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HomeMy WebLinkAboutMinutes - March 28, 2023 SSLodi’s Storm Drainage System and Recent Storm Events Mills Ave & Tokay St (Oct 2021) Storm Drainage & Recent Events Overview •Causes of Street Flooding •Rain Event Terminology •Lodi’s Storm Drainage System •Recent Storm Events •Specific Areas Prone to Street Flooding •Potential Projects to Minimize Impacts •Questions General Street Flooding Causes •Pipe / Inlets Blocked (Debris, Leaves, Gravel Bags, etc.) •Rain Flow is more than the Pipe Capacity •Nowhere for the Water to Go •Basin Full •Flow is Higher than Pump Station Can Handle Storm Drainage & Recent Events Rain Event Terminology •Frequency & Duration •Frequency Curves = % Chance Happening •5-Year = 20% (1/5) Chance / Year •100-Year = 1% (1/100) Chance / Year •Developed by Historical Data & Models •Duration •“48-Hour” = Amount of water dropped over the Duration •100-Year, 48 Hour Rain Event •Different than 100-Year River Floodplain Storm Drainage & Recent Events Rain Event Terminology Storm Drainage & Recent Events 4.8” 48 Hr Lodi’s Storm Drainage System Storm Drainage & Recent Events WID Outlets 17 River/Lake Outlets (#s) 12 Basins (Letters) 2 WID Outlets Lodi’s Storm Drainage System •Pipe Sizing •Older Areas (Pre-2000): 2-Year Storm Flows w/ Full Basin •Newer Areas: 2-Year Full Basin 5-Year Empty Basin Storm Drainage & Recent Events 1’ 1’ 2-Year Full Basin 5-Year Empty Basin Full Basin Empty Basin Higher (4.8”) Lodi’s Storm Drainage System •Basin Sizing •100-Year, 48-Hour Event •Pre-1980 Basins •Reduction for Outflow •Pump Stations •WID Agreement •60 CFS / Location •160 CFS Total (Currently 2 Connections, Ultimately 3) Storm Drainage & Recent Events Lodi’s Storm Drainage System •Newer Subdivisions (Since 2013) Require “Street Breakovers” in Design •Even if Streets Flood, the Houses Shouldn’t “Bathtub & Soap Dish Comparison” Street Breakover Elevation Lowest House Elevation Storm Drainage & Recent Events Pause for Questions Rain Event Terminology or Lodi’s Storm Drainage System Storm Drainage & Recent Events Recent Storms •Short Intense •December 10, 2022 •January 14, 2023 •High Volume •October 24-25, 2021 •December 30-31, 2022 Storm Drainage & Recent Events Short Intense Storms Storm Drainage & Recent Events Expect short-term street flooding High Volume Storms Storm Drainage & Recent Events Expect short-term street flooding Expect longer street flooding 48 0.0'' 0.5'' 1.0'' 1.5'' 2.0'' 2.5'' 3.0'' 3.5'' 4.0'' 4.5'' 5.0'' 5.5'' 6.0'' 6.5'' 7.0'' 10:00 PM 6:00 AM 2:00 PM 10:00 PM 6:00 AMRainfallTime (Saturday -Sunday -Monday) 100-Year 48 Hour Rainfall Cumulative Rainfall Hourly Rainfall October 2021 Storm 4.8” @ ~9:00PM (22 Hours) ~6.6” in 32 Hours “Atmospheric River” Storm Drainage & Recent Events October 2021 Storm (DeBenedetti) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110% 120% 130% 140% 150% 0.0'' 0.5'' 1.0'' 1.5'' 2.0'' 2.5'' 3.0'' 3.5'' 4.0'' 4.5'' 5.0'' 5.5'' 6.0'' 6.5'' 7.0'' 10:00 PM 6:00 AM 2:00 PM 10:00 PM 6:00 AM Basin StorageRainfallTime (Saturday -Sunday -Monday) Basin Storage vs Cumulative Rainfall 100-Year 48 Hour Rainfall Hourly Rainfall (in) Cumulative Rainfall DeBenedetti (G Basin) 50%-120% in 5 Hours Storm Drainage & Recent Events October 2021 Storm •Timing (Length of Storm) Matters •Kofu •Beckman •Vinewood •Henry Glaves •Salas 4.8” @ 22 Hours ~150% Volume 6.6” @ 32 Hours ~200% Volume Storm Drainage & Recent Events Storm Drainage & Recent Events October 2021 Storm •How’d the Basins Fare? •Kofu (A-1)2.0’140% •Beckman (A-2)2.5’150% •Vinewood (B-1)2.5’170% •Henry Glaves (B-2)1.0’130% •Pixley (C)4.5’150% •Salas (D)1.0’120% •Peterson (E)1.0’120% •Rose Gate 1 (F-1)N/A N/A •DeBenedetti (G)3.0’145% Above HW % Full Flooding Photos Kofu (Oct 2021) DeBenedetti (Oct 2021) Flooding Photos Vinewood Park (Oct 2021) Mills & Tokay (Oct 2021) Vinewood Park (Oct 2021)1711 W Tokay (Oct 2021) Flooding Photos Lower Sacramento (Oct 2021) Lower Sacramento (Dec 2022) Ham Lane (Oct 2021) Cabrillo Circle (Oct 2021) Flooding Photos Vineyard Terrace (Dec 2022) Vineyard Terrace (Dec 2022) Vineyard Terrace (Dec 2022) Pause for Questions Recent Rain Events Storm Drainage & Recent Events Flood-Prone Areas Storm Drainage & Recent Events •100+ Flood Calls in Major Events •Short Intense Storm •Spread Out •High Volume Storm •Near Basins •Other Known Areas (Without Many Calls) Specific Flood-Prone Areas Storm Drainage & Recent Events •Vinewood (B-1) •DeBenedetti (G) (Vineyard Terrace) Primarily “High Volume” Events (Basin is Full) Both Types of Events Specific Flood-Prone Areas Storm Drainage & Recent Events •Why does this happen? •High Volume Storms = Basins Too Full 1’ Street Flooding Design High Volume Storm Specific Flood-Prone Areas Storm Drainage & Recent Events •Short Intense Storms •Design Storms •Frequency = More Complicated Specific Flood-Prone Areas Storm Drainage & Recent Events •Short Intense Storms 1’ 1’ 2-Year Full Basin 5-Year Empty Basin Full Basin Empty Basin > 2-Year Design Flow > 5-Year Design Flow Street Flooding Street Flooding Specific Flood-Prone Areas Storm Drainage & Recent Events •Short Intense Storms Design Flow = A x I x C •(A) Area “How much area is going to that specific inlet or pipe” •(I) Rainfall Intensity “How much water is falling in a period of time” •(C) Runoff Coefficient “How much water is running off the site” Specific Flood-Prone Areas Storm Drainage & Recent Events •Short Intense Storms Design Flow = A x I x C •(I) Rainfall Intensity •Time of Concentration •Length of Time from Furthest Point to a Specific Inlet/Pipe •Shorter Time = Higher Design Intensity •What Impacts the Time of Concentration? Time of Concentration Storm Drainage & Recent Events •Type of Surface •Roof •Back yard •Front yard Time of Concentration Storm Drainage & Recent Events •Type of Drainage Collection •Over-Land •Area Drains •Roof Drains •Outlet Location Rainfall Intensity Storm Drainage & Recent Events •Does this Make of a Difference? •City’s Design Standard: 25 Minutes (Res) •If Tc is 5 minute less, the design Intensity (I) is up to 16% higher 1.09 1.26 Rainfall Intensity Summary Storm Drainage & Recent Events •Faster it Gets There = Higher the Flows Runoff Coefficient Storm Drainage & Recent Events •Design Flow = A x I x C •(C) Runoff Coefficient •Ratio of rainwater runs off the site •Higher C Factor = Higher Flow into Inlet/Pipe •What Impacts the Runoff Coefficient? Land Uses Surface Types 0.4 Min. (1963-2019) 0.8 = 80% Running Off Runoff Coefficient Storm Drainage & Recent Events •(C) Runoff Coefficient Example x = Check Larger Area: Composite C = 0.73 > “0.4 -0.6” x =x =x =Bldg Conc Pvmt Land Conc Runoff Coefficient Storm Drainage & Recent Events •Why So High? •Trend of Larger Houses on Smaller Lots •Smaller Front & Rear Yard Setbacks over Time •Concrete Back Yards •Concrete Front/Side Yards •Synthetic Grass Runoff Coefficient Storm Drainage & Recent Events •Not Unique to One Location •Analysis 20 Residential Locations (1950-2021) •Style of Development Over Time •+10% 1950s Into 1960s, Steady from 1960s through 1990s •+5% Early 2000s, +5% ~2017 •Increase in Hardscape over Time. Rarely Opposite 10% 5%5% Storm Drainage Flows Storm Drainage & Recent Events •What does this all mean? •Rainfall Intensity (I) •Tc is 5 Minutes Shorter •16% Higher Intensity •Runoff Coefficient (C) •Design = 0.50, Actual = 0.73 •46% Higher •Design Flow = A x I x C •(A) Area •1.16 (I) Rainfall Intensity •1.46 (C) Runoff Coefficient •Actual Flow almost 70% Higher Than Design Storm Drainage Flow Summary Storm Drainage & Recent Events •Faster Water Gets There = Higher the Flows •The More Water Runs Off = Higher the Flows Pause for Questions Specific Flood Prone Areas or Flow Calculations Storm Drainage & Recent Events Potential Projects Storm Drainage & Recent Events •So What Now? •Increase Awareness •Reviewed Areas Most-Impacted by Major Storms •Created a List of Potential Projects •Will Return to Council With Full List / Timing / Costs •Sample of Potential Projects by Location Potential Projects Storm Drainage & Recent Events •Kofu Park (A-1 Basin) •Add Passive Connection to Skate Park Area •Adds 23% Basin Capacity (without Flooding Ham Lane) •Vinewood Park (B-2 Basin) •Minor Pump Station Improvements •Increase the Pump Capacity (Drain the Basin Quicker) •Shady Acres Pump Station •Minor Modifications •Increase Pumping Capacity Potential Projects Storm Drainage & Recent Events •Pixley Park (C Basin) •Square-Off •Adds 58% Basin Capacity •Rose Gate Park (F-1 Basin) •Deepen Basin (~1.5’) •Adds 30% Capacity •Rose Gate 2 Basin (F-2) •Deepen Basin •Adds 13% Capacity $$$ Potential Projects Storm Drainage & Recent Events •DeBenedetti Park (G) •Add Century Outfall •Reduce Pressure on the Century Line •Deepen Middle Area •Add 6% Capacity •Vineyard Terrace •Additional Pipe Connection •Reduce Pressure on the onsite storm drainage system Questions?