2026-02 Offsite Stability NOAA 24-hr D 25-Year Rainfall=6.68", P2=4.04" Prepared by Dynamic Engineering Printed 2/10/2026 HydroCAD® 10.20-8a s/n 08640 © 2025 HydroCAD Software Solutions LLC Page 11
Summary for Subcatchment 19S: Study Area WQ MTD A-110 (Perv)
Runoff = 0.00 cfs @ 12.38 hrs, Volume= 0.001 af, Depth= 0.66" Routed to Link 18L : Study Area Study Area WQ MTD A-110 (Total)
Runoff by SCS TR-20 method, UH=Delmarva, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.05 hrs NOAA 24-hr D 25-Year Rainfall=6.68", P2=4.04"
Area (ac) CN Description
0.020 39 >75% Grass cover, Good, HSG A
0.020 39 100.00% Pervious Area
Tc (min) Length (feet) Slope (ft/ft) Velocity (ft/sec) Capacity (cfs) Description
1.4 8 0.0125 0.10 Sheet Flow, A-B Grass: Short n= 0.150 P2= 4.04"
0.2 46 0.0380 3.96 Shallow Concentrated Flow, B-C Paved Kv= 20.3 fps
1.3 297 0.0035 3.68 4.52 Pipe Channel, C-D 15.0" Round Area= 1.2 sf Perim= 3.9' r= 0.31' n= 0.011 Concrete pipe, straight & clean
2.9 351 Total, Increased to minimum Tc = 10.0 min
Subcatchment 19S: Study Area WQ MTD A-110 (Perv)
2026-02 Offsite StabilityNOAA 24-hr D 25-Year Rainfall=6.68", P2=4.04"
Prepared by Dynamic EngineeringPrinted 2/10/2026
HydroCAD ® 10.20-8a s/n 08640 © 2025 HydroCAD Software Solutions LLCPage 12
Summary for Pond 17P: Basin A Routing (StormBrixx)
Inflow Area =0.740 ac, 97.30% Impervious, Inflow Depth = 6.28" for 25-Year event
Inflow =3.02 cfs @ 12.19 hrs, Volume= 0.388 af
Outflow =1.06 cfs @ 12.67 hrs, Volume= 0.300 af, Atten= 65%, Lag= 29.0 min
Primary =1.06 cfs @ 12.67 hrs, Volume= 0.300 af
Routed to nonexistent node 14L
Routing by Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.05 hrs Peak Elev= 120.31' @ 12.67 hrs Surf.Area= 3,001 sf Storage= 8,183 cf
Plug-Flow detention time=244.3 min calculated for 0.300 af (77% of inflow) Center-of-Mass det. time=155.0 min (910.0 - 755.0)
VolumeInvertAvail.StorageStorage Description
#1A117.50'0 cf31.63'W × 94.88'L × 3.00'H Field A
#2A117.50'8,729 cf8,999 cf Overall - 8,999 cf Embedded = 0 cf × 40.0% Voids\nACO StormBrixx SD 1 × 384 Inside #1\nInside= 23.7"W × 36.0"H => 5.75 sf × 3.95'L = 22.7 cf\nOutside= 23.7"W × 36.0"H => 5.93 sf × 3.95'L = 23.4 cf\n384 Chambers in 16 Rows
8,729 cf Total Available Storage
Storage Group A created with Chamber Wizard
DeviceRoutingInvertOutlet Devices
#1Primary117.50'15.0" Round Culvert L= 22.0' RCP, groove end projecting, Ke= 0.200 Inlet / Outlet Invert= 117.50' / 117.40' S= 0.0045'' Cc= 0.900 n= 0.013, Flow Area= 1.23 sf
#2Device 1118.81'6.0" Vert. Orifice C= 0.600 Limited to weir flow at low heads
Primary OutFlow Max=1.06 cfs @ 12.67 hrs HW=120.31' (Free Discharge) 1=Culvert (Passes 1.06 cfs of 9.70 cfs potential flow) 2=Orifice (Orifice Controls 1.06 cfs @ 5.38 fps)