master Plan SWMM model. They apparently used values closed to the newer city standard. For your information, here is a comparison of all three: Impervious n Pervious n Impervious Surface Storage Pervious Surface Storage Max. Infiltration Rate Min. Infiltration Rate Infiltration Rate Decay Rainfall Hyetograph Length CS MP Love City 0.013 0.020 0.020 0.120 0.250 0.250 0.062 0.062 0.100 0.250 0.184 0.300 2.00 0.51 0.51 0.3-0.5 0.50 0.50 0.00115 0.0115 0.0018 3 hrs. 2 hrs. 2 hrs. Because they tend to agree with City standards or are conservative compared to the City standard, they may be appropriate. Mike Grimm had mentioned in his comments that there are several HEC-2 cross sections which are extended. All but one of these extended cross sections corresponds to split flow over Vine Drive. This is normal for the operation of HEC-2 with split flow and is therefore not a problem. I did not give any serious review to the Rational Method or street capacity calculations. However, it seems odd to me that Subbasin D3, with an area of 24.5 acres, would not violate street capacity on Waterglen Drive. Just thought you should be aware of this. CLD 4 houses? On the previous submittal, the swale parallel to the Interstate (swale #1) had very low slopes and some contouring problems. This submittal has no contours shown for this swale. Please provide grading, and if slopes are less than 0.4%, add a concrete trickle pan to direct nuisance flows. Please add the velocities and Froude numbers to the swale summary table on sheets 59 and 67. Please list the inverts in and out, and the grates for the detention pond outlets on sheet 68. On the drainage plans please label the size (feet length) and type (curb, curb chase, sump, etc.) of each inlet or sidewalk break. Do this for example, at the end of G1enLoch Drive, where the Glenbar Ct. flows enter Pond G. on Waterglen Drive where the street inlets drain to the swale, where Gaelic Place crosses Waterglen Place, and others marked on the plans). Please also provide design point calculations (table format is best) showing the 2 and 100 year amounts flowing to each inlet, and the amount captured an bypassing. Please provide calculations and post the results on the plans for the design points noted with redline triangles on the plans. Concrete crosspans will be needed to direct all street flows across intersections. The pan width needs to be wide enough to contain the 2 year flows spread. Please give a concentration/design point for each pond inlet, outlet, and for the concentration point where each drainage sub - basin drains. Please give a summary total of the erosion control cost estimate in the report text showing the escrow amount (150% of the estimated costs). wtrgln2.fin Waterglen Substandard street slopes exist at various places along Waterglen Drive (see redlines on plans). The developed flows along Waterglen Drive appear to exceed the allowable street capacities for the 2 year storm at the intersection with Berwick Lane The developed flows at the south end of Waterglen Drive will definitely exceed street capacities where slopes are a substandard .18 $. Please evaluate and address these and other intersections along this major conveyance. Please also provide a detail section view of the inlet/street/channel interaction at Waterglen Drive where the street flows are captured to the channel; is permanent erosion protection needed? Please evaluate the ponding at these inlets. The development generated flows notwithstanding, this intersection appears to be out of compliance with allowable criteria during the flooding of the major swale. Per your HEC-2 profile 8300, it appears that Box Elder flooding will have a water.depth of 4958.1 feet, however the street there is shown at an elevation of less than 4957 feet. Please provide a larger scale detail drawing to clarify the street elevations and to show the depth and lateral extent of street flooding due to Basin D development and the Box Elder flooding. The swale that carries the Budweiser storm releases to the Slough is not a detained part of Basin A. The flows generated in this swale exceed the allowable releases from pon A using your 0.09 cfs/ac. release rate. Please reevaluate the pond releases to offset this undetained flow. Crosslot flows are still shown for a majority of the project. These are not acceptable. The flow arrows are shown in some cases parallel to the contours. Please contour to redirect the flows between houses and avoid backyard flows crossing to neighboring lots. Please describe and show on the plans how the Basin F flows are to cross Elgin Court and reach Pond F. As presently designed, it appears that a majority of the flows developed in that basin ar developed on the west side of the street, but the pond is east of the cul-de-sac off the east side of Elgin. Post crossing flows on the drainage plans. Please describe and show on the plans how the flows developed along Celtic Lane and Gaelic Place are to cross Waterglen Place and enter the constructed swale. Please also post these flows on the plans. As previously requested, please show on the plans the high water level for the Larimer Weld canal along the west side of your proposed project, and along the north perimeter. Will the water level exceed the required freeboard needed to protect the adjacent Final Drainage Report Checklist Page -3 IV. NOTES/COMMENTS (continued) Note Note/Comment No. 5 The velocities in portions of swale sections 1 and 2 are greater than allowed by criteria. The flow regime in swale sections 4, 11, 12 and 14 are supercritical, or near critical and therefore unstable. Note that this comment is valid assuming the input parameters to the normal depth program are correct. You need to refer to the Fort Collins Criteria Manual as it appears that all Manning's n values (except in swale 1) do not meet criteria. 