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.