Environmental Engineering Reference
In-Depth Information
hardness and is infl uenced by the slightly saline water table (less than 2% salinity).
Prior to the 1960s, San Diego Creek was not connected directly to Newport Bay,
but an engineered fl ood control system was constructed within the watershed making
the connection permanent. Flows now enter Newport Bay through San Diego Creek
throughout the year. San Diego Creek currently has a mean base fl ow rate of
approximately 12 cubic feet second (cfs). Storm events can increase this daily fl ow
to over 9,000 cfs. The Upper Bay's estuary has saline water conditions during dry
weather, yet experiences a heavy infl ux of freshwater from San Diego Creek and
other tributaries during major storms. Water quality in the Lower Bay is intermediate
between the Upper Bay and the Pacifi c Ocean.
2.3
Land Use
Land within the Newport Bay Watershed was fi rst settled during the late nineteenth
century, leading to the development of agriculture on a large portion of the inland
areas. The end of World War II brought urbanization to the area, and land use changed
signifi cantly in the past 60 years from agricultural to residential and commercial
uses. In 1983, agricultural and urban uses accounted for 22% and 48% of the Newport
Bay Watershed, respectively, but by 1993, the proportions were 12% and 64%
(US EPA Region IX
1998
). As of 2000, agricultural uses had dropped to approxi-
mately 7% of the watershed area (US EPA Region IX
2002
). Based on plans for
development of agricultural lands, this trend is expected to continue.
2.4
Water Quality
Both Upper and Lower Newport Bay and San Diego Creek have been listed as
impaired for possessing “unknown toxicity.” The toxics TMDL promulgated in 2002
by US EPA Region IX was intended to address the unknown toxicants responsible
and develop limits for selenium, metals, organophosphates and organochlorines.
Other TMDLs are in place for nutrients (US EPA Region IX
1998
), fecal coliforms
(SARWQCB
1999
), and sediment (SARWQCB
1998
).
Researchers have observed acute toxicity in San Diego Creek and Newport Bay.
Acute toxicity was observed in urban storm water runoff and in agricultural drainage
from some types of crops in the watershed (Lee and Taylor
2001
). Bay et al. (
2004
)
collected sediment samples in 2000 and 2001 and found toxicity at multiple locations
in both Upper and Lower Newport Bay. It was concluded in both studies that the acute
toxicity was not caused by organochlorine compounds, but more likely was attribut-
able to organophosphate (diazinon and chlorpyrifos), carbamate, and pyrethroid pes-
ticides (Lee and Taylor
2001
; Bay et al.
2004
). Although uses of diazinon and
chlorpyrifos have been phased out by the US EPA, other organophosphates, carba-
mates and pyrethroid pesticides are still used in residential, agricultural and commercial
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