AGENDA
ITEM
ADDITIONAL BACKUP INFORMATION
4 Dynamic ENGINEERS CONSULTING
January 23, 2024
Esperanza Colio Warren
City Manager
City of Calexico
608 Heber Ave,
Calexico, CA 92231
RE: Preliminary Report of the 1/22/2024 Storm Event
A major winter storm hit Southern California including Imperial County and parts of Mexicali (Mexico) on Monday January 22, 2024. The City of Calexico and the City of Mexicali experienced intense rainfall for most of the day. Portion of the City of Mexicali drains to the New River and crosses the international boundary into the United States. This intense rainfall event triggered the New River flow to rise significantly and out of control at the international crossing. The City of Mexicali storm runoff in the New River is concentrated at the international crossing (New River).
The United States Geological Survey (USGS) has a flow monitoring station at the New River, approximately 200 feet south of the Second Street bridge which provides data every 15 minutes. USGS 10254970 New River at International Boundary at Calexico indicates the peak flow of 822 CFS, which is significantly greater than the normal flow experienced earlier in the morning, and for the past several days of 70 CFS.
It must also be noted that wastewaters from Mexico were purposely bypassed to the New River of undetermined amount, constituent loading, and unknown length of time. The city was advised of this in an email communication by the International Boundary and Water Commission (IBWC) on behalf of the Mexicali office of CESPM. This inflow of wastewaters from Mexico started at 9:44 am from Mexicali Drain 134, then additional flows at 11:00 am from Puente Quintano Roo Gate to Pumping Plant #1 50% closed due to their treatment capacity limit, then at 11:15 am they added more bypass from their Pumping Plant #4. In essence, more than storm water flows contributed to this flooding. A graph shown on the next page shows the incremental increase of storm water flows and other input mentioned, into the New River at the International Border with Mexico which discharges into the US at the project site. 2415 Imperial Business Park Dr., Suite B - Imperial, CA 92251 - Phone: (760) 545-0162 - Fax: (760) 545-0163 Dynamic ENERG
7 days 30 days 1 year
New Rat International Boundary
at Calexico CA - 10254970
January 16, 2024 - January 23, 2024
Discharge, cubic feet per second
822 ft3/s - Jan 22, 2024 02:45:00 PM PST
400-
200°
Jen 17 Jan 18 Jen 19 Jan 20 Jan 21 Jar 22 Jan 23
IMPORTANT Datamay be provisional
Show legend v
Value Status
This storm event caused major damage to the construction of the New River Improvements Project.
Construction for this project started summer 2023 and it has been ongoing. The majority of the damage happened at the diversion structure which is located along the New River approximately 1,000 feet from the international boundary. The rise in flow and water level in the New River caused the water to enter into the construction site. The construction site for the diversion structure has been guarded with metal sheet piles (cofferdam) and has continuous dewatering wells to keep water from entering the construction site.
During the rise of the New River water level and flow, the construction site at the diversion structure flooded. See images below showing pictures before the rainfall even and during the rainfall event:
2415 Imperial Business Park Dr., Suite B - Imperial, CA 92251 - Phone: (760) 545-0162 - Fax: (760) 545-0163 Dynamic CONSULTING
ENGINEERS
Images Prior to Storm Event of 1/22/2024
2415 Imperial Business Park Dr., Suite B - Imperial, CA 92251 - Phone: (760) 545-0162 - Fax: (760) 545-0163 Dynamic CONSULTING
ENGINEERS
Images During Storm Event of 1/22/2024
2415 Imperial Business Park Dr., Suite B - Imperial, CA 92251 - Phone: (760) 545-0162 - Fax: (760) 545-0163
CONSULTING
Dynamic
ENGINEERS
2415 Imperial Business Park Dr., Suite B - Imperial, CA 92251 - Phone: (760) 545-0162 - Fax: (760) 545-0163
CONSULTING
Dynamic
ENGINEERS
Aerial Image taken 1/23/2024
As shown in the pictures, the water from the New River breached into the construction zone. The damages to the construction site are currently being evaluated and will continue to be evaluated as more access to the site becomes is available.
2415 Imperial Business Park Dr., Suite B - Imperial, CA 92251 - Phone: (760) 545-0162 - Fax: (760) 545-0163 Dynamic CONSULTING
ENGINEERS
Preliminary site assessment after storm event:
Damages: The following project features have been noted as requiring mitigation or repairs for construction to re-commence to the level prior to the rainfall event. They are organized by the three key project categories:
New River Diversion Structure
New River Diversion Channel area - as mentioned, the New River overtopped the steel sheet piles which compose the cofferdam which allowed workers to grade, compact soils, install steel reinforcement and form for concrete lining, wet well, and walls within the channel area. The New River temporary diversion during this construction was also compromised. During the storm event, the New River split into two channels on each side of the cofferdam, as well as overtopping the cofferdam. It created a new channel along the east side of the cofferdam and compromised the integrity of the temporary diversion channel on the west side of the cofferdam, including damages to the temporary bridge that was needed to access the cofferdam over the diversion channel.
Repairs to the diversion structure construction site will include but will not be limited to:
• Site Clean Up
• Reconstruct Access to the diversion structure construction site • Dewater standing water in the diversion structure site • Assess stability of Metal Sheet Piles
• Reset dewatering wells and pumps
• Regrade areas around cofferdam
• Assess condition of base material placed (may need to be removed and replaced) • Assess condition of recently poured concrete structure • Assess condition of recently installed reinforcing bars for structure • Regrade (reconstruct) channel slopes
Estimated Cost: $550,000.00
2415 Imperial Business Park Dr., Suite B - Imperial, CA 92251 - Phone: (760) 545-0162 - Fax: (760) 545-0163 Dynamic CONSULTING
ENGINEERS
Pump Back System
Portion of the Calexico WWTP drains stormwater runoff into the area of work where the pump back building pad and wet well is located. This is a localized area, but erosion of the banks along the south and east sides added soil material into the area.
Estimated Cost: $40,000.00
72" Bypass Pipeline
This is a 1.5-mile alignment from the diversion channel, northwest and parallel with the New River south bank area where it will discharge to the New River with a new outlet structure. The rainfall caused flooding along the area which will take some time to dry out before any heavy equipment and work can take place on it. The westerly slope area also will need some time to dry out. The immediate concern is that the 72" pipe deliveries from the manufacturer are ongoing, and alignment is needed for pipe layout and stockpile.
Another component is the 30" sewer line crossing which was planned for an early February sewer bypass to replace portion of clay pipe with PVC pipe to install the project 72" through the area. This is needed to complete the west slope grading and hauling of materials across the sewer line. During the storm event, sewer flows were found to be leaking from one of the manholes.
Sewer line replacement work will be delayed until the work area is stable. This will cause delays in the installation of the 72 inch pipe and incur overhead and delay costs.
Estimated Cost: $800,000.00
Project Administration, Engineering and Construction Inspections Additional Cost The reconstruction of the diversion structure could take approximately 6 to 8 weeks. Inspections will be needed for the reconstruction of the diversion structure work.
Estimated Cost: $85,000.00
If you have any questions, please do not hesitate to contact me at 760) 545-0162.
Respectfully,
Cut Bet
Carlos Beltran, P.E.
Construction Manager
Dynamic Consulting Engineers, Inc.
2415 Imperial Business Park Dr., Suite B - Imperial, CA 92251 - Phone: (760) 545-0162 - Fax: (760) 545-0163