Revised 1/2023 3/20/2023 3:22 PM
For information regarding this Agenda please contact:
Olivia Nashed
City Clerk
Telephone: (209) 333-6702
A. Call to Order / Roll Call
B. Topics
B-1 Receive Information on Lodi’s Storm Drainage System and Recent Storm Events (PW)
C. Comments by Public on Non-Agenda Items
THE TIME ALLOWED PER NON -AGENDA ITEM FOR COMMENTS MADE BY THE PUBLIC IS LIMITED TO FIVE MINUTES.
Public comment may only be made on matters within the Lodi City Council's jurisdiction (Government Code Section 54954.3, Lodi City Council Protocol Manual Section 6.3l) . The Council cannot take action or deliberate on items that are not on this agenda unless there is an emergency and the need t o take action on that emergency arose after this agenda was posted (Government Code Section 54954.2(b)(2)). All other items may only be referred for review to staff or placement on a future Council agenda.
If you wish to address the Council, please refer to the Notice at the beginning of this agenda. Individuals are limited to one appearance during this section of the Agenda.
D. Adjournment
Pursuant to Section 54954.2(a) of the Government Code of the State of California, this agenda was posted at least 72 hours in advance of the scheduled meeting at a public place freely accessible to the public 24 hours a day.
______________________________
Olivia Nashed
City Clerk
LODI CITY COUNCIL
Carnegie Forum
305 West Pine Street, Lodi
Notice Regarding Public Comments
Public Comment may be submitted in the following ways:
• In-person
• Email – [email protected]
Received no later than 4:30 p.m. on the business day prior to the meeting. • Mail – City Clerk’s Office, P.O. Box 3006, Lodi, CA 95241 • Hand delivered to: City Clerk’s Office, 221 W. Pine Street, Lodi, CA 95240 Received no later than 4:30 p.m. on the business day prior to the meeting
Public comment received via email, mail, or hand delivery will be provided to the City Council and included in the official minutes record of the meeting, but will not be read aloud at the meeting.
AGENDA – Shirtsleeve Session
Date: March 28, 2023
Time: 7:00 a.m.
All staff reports or other written documentation relating to each item of business referred to on the agenda are on file in the Office of the City Clerk, located at 221 W. Pine Street, Lodi, and are available for public inspection. Agendas and staff reports are also posted on the City’s website at www.lodi.gov . If requested, the agenda shall be made available in appropriate alternative formats to persons with a disability, as required by Section 202 of the Americans with Disabilities Act of 1990 (42 U.S.C. Sec. 12132), and the federal rules and regulations adopted in implementation thereof. To make a request for disability-related modification or accommodation contact the City Clerk’s Office as soon as possible and at leas t 72 hours prior to the meeting date. Language interpreter requests must be received at least 72 hours in advance of the meeting to help ensure availability. Contact Olivia Nashed at (209) 333- 6702. Solicitudes de interpretación de idiomas deben ser recibi das por lo menos con 72 horas de anticipación a la reunión para ayudar a asegurar la disponibilidad. Llame a Olivia Nashed (209) 333-6702.
Meetings of the Lodi City Council are telecast on SJTV, Channel 26. The City of Lodi provides live and archived webcasts of regular City Council meetings. The webcasts can be found on the City's website at www.lodi.gov by clicking the meeting webcasts link.
Members of the public may view and listen to the open session of this meeting at www.facebook.com/CityofLodi/.
AGENDA ITEM B-01
COUNCIL COMMUNICATION
APPROVED: ________________________________
Stephen Schwabauer, City Manager
\\cvcfilv02\pubwks$\WP\COUNCIL\2023\CC Storm Drain System SS 032823.docx 3/20/2023 AGENDA TITLE: Receive Information on Lodi’s Storm Drainage System and Recent Storm Events M
EETING DATE: March 28, 2023
P
REPARED BY: Public Works Director
RE
COMMENDED ACTION: Receive information on Lodi’s storm drainage system and recent storm events.
B
ACKGROUND INFORMATION: Over the past few years, the City has experienced several “atmospheric river events”. These once rare, but significant rainfall events have tested the City’s existing network of pipes, basins and pump stations on a more frequent basis.
S
taff will provide Council with an overview of the City’s storm drain system and current design standards; outline the impacts of more compact development on the storm drain system; and discuss potential long-term solutions for addressing climate change as it relates to providing appropriate storm drain service.
F
ISCAL IMPACT: Not applicable
F
UNDING AVAILABLE: Not applicable
________________________________________
C harles E. Swimley, Jr.
Public Works Director
Lodi’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 AM
Rainfall
Time (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 Storage
Rainfall
Time (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?