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Water Quality

Reservoirs (Corps 1999)

Long-term monitoring stations along the Lower Snake River have been used by a number of state and federal agencies going back as far as 1975 (Table 11and Table 12). The sampling locations, frequency, and number of years sampled varies between the various agencies. Much of this monitoring focused on a few key parameters including temperature, pH, conductivity, turbidity, dissolved oxygen, and total dissolved gas supersaturation (TDG). The Corps monitored these parameters, as well as Secchi transparency within each of the reservoirs at a limited frequency of one to four times a year. Occasionally, other parameters such as hardness, total suspended solids (TSS), turbidity, and nutrient levels were measured. The U.S. Environmental Protection Agency (EPA) and the individual states conducted ambient water quality monitoring programs to primarily assess compliance status and trends. The Washington Department of Ecology (WDOE) sampled intensively (i.e., up to 10 samples per year) in 1975 for these same parameters plus fecal coliform bacteria. The USGS samples about once a year at two long-term monitoring stations on the Lower Snake River (Anatone (RM 167) and Burbank (RM 2.2), Washington). The Universities of Washington and Idaho analyzed pre-impoundment water quality at the Lower Granite Dam area from 1970-1972 (Falter et al., 1973). Limited data have been collected, however, on concentrations of various toxins including heavy metals, pesticides, and other organic compounds.
Table 11. Summary of long-term water quality monitoring data for various sampling locations throughout the project area (Corps 1999).

River/Location

River
Mile


Agency

Sampling
Period


No.
of
Years


Sampling
Frequency


Parameters¹

Snake River

Burbank, WA

2.2
8.7

USGS

1960-69, 72-78;
1979-1990

16

1/yr

Conventional parameters

Ice Harbor Dam, Tailwater

6.0

Corps

1991-pres

9+

Apr-Sep (Cont)

B, TDG, Temp, DO

Ice Harbor Dam, Forebay

9.7

Corps

1984-pres

15+

Apr-Sep (Cont)

B, TDG, Temp, DO

Ice Harbor Pool

18

Corps
EPA
WDOE

1975-90
1975
1975-90

9
1
15

3/yr
5/yr
6-10/yr

Conventional parameters except TSS & TN
Conventional par except TSS, Turb, Hardness
Conventional parameters except nutrients

Lower Monumental Dam, Tailwater

40.6

Corps

1991-pres

9+

Apr-Sep (Cont)

B, TDG, Temp, DO

Lower Monumental Dam, Forebay

41.6

Corps

1984-pres

15+

Apr-Sep (Cont)

B, TDG, Temp, DO

Lower Monumental Pool

44

Corps
EPA

1975

1

5/yr

Temp, Cond, DO, pH, Turb

Little Goose Dam, Tailwater

69.5

Corps

1978-1992

9+

Apr-Sep (Cont)

B, TDG, Temp, DO

Little Goose Dam, Forebay

70.3

Corps

1984-pres

15+

Apr-Sep (Cont)

B, TDG, Temp, DO

Little Goose Pool

83

Corps
EPA

1984-pres
1975

9
1

1/yr
5/yr

Temp, Cond, DO, pH, Turb

Lower Granite Dam, Tailwater

106.7

Corps

1991-pres

9+

Apr-Sep (Cont)

B, TDG, Temp, DO

Lower Granite Dam, Forebay

107.5

Corps

1984-pres

15+

Apr-Sep (Cont)

B, TDG, Temp, DO

Lower Granite, Lower Pool

106.5

Corps
USGS
EPA

1978-89
1975-78
1975-77

9
4
4

1-2/yr
1/yr
up to 25/yr

Conventional parameters
Temp & Cond mostly
Temp, DO, Cond, Turb, pH, TP, & OP

Lower Granite, Upper Pool

120

Corps
USGS

1978-92
1974-77

9
3

1-2/yr
1/yr

Temp, Cond
Conventional parameters except TSS, TP, & OP

Anatone, WA

167

USGS
Corps

1974-pres
1999

20+
1

1/yr
Apr-Sep (Cont)

Temp & Cond; other par less frequently
B, TDG, Temp, DO

¹Conventional parameters consist of temperature (Temp.), conductivity (Cond.), dissolved oxygen (DO), pH, total suspended solids (TSS), turbidity (Turb.), total nitrogen (TN), nitrate and nitrite (NO2 and NO3), and total phosphorus (TP). Other parameters include total dissolved gas, measured continuously (TDG), and barometric pressure (B).

Table 12. Sampling stations in the Lower Snake River in 1997 (Corps 1999).



Station
Name


River
Mile


Reach

Reach Type

Purpose




Snake

SNR-148

-148

Asotin

Free-flowing

PP/Limno/ABA

Free-flowing Snake River, little controlled

SNR-140

-140

Lewiston/Clarkston

Free-flowing

Limno

Free-flowing Snake River used in previous studies. Analogous benefits at the Clearwater 1 station.

SNR-129

-129

Lower Granite Reservoir

Transition zone

Limno

Visited in previous studies, and represents the transition between riverine and lacustrine environments.

SNR-118

-118

Lower Granite Reservoir

Reservoir

PP/Limno/ABA

Represents the location in Lower Granite pool where complete mixing of the inflowing Snake and Clearwater Rivers has occurred. Previously visited and part of the primary productivity study.

