ML20079N352

Thermal Plume Study

ML20079N352
Person / Time
Site:	Fort Calhoun
Issue date:	09/30/1973
From:	OMAHA PUBLIC POWER DISTRICT
To:
References
RTR-NUREG-1437 AR, NUDOCS 9111110175
Download: ML20079N352 (19)

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p Tr!(?*Cbe w _s f WrtmAL PLR R E G m b'r INIBODUCTION The L crmal Plume Study was conducted at the Fort Calhoun Nuclear Generating Station, Unit No. 1 (FCS) en=mencing in September. 1973. The initial dzte of significant reactor core output and associated thermal discharge vns August 21, 1973. Ce=sercial operation of the station began on September 26, 1973. Tha FCS, which is located about 19 miles nu@ northwest of Omaha, H2branka, at Missouri River Mile (RM) 646.0 (Figures 1 and 2) has a gross output of h81 electrical megawatts. The station is situated on the Nebraska side of Me Missouri River bank.

CooliEg water is drawn into the plant at a ente of 365,000 gallons per minute (gpm). Thedischargefromtheonce-throughet,olingsystem rejects approximately 3.3 x 10 BTU /hr. into the Missouri River.

During normal plant operation, when the river temperature is greater than 55"F, the difference ( AT) between the ambient tempera-ture of the river measured just wtream from the cooling vnter intake structure and the temperatuis of the cool'ng water discharge cannot exceed 20 F. It cannot exceed 30 F when the river temperature is less than or equal to 55 F and rive- flov is greater than 7000 efs. These temperature limits may b .aeeded for brief periods during changes in power levels, and as accessary to maintain facility operation during a grid emerge.ney, to maintain protection of critical plant equipment and systems and for certain safeguard operations which cannot be limited or negated by condenser cooling vater requirements.

These safeguard operations included automatic plant trips and manual trips initiated by licensed personnel during emergencies.

The discharged heated vater rapidly mixes with the turbulent Missouri River creating a thermal plume which hugs the Nebraskt shore-line. It is this heated discharge that has been monitored since commencement of plant operation in 1973 Five years of study, mapping the nature of the thermal plume, have provided conclusive relationships between thermal discharge and Missouri River flow.

Thermal measurements were collected by Omaba Public Power District, the Nebraska State Department of Environmental Control, and Texas Instruments, Inc. The aerial infrared mappings vere conducted by Texas Instruments to determine the nature of the thermal effluent during the vinter months for representative river flow conditions.

All information has been campiled to describe the nature of the thermal discharge resultant from the or e-through cooling water system

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at TCS. ' This discharge 6perates under a thermal maximum NPDES limitation of 105 F. No other thermal effluent limitations for operation presently exist. Neither Title 40 CFR Part 423 or the State of Nebraska Water Quality Criteria impose any restrictions other than the thermal maximum.

Specific objectives of the study weret

1. To determine the physien1 dimensions of the thermal plume.

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SCALE IN FEET 0 1000 2000 3000 4000 5000 6000 Figure ~2: Site area map of Port Calhoun Station on Missouri River near Blair, Nebraska.

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col) determine the nead for further thermal plume data 3.

k. To access the need for a mathematical emal plume model, th To evaluate the effectiver.ess recordings. of aerial i nfrared thermal

!%TERIldS AND METHODS these procedures involwd lowered by a boat-mounted crane. on theplume utilizatiht0 mapping. procedures we One of of a tempe: Iture probe formed during hazardous ice canditions the utilisation of aerial infrared scanniThe other onng.the Missouri River involved procedure Sur see and Triple Deisth Plume s r. Analy i Theprobeofaca.11bratedMontedorogitA t.? TF 200, having an accuracy of f0ney 34

- zed for the surface plume.

2 thermometer boat-mou Kg. lead veight whic. vas rigge_d to a vi vinch was bolted to a U.S.G.G. nch and cablecrane system. mount dP (Table 1 one foot Starcraft Maricer boat. e The face. Tue vinch and crane assembly wasto an eigh used to position established scid (Tables 2 through h) nches below the water sur-the temperature probe six iTempera

. ere recorded on an Distances were marked downstream hae of flags on the Nebraska riv orientated sample points.from thDsta was co Missour' River mile markers banks. er bank and locatedthe Corps on b cf Engineerse plant's d matic distance finder calibrated at distaDistance an Edscorp Field Range Finder calibrat feet. e m ned by using a range-nces ofd19 to 250 yards and the transects. Downstream andere across river distances wat distan designed to produce i i: barge prior to the collection -

of in plAmbient temperature eam of the thermal dis-

! temperature was<then rechecked ume every h temperatures.

