RE: Final Drainage Letter: Northwest Aurora Alley Improvements 2016

Transcription

1 April 12, 2016 Mr. Craig Perl, P.E. Senior Engineer City of Aurora Public Works Department E. Alameda Parkway Aurora, CO RE: Final Drainage Letter: Northwest Aurora Alley Improvements 2016 Dear Mr. Perl, This Final Drainage Letter is submitted in support of the proposed drainage inlet and storm sewer to be installed in Alley 223. Alley 223 is bounded by Dallas St, Dayton St, 12 th Avenue and 13 th Avenue to the west, east, south and north respectively. Description of Existing Conditions Alley 223 does not currently drain properly due to an existing sump approximately 200 ft north from the alley s southern boundary (at 12 th Avenue). The area in question is bounded by asphalt parking areas on either side for multi-family residential buildings. A history of ponding in this sump is evident in a small area drain on private property to the west of the alley. This area drain pipes out to the curb flowline of Dallas and was most likely installed by building maintenance. While this drain is sufficient for nuisance flows, it does not appear to have capacity to convey a storm event of any significance. Description of Proposed Conditions The relatively flat grades observed in the alley result in an inability to drain this sump out to the 12 th or 13 th Avenue infrastructure by surface means. Therefore, a Double Type 13 Valley Inlet is proposed in the sump to alleviate the drainage issue. An 18 RCP sewer pipe will then connect to the storm sewer infrastructure located at the intersection of Dayton & 12th. The catchment area for this new inlet was calculated to be approximately 0.72 Acres and a imperviousness of 80% was used for the classification of Residential: Apartments per the City of Aurora Drainage Manual. The 2- and 100-year storms were analyzed and their discharges found to be 1.5 and 5.2 cfs respectively. The proposed 18 RCP has a normal flow capacity of 8.6 cfs at the designed 0.7% pipe slope. Finally, the hydraulic grade lines (HGL) were calculated using assumed tailwater

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3 PROPOSED CONNECTION TO STORM SEWER PROPOSED BASIN CATCHMENT AREA

4 REVISIONS: NO. DESCRIPTION BY DESIGNED BY: 14th AVE CAD BY: CHECKED BY: PROJECT No.: 13th AVE 12th AVE CLINTON ST DALLAS ST DAYTON ST EMPORIA ST KEY MAP NTS ALLEY 223 DRAINAGE BASIN EXHIBIT

5 INLET IN A SUMP OR SAG LOCATION Project = Inlet ID = 2016 NWA Alley Improvements Double Type 13 Valley Inlet H-Curb W W P H-Vert Lo (C) Wo Lo (G) Design Information (Input) MINOR MAJOR Type of Inlet Inlet Type = CDOT/Denver 13 Valley Grate Local Depression (additional to continuous gutter depression 'a' from 'Q-Allow') a local = inches Number of Unit Inlets (Grate or Curb Opening) No = 2 2 Water Depth at Flowline (outside of local depression) Ponding Depth = inches Grate Information MINOR MAJOR Override Depths Length of a Unit Grate L o (G) = feet Width of a Unit Grate W o = feet Area Opening Ratio for a Grate (typical values ) A ratio = Clogging Factor for a Single Grate (typical value ) C f (G) = Grate Weir Coefficient (typical value ) C w (G) = Grate Orifice Coefficient (typical value ) C o (G) = Curb Opening Information MINOR MAJOR Length of a Unit Curb Opening L o (C) = N/A N/A feet Height of Vertical Curb Opening in Inches H vert = N/A N/A inches Height of Curb Orifice Throat in Inches H throat = N/A N/A inches Angle of Throat (see USDCM Figure ST-5) Theta = N/A N/A degrees Side Width for Depression Pan (typically the gutter width of 2 feet) W p = N/A N/A feet Clogging Factor for a Single Curb Opening (typical value 0.10) C f (C) = N/A N/A Curb Opening Weir Coefficient (typical value ) C w (C) = N/A N/A Curb Opening Orifice Coefficient (typical value ) C o (C) = N/A N/A MINOR MAJOR Total Inlet Interception Capacity (assumes clogged condition) Q a = cfs WARNING: Inlet Capacity less than Q Peak for Minor Storm Q PEAK REQUIRED = cfs Design Point 1.xlsm, Inlet In Sump 3/10/2016, 5:11 PM

6 Manning's Intensity, i = (28.5*P)/(10+Tc)^0.786 Page 1 of 2 "n" values: Fr P 12-Apr-16 RCP Rainfall Curves: Aurora, CO DIP Units: English CMP HDPE STORM SEWER COMPUTATIONS PVC Project: NWA Alley Imporvements 2016 Designed: MWK Date: 4/12/16 Project No: Checked: MWK Date: 4/12/16 LOCATION SUBAREA DATA PIPE DATA DESIGN FLOW PIPE FROM TO Area "C" CxA CxA T c T c Fr "I" Q A Mat # of Type Span Hgt L Slope n Q cap Inverts Upper End % of Q A d V A t ID Ac *Note 1 Sum min Sum Yr in/hr cfs Brl's in in ft % cfs Upper Lower Grate Cover Cap cfs ft fps min MINOR STORM - 2-YEAR EVENT 2 IN-1 MH RCP 1 C MH-2 MH RCP 1 C MAJOR STORM YEAR EVENT 2 IN-1 MH RCP 1 C MH-2 MH RCP 1 C Notes: 1) Runoff coefficients based on 80% Impervious as defined by "Residential: Apartments" in Table 1 of the City of Aurora Drainage Manual. N:\PWD\projects\2016 Projects\ Northwest Alley Improvements\Reports\Drainage\[pipes.xls]Design

7 12-Apr-16 Page 2 of 2 Upper EGL = Lower EGL + Hf Inlet EGL = Upper EGL + Ht Inlet WSE = Inlet EGL - v 2 /2g Units: English HYDRAULIC GRADE LINE COMPUTATIONS Project: NWA Alley Imporvements 2016 Designed: MWK Date: 4/12/16 Project No: Checked: MWK Date: 4/12/16 LOCATION Friction Loss in Pipe Structural Losses Lower Lower Exit Loss Entr. Loss Bend Loss Total Inlet Inlet Rim F.B. PIPE FROM TO EGL WSE Mat # of Type Span Hgt Q V H v L Flow S f H f Upper K i H i K o Ho Ang K b H b H t EGL WSE Elev. ID Brl's in in cfs fps ft ft Type % ft EGL ft ft deg ft ft ft MINOR STORM - 2-YEAR EVENT 2 IN-1 MH RCP 1 C BACK 0.59% MH-2 MH RCP 1 C BACK 0.14% Note: Downstream HGL for minor 2-year event is assumed to be the spring line of the existing 21" storm pipe. MAJOR STORM YEAR EVENT 2 IN-1 MH RCP 1 C BACK 0.33% MH-2 MH RCP 1 C FULL 0.22% Note: Downstream HGL for major 100-year event is assumed to be equal to the crown of the existing 21" storm pipe, and thus the crown of the outlet pipe. N:\PWD\projects\2016 Projects\ Northwest Alley Improvements\Reports\Drainage\[pipes.xls]Design