6 The HEC-2 modeling efforts require considerable documentation to describe in detail the purpose of each model -- we can make inferences but would rather not. The following HEC-2 related comments are provided: The velocities given by HEC-2 at cross -sections 8550 and 8600 are approximately 8.5 fps; riprap is not specified. In addition, the depth of flow in the Boxelder Creek overflow channel exceeds 4 feet at several locations along Vine Drive; this does not meet criteria. Please extend the HEC-2 modeling and floodplain mapping for the Boxelder Creek overflow channel to the northern end of swale section 1.. Several comments related to the split flow modeling are included in the appendix; please check these. The floodplain mapping for both existing and proposed conditions is not commensurate with the split flow results indicated in the models. In addition, the floodplain mapping is incomplete along the southern and eastern boundaries of the major swale where flow splits are not occurring. 7 Please address the additional comments which are given in the report, appendix and Utility Plan set. Final Drainage Report Checklist IV. NOTES/COMMENTS Note No. Page z Note/Comment As a general note, there is little or no documentation of the SWMM and HEC-2 modeling efforts. Since this is a large complex system you are analyzing, substantially more documentation is required to justify your assumptions and to provide an understanding of all methodologies, flow routings and results. Often times unnecessary comments are generated because the reviewers cannot follow the analyses. 1 In the SWMM model, the peak discharge for every conveyance element occurs at the end of the simulation. This may indicate that the hydrographs are still on the rising limb. Please extend the duration of the SWMM model to include the peak for all conveyance elements. 2 The subbasin widths used in the SWMM model are not representative of the proposed drainage patterns. Dividing the subbasin width into the subbasin area produces an average overland flow length of approximately 2,400 feet for the development. An overland flow length about 150 to 200 feet would be more appropriate for a residential development. Flow in streets or swales can then be modeled by a representative conveyance element, as appropriate. As modeled, the efficiency of the runoff collection system (i.e., streets) is drastically under -estimated; this can have a substantial impact on peak runoff values. 3 Correlation is required between the basin id letters given on the sheets and the basin numbers in the SWMM model; several basin to not correspond and it appears that direct rainfall on Cooper Slough (Basin H) is not accounted for in the SWMM model. In addition, several off -site areas appear to contribute flow to the site, but are not included in the hydrologic analyses. 4 Several comments are provided concerning the SWMM modeling of the detention ponds, please make the appropriate modifications to your analyses: Defining an operational pipe in conjunction with a storage -discharge rating curve may double account or otherwise misrepresent pond releases; as defined, it is probable that the ponds are not modeled correctly. Modify or provide detailed documentation which justifies the given methodology. The "two point" rating curves given in the SWMM model for the detention ponds do not accurately reflect the physical operation of the ponds. The rating curves allow pond releases immediately with any incremental increase in storage volume. As designed, the ponds will not have any measurable discharge (as you have defined) until the water surface reaches the inlet grate. More physically accurate curves are required. , . - a ro. ' CITY OF FORT COLLINS FINAL DRAINAGE REPORT CHECKLIST I Name of Project: UA-rr ' (:Som m f I Submittal Number: I Reviewed by: Engineer: Lrm Date Received: LCILA74 Submittal Package: I. Drainage Report Utility Plan ❑ Plat Drawings Name of project alb date of preparation Vicinity map Scale and true north symbol Location of boundary lines of prcject,`fi€ streets, railroads, easements and lot lines Location and size of all on -site drainage including proposed outlets, detention poi drainageways, and side and rear lost eas Location and size of all off -site Floodplain and floodway Phone Number: (3a3� 44-o - 343-i Date Completed: 11 I + 1-7j of way, easements Delineation of existinewetland/wildlife areas Designation ofAM streets and other rights of way, including n,afnes and dimensions JV Grading and Drainage Plan ❑ Landscaping and Site Plan ❑ Erosion Control Plan See See Note Sheet Yes No No. N/A No. 0