The ambient collection procedure and after its completionour during the temperature The data .

form (Tables 2 through h). collected was tabularized and reported o n a standard on each transect until a 0.1 F differe Oftentimes, the 1 nce F above was notwasobtainablend ambient al of 1 F vas obtained.

river obtained, do downstream from the station.

main channel of the Shallov Missouribackwater often causeareas v e adjacent to the du arming trends due to increased i

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a solar radiation. This can influence dovnstream temperatures making it impossible to obtain the i F differential.

Triple-6epth th;:rmal plume data was collected utilizing the same equipment and procedures as utilized for the surface thermal plume me asurements . The triple-depth readings were recorded at the river surface, one-half depth, and at the bottom. A 3h Kg. lead weight, with an attached metered cable system, was lowered into the river bottam to obtain the rivtar bottom te=perature and depth. The bottom depth was multiplied by one-half to obtain the mid-depth sample location. The lead vel.dht was repositionei, and the mid-depth tempera-ture was thet, recorded. The lead weight was again repo-itioned (at approximately 6") to obtc.in the surface temperature. The data was tabularized and reported on standard forms (Tables 5 through 7).

Temperature readings for surface and triple-depth plumes vere completed vitrin a daily eight-hour work period. The temperature data collected consisted of a set of absolute temperatures taken at each grid point based on the in-plume and established ambient temperature data. The AT data was then used as input to a computer program INTER. The program then calculated do.nstream grid point location.s of isotherms of interest, usually 7, 5, 3, 2, and loF (Figure h). The grid point locations were then plotted on scaled graph paper.

Grid poir.t locations for each AT vere then et nnected to produce an isothermal plot. "hese plots were prepared for all surface and triple-depth plumes.

Merial Infrared Scanning Airborne thermal infrared data was collected by Texas Instruments, Inc., Dallas, Texas, by the use of an infrared line scanning system mounted on an airplane. "Nc following procedure is a reduced summary of a much detailed procecurr c dtten by Texas Instruments.

The infrared equipped airplane is desigaed so that one pass over the station vould supply complete coverage' of the river. The airplane's scanner contained two calibrated temperature sources that provided temperature inputs needed to receive the recorded digital temperature data. The thermal infrared data vaa then recorded as a record on ennventional photogrcphic 70 mm film and sintultanecusly vao digitally recorded on magnetic tape. The film record provided a relative grey level d cture ?f the surveyed area, while the 11gital record provided a secot.2 source of que.ntitative te=perature data. The film prcduced a series of straight line river segments, which vere pieced togethat to make a continuous picture of the river.

Correct water temperatures canot be provided directly by even the best calibrated scanner. Atmospheric conditions such as moisture, scan and cloud conditions, carbon dioxide, etc., influeace the true temperature readings of the water. To compensate for these variables,

r9und truth measurements were also taken during tne infrared flight.

Ten.perature readings above the plant discharge, and in the it. mediate -

discharge of the plant, were taken-and then related to the infrared scanning.

When all paraceters were knovn, and the resulting factors com-puted, a computer program was used to produce a map of water tempera-tures by means of a direct printout. The system was also progra==ed to produce a map of temperature differences from ambient conditions.

The computer program prints out a two-digit temperature number every 6k feet of ground distance in the scan direction and every 56 feet along the direction of flight (up and down river). This producer a map scale of one inch equal to 280 fee from a normal h,000 foot overflight. The resulting map is photc. W cally enlarged or reduced to produce the desired map see:.e _e infrared overflight renults in a surface the- si m (Fist i.

RESULTS AND LISCUSSION The thermal plume study began on Septe=ber 17, 1973 Data collec-

, tion was performed monthly, generally during the period of April through November when access to the river was available. Some vinter plumes vere accomplished by boat when safe conditions prevailed. Five infrared flyover mappings were conducted, four of which were flown in the vinter for representative vinter river flow and plant operating conditions. Thermal plume and infrared data collection dates were celected to represent high, lov, and average Missouri River flows.

Data was also ecliected under variable plant operating ; ' cent power and 6T conditions as the opportunities afforded themsel: ..

Figure 3 presents river flows trou September,1973 thmugh December, 1977 The highest river flova vert recorded during 197L For means of comparison, the river flows on the five years were cate drized to represen,, lov, average, and high river flow conditions based upon Figure 3. Low river flows were selected to range from 15,000 through 34,999 cfs; average river flova ranged from 35,000 through.h9,999; and high river flows ranged from 50,000 to 70,000 cfs thrcughout the five-year study.

Unde- the direction of rw.iha Public Power District, thirty-six thermal plumes and five aerial infrared maps were ecmpleted during the five-year study (Table 8). Oross megavatt 1 cad (MW), percent power, Missouri River flow, and 6T for all plumes are also designated on this table. The discharge of heat in BTU /hr. is directly related to the station's operating capacity in terms of percent power. Therefore, percent power was ut'lized throughout this discussion for analysis purposes.

