OC Watersheds Newport Bay Sediment TMDL
In March 1999 the Santa Ana Regional Water Quality Control Board approved a sediment
total maximum daily load (TMDL) for the Newport Bay watershed to address water quality
impairment due to excessive sedimentation. The TMDL for sediment requires implementation
and maintenance of sediment control measures aimed at ensuring that existing habitat
acreages of Upper Newport Bay are not significantly changed and sediment discharges
in the watershed are reduced by 50% over a multi-year period. The long term goal
of the sediment TMDL is to reduce the frequency of dredging Upper Newport Bay to
once every 20 to 30 years.
Quantifiable targets of the TMDL are to:
- Reduce the annual average sediment load from a total of 250,000 tons per year to
125,000 tons per year, thereby reducing the sediment load to Newport Bay to 62,500
tons per year and limiting sediment deposition in the drainages to 62,500 tons per
year.
- Maintain the existing acreages of aquatic, wildlife, and rare and endangered species
habitat in the Bay
- Maintain a minimum depth of 7 feet below mean sea level in Units I and II of the
Bay
- Maintain 50% available storage capacity levels of the in-channel and foothill basins.
In November 1999 the Santa Ana Regional Water Quality Control Board subsequently
adopted Monitoring and Reporting Program No. 99-74 which requires monitoring, surveys,
and reporting in accordance with the requirements of the sediment TMDL. The sediment
monitoring and maintenance program consists of two study area elements: (1) the
Upstream Monitoring Element which includes those activities performed in the San
Diego Creek watershed upstream of Jamboree Road Bridge and in the Santa Ana-Delhi
Channel, and (2) the Newport Bay Monitoring Element which includes those activities
performed in Upper Newport Bay.
The Upstream Monitoring Element consists of monitoring and maintaining the available
capacities of three in-channel basins along San Diego Creek, seven foothill basins,
and the collection of suspended sediment samples during dry flow and storm flow
conditions and streamflow data from eight monitoring stations.
The Newport Bay Monitoring Element consists of conducting vegetative and bathymetric
surveys as needed, removal of sediment from the in-bay basins as needed, and fluvial
sediment and flow monitoring during storm events.
An annual report is submitted to the Santa Ana Regional Water Quality Control Board
by November 15 of each year verifying that the in-channel and foothill basins have
at least 50% design capacity available for the upcoming storm season. The TMDL Annual
Report (a compilation of sediment monitoring data and TMDL compliance analysis)
is to be submitted by February 27 of each year.
In general, the available data suggests that sediment loads in the Newport Bay/San
Diego Creek watershed have been reduced significantly from rates recorded in the
pre-TMDL period and that the target reduction is being attained. The suspended sediment
discharge to Newport Bay for the July 1, 2008 through June 30, 2009 period as calculated
from the San Diego at Campus Drive, Santa Ana-Delhi at Irvine Avenue, and Bonita
Creek Channel at MacArthur Blvd. monitoring stations was 17,135 tons. The suspended
sediment load average for the ten-year period (2000-2009) since approval of the
TMDL as measured at the San Diego Creek at Campus monitoring station is approximately
42,308 tons per year. The San Diego Creek at Campus monitoring station represents
the majority (~90-98%) of sediment discharges to Newport Bay, depending on the water
year.
TMDL Resource Links
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