2026 02 12 Crestmont CC and Eagle Rock Ave Stormwater Management Report

Ancillary 1 (m) 2 3 Shape / Type Rectangular Exfiltration, in/hr 1.50** Crest Elevation, ft 539.4 Crest Length, ft 2.5 Angle, deg Weir Coefficient, Cw 3.3 m = Flows through Culvert, i = Independent **Exfiltration extracted from outflow hydrograph. Rate applied to contours. Stage-Discharge 542 5 541 4 540 3 539 2 538 1 537 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Discharge (cfs) Top of Pond 2-yr Pond Outflow

EMERGENCY SPILLWAY CALCULATIONS

SMALL-SCALE BIORETENTION BASIN 1

Basin Emergency Spillway Basin: SSBB-1 Project: 101049802 The basin will use a spillway over the proposed berm to serve as a means of emergency overflow. Date: 10/17/2025 The spillway has been designed to convey the 100-year storm event design flow entirely through the spillway with a maximum flow depth. The following calculations demonstrate the adequacy of the spillway: 1. Qreq for the 100yr + 50% Flow = 22.70 CFS z= 3.00 100-yr Elev. = 536.73 2. Spillway Capacity = Qdesign OCS Grate Elevation = 537.75 C = Weir Coefficient = 3.00 L = Weir Length = 62.00 H = Flow Depth = 0.25 Freeboard = 1.00

low Depth = 0.25 Freeboard = 1.00 3/2 Q = CLH Q (cfs) = 23.25 23.25 > 22.70 GOOD 3. Top of the Crest Elevation = 537.75 4. Top of the Berm Elevation = 539.00 Top Width (ft) = 69.50 AREA (SF)= 15.69 Freeboard = 1.00 VELOCITY (ft/s)= 1.45 Top of the Bank = 539.00 1 538.00 Depth = 0.25 Top of the Crest = 537.75 z= 3 100-yr Elev. = 536.73

Freeboard = 1.02 Length = 62.00 Shear Stress Calculation Variables τd = 62.4 (d*S) Vmax C350 Shear Stress Capacity 12 lb/ft2 Channel Bed Slope S 0.33 ft/ft Vmax C350 Maximum Allowable Velocity 20 ft/sec Depth of Water d 0.50 ft τd = 10.296 lb/ft2 Pass VMAX = 1.45 ft/sec Pass Over Spillway Filter Filter Velocity Median Stone d50 Size Thickness *d (ft/s) Size (in) (in) NSA-No. NSA-No. (in) d 1.45 C350 N/A N/A N/A N/A *d =

N/A N/A *d = 1.5 times the maximum stone diameter but not less than 6 inches. Discharge Curve 25.00 Discharge (CFS) 23.25 20.00 15.00 15.10 15.10 10.00 11.49 11.49 8.22 8.22 5.00 5.34 5.34 1.03 2.91 2.91 1.03 0.00 0.00 0.00 537.75 537.78

0.00 537.75 537.78 537.81 537.84 537.88 537.91 537.94 538.00 537.94 537.91 537.88 537.84 537.81 537.78

537.78 537.75 Elevations (FT) \\langan.com\data\PAR\data8\101049801\Project Data\_Discipline\Site Civil\Stormwater\Eagle Rock Emergency Spillway Worksheet 10/21/2025 @ 3:47 PM

SMALL-SCALE BIORETENTION BASIN 2