Table 9 associates all plumes conducted under the direction of 0FFD into the three conditions of river flovs. From this table, a

s total of sixteen plumes vere selected to analyze the heat dissipation characterica under similar percent power and river flow conditions.

Tables 10 and 11 vere constructed to analyze the length and vidth of the 7"F, 5 F, h*F, 3 F, 2 F, and 1 F isotherms in terms of distances downstream from the immediate thermal discharge and distances across river from the Nebraska river bank. The'information demenstrated that the-dispersion of heat occurred lenst rapidly under conditions of low river-flov and greatest percent power output by the plant.

These conditions prevailed on three occasions when thermal plumes were measured: December 2,197k, when percent power reached 80% and river flov vas 18,500 cubic feet per second (cts); February 28, 1977, when percent power was 96% and river flow vas 16,800 cfs; and March 16, 1977, when percent power was 96% and river flow was 22.h00 cra.

All of the above three power outputs were above the average 78.h%

power output for all 0FFD surface thermal plumes conductad (Table 8),

and the river flows were below the average five-year rive: flow as can be seen in Figure 3. The isotherms of greatest extent lengthvise were experienced in the lov flow conditions. The lon6etz aurface thermg1 plume was measured on February 28, 1977 On this occasion, the 5 F isotherm extended beyond 5500 feet downstream of the i= mediate thermal discharge (Table 10). Isotherms extending vidth-vise across the river (Table 11) indicated that tbe plumes conducted during low river flows showed, on an average, that the 7"F, 5 F, etd L FD isotherms extended further across from the Nebraska river bank than those plumes conducted during average and high river flow conditions. ,

A plume measured by aerial infrared scanning was conducted on February 6, 1975, at a river flow of 19,000 efs and 77% power (Table 12). The 8 C isotherm disappeared at 83k.h feet downstream of the thermal discharge, and the 7 C isotherm disappeared at 1h87.5 feet downstr eam of the discharge. A review of the surface thermal plume data collected on February 28,D1977 (Table 10),under similar flow conditions, revealed that the 7 F isotherm disappeared at h700 feet downstream of the plant's discharge. The February 28, 1977 si.-

face plume was conducted vnen the plant was operating at 96% power.

A review of the same data in terms of vidth of isotherm across river from the Nebraska river bank revealed that the 8 C and 7 C isotherms reached maximum vidths of 43.8 and 59.h feet respectively, on February 6,1977 (Table 13). The February 28, 1977 surface plume's 7 F isotherm reached a marimum of 63 feet across the Nebraska river bank (Tabie 11). The data demonstrated that the hature of the plume'~

is also influenced by percent power as well as river flow. Fercent power, or beat production, increases the dimensions of the plume.

Missouri River ice flow has been demonstrated to affect the extent of plume isothemal dimensions under conditions of sin 11ar plant power

. production and river flow. Flume data was collected by infrared scanning on December 19, 1975 when ice was present and river flov and plant power were 20,500 ers and 88%, respectively. Data without ice present was

r collected by the same method on January 23, 1976, when river flow vas 26,000 cfs and plant power was 87%. When ice was present, the 5 C isotherm extended approximately 553 feet downstream, as con-trasted with the same isotherms downstream extent of lh69 feet, when i no ice was present. The downstream extent of the 1 C icotherm with ice was three miles; vithout ice present it was six miles. This data indicates that the ice under these plant power and river flow conditions reduced the isothermal dimensions by a factor of at least two. Total plume width in the area of the thermal discharge was >

not discernibly modified.

The most rapid dispersion of the thermal plume was documented under conditions of high river flow. This condition was predominant during the period of July through December,1975 The average river flows for these six months was 63,167 cfs, and the average percent power was 85.3% (Table 10). Under these conditions, the 7 isotherm, on the average, reached a maximum of 29h feet downstream as opposed to an average of 2,657 feet for the same isotherm under lov river flow conditions. The 5 isotherm was about ten times shorter during high flow conditions than lov flow conditions, reaching 413 feet downstream as opposed to kh50 feet when the river flow averaged 19,233 cfs (Table 10).

The marimum vidth t:f the isotherm across river was smaller during high river flow conditions as compared to low river flow conditions.

The average width of the 7 F isotherm was kT feet, and the average width or the 5 F vas 66 feet during high river flows. The average width of the 7 F isotherm during low flow condition was 89 feet, and the average width of the 5 F isotherm was 106 reet (Table 11).

The average river flow conditicas with associated similar percent '

power produced length and width dimensions that correlate with high l and low river flow conditions in that the data lies between the two extremes (Tables 10 and 11).