SNR-108

-108

Above Lower Granite Dam

Reservoir

Limno

Site close to the forebay that was included in previous studies and located at deepest part of the reservoir.

SNR-106
SNR-105

-106/-105

Below Lower Granite Dam

Free-flowing/reservoir mix

PP/Limno/ABA

hybrid of free-flowing/reservoir, but more riverine.

SNR-83

-83/81

Little Goose Reservoir

Reservoir

PP/Limno/ABA

Only station that has consistently been sampled in Little Goose reservoir, and was included in the primary productivity study.

SNR-66

-68/67

Below Little Goose Dam

Free-flowing/reservoir mix

PP/Limno/ABA

Hybrid of free-flowing/reservoir, but more riverine.

SNR-50

-52/50

Lower Monumental Reservoir

Reservoir

PP/Limno/ABA

Snake River impoundment.

SNR-40

-40/37

Below Lower Monumental Dam

Free-flowing/reservoir mix

PP/Limno/ABA

Hybrid of free-flowing/reservoir, but more riverine.

SNR-18

-18

Ice Harbor Reservoir

Reservoir

PP/Limno/ABA

The only site that has routinely been sampled in the Ice Harbor reservoir.

SNR-6

-6

Below Ice Harbor Dam

Free-flowing/reservoir mix

PP/Limno/ABA

Hybrid of free-flowing/reservoir, but more riverine.

PP=Primary Productivity Sampling
LIMNO=Limnological Sampling
ABA=Attached Benthic Algae Sampling

In 1994, the Corps initiated an extensive sampling program throughout the Lower Snake River Basin with the assistance of research teams from Washington State University (WSU), National Marine Fisheries Service (NMFS), and the University of Idaho (UI). The primary goal of this sampling program was to provide a more complete synopsis of the existing limnological and biological productivity conditions above, below, and throughout the Lower Snake River reach and to assess the effects, if any, that the various dams have on water quality. Sampling was conducted both in the impoundments and in the "free-flowing" reaches and major tributaries. Initially, in 1994 and 1995, data were collected on a monthly or bi-weekly basis within the Lower Snake River system. The sampling frequency was increased in 1997 to bi-weekly monitoring through the growing season in the Lower Snake River. An extensive suite of parameters was sampled during these investigations, including many of the same conventional parameters used in the long-term monitoring studies such as pH, alkalinity, conductivity, dissolved oxygen, nutrients, TSS, and turbidity. Various anions and cations were also monitored including chloride, silica, sulfate, calcium, magnesium, sodium, and potassium. In addition, biochemical oxygen demand and sediment oxygen demand were also measured at selected locations as well as various biological parameters including chlorophyll a, phytoplankton, zooplankton, attached benthic algae, and other primary productivity indicators.


As many as 13 sampling stations were established along the mainstem of the Lower Snake River. Upstream and downstream stations bracketed each of the four dams accounting for eight stations. Other key sampling stations include those representing the major tributary inputs to the Lower Snake River, as well as two additional stations in the upper portions of the Lower Granite Reservoir at RMs 118 and 129.
Sediment samples were collected along transects established across the reach of the Lower Snake River and upstream of each dam. Three additional transects were sampled in the McNary Reservoir for a total of 54 transects. Sampling during Phase 1 focused on identifying those locations within the study reaches where the river bed sediment consisted primarily of very fine sand (0.062-0.125 mm) and silt/clay-size (<0.062 mm) particles (CH2M Hill 1998). These locations were to be revisited during Phase 2 for the collection of sediment samples for the analysis of inorganic and organic chemical constituents. Only those areas where fine-grained sediments are present were of interest because it is assumed that only the fine-grained sediments will be eroded and transported by the free-flowing water if the drawdown alternative is implemented, and any organic or inorganic contaminants of concern would be most likely concentrated in the finer-grain-size fraction due to their physio-chemical properties.
Phase 2 of the study involved collection of sediment core samples from the areas identified in Phase 1 as having the highest percentage of fine particles. At each of the sediment sampling locations, river water samples were also collected. The river water samples were collected to perform elutriate tests and to determine existing water quality conditions.
The sediment samples were analyzed for a variety of parameters including metals, semivolatiles, herbicides, pesticides, organics, mercury, and nutrients. Elutriates were prepared for pH 4, ambient pH, pH 10 and for an exotic condition. The exotic elutriation was prepared having a pH of 2.6 and an oxidation-reduction potential (ORP) of 1,100 millivolts. Only the results of the ambient pH were used for the sediment evaluation.
Monthly average flows ranged from a high of about 170 kcfs in May to a low of approximately 25 kcfs in November and December. Flows in August and September of 1997 were nearly twice as high as the historical average flows of 20 to 25 kcfs for these months. In 1995, the mean monthly flows were very close to the historical monthly averages for the first half of the year, and reflect slightly wetter conditions during the summer and fall months. In 1994, average monthly flow levels were consistently below the historical averages with a high of about 75 kcfs during May, and a low of around 10 kcfs for much of August and September. The August and September flow levels were nearly 50% lower than historical averages for these months. The average flow data for 1975 through 1977 contained two years that had above-average flows (1975 and 1976), and one year (1977), which was primarily below average. Although the flow rates at the Ice Harbor Dam varied from Lower Granite Dam, the same seasonal flow pattern and annual variability.

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