The Nebraska State Department of Environmental Control (DEC) also conducted surface thermal plume studies at the FCS. During 1973, 197h, and 1975, a total of thirteen plumes were conducted. These plumes vere obtained from an unpublished report of " Environmental Effects of Warm Watar Discharges From Two Nuclear Power Stations on the Missouri R3ver," and' vere categorized into high, low, and .

average flow conditions. The lengths and vidths of these plumes  !

vere determined and presented on Tables lh and 15.

When reviewing the results of both the DEC and OPPD thermal plumes, it becomes readily apparent that the most influential physical river factor governing the dissipation of the thermal offluent is the amount of river flow. Most of the DEC plumes were taken on days favorable for rapid te=perature dissipation (Tables lh and 15). "

Eight of the thirteen plunes were conducted during 1975, the year noted for the highest river flows occurring during the five-year f

study (Figure 3). The DEC plumes were conducted during high river flows that averaged 60,975 cfs, low river flows that averaged 28,100 crs, and average river flows that averaged h3,450 efs.

The averaged percent power for DEC plumes corresponding to high, low, and average river flows are 87 9%, 51.8%, and 73.5%, respectively.

• Due to the above differences in percent power levels, a comparison of plume lengths and vidths in relation to river flow characteristics is difficult. However, the overall characteristics of the DEC surface plumes are similar to 0FFD surface plumes in that the isotherms dissipate in the same general location. Tables ik and 15 reveal that the isothem lengths and vidths diminish in order of largest isothea a to smallest isotherm (5 C, h C, 3 C, 2 C, and 1 C). This same pattern is generally found on OPPD surface plumes. General configurations of the DEC's surface plumes (Figure 8) are quite similar to those plume measurements taken by OPPD (Figure 5).

Triple-depth thermal *1ume data was dso collected. Temperatures were taken at three depths: the surface, one-half depth, and the I

bottom. A typical triple-depth plume represented on Figure 6 shows the heat dissipation at the various depths during average river flow conditions. . This triple-depth plume condueced on April 15, 1976, at a Missouri River flow of 35,000 efs, indicates the configuration of the three plumes. Tables 16, 17, and 18 vere presented to compare triple-depth plumes under high, low, and average Missouri River flow conditions. Transect No. 1 is the ambient or unaffected sample location. Transect No. 1.5 in the most influenced location. On all three Tables 16,17, and 18, the largest AT's are recorded at transect No. 1.5. Higher t.T's are present at the 1.5 location as compared to locations further downstream from the FCS's thermal discharge under all river flow conditions. During low river flow conditions (Table

17) the AT's are higher at all locatio-' than the AT's occurring during high and average river flow conaltiuns, but the pattern of vertical strat'fication remains similar to the vertical stratification occurring during high and average river flow conditions. Essentially, complete vertical mixing occurred at transects ~ 2 through 5 or distances greater than 2,000 fr.et downstream frem the discharge for hil triple-depth plumes regardless of river flow conditicus.

During the course of the plume studies, dat. has been collected for river flows ranging between 14,000 and 67,000 cfs. Plumes falling within this range of flow have been shown to exhibit isotherm lengths -

and vidths falling within these extremes. It has also been shown from the triple-depth data that complete vertical mixing has occurred approximately 2,000 feet downstream of the plant discharge. The Fort Calhoun plume configuration has nov been identified under the plant operating and river flow conditions experienced since the unit began to operate.

The Fort Calhoun Station is not currently operating under any limits or constraints with respect to thermal plume dimensions. The current State of Nebraska Water Quality Standards exe=pt effluents from these requirements. Also, as specified in the Code of Federal Regulations l l

x m (40 CFR Part 423), units smaller than 500 !N, or in service before January 1,199 s did not have a theru l effluent limitation. Fort Calhoun's themal discharge to the Misbouri River operates on National Pollutant Discharge Eliminaticn System Pemit No. NE 0000418 and has as its only temperature requirement a thermal maximum.

Due to the fact that there are no current thermal plume regu-lations and that five years of monitoring has produced plume data for all comonly occurring plant power and river conditions, it is believed by the District that themal plume monitoring should be dis-continued. The District has utilized this same line of reasoning for not pursuing at this time the development of a methmatical thermal plume model as specified in Technical Specification 2.1.2 of Appendix B to Operating License DFR h0. It is believed that there is no justification for expenditures in model development. Based on the current regulations, the District vill not be in a position to put such a model to any practical utilization.

SUINARY AND CONCLUSIONS Five years of studying the nature of the themal plume indicates that the magnitude of the thermal plume dimensions is dependent primarily upon percent power (total BTU's of heat discharged) and upon Missouri River flow.

Under all conditions tested to date, a zone of passage for the movement or drift of fish and aquatic biota has been maintained.

Aerial infrared data was valuable in that it made possible the collection of vinter data, under hazardous river conditions.

Triple depth data documented that under most river flow and plant power conditions, complete vertical mixing of isothems occurred by 2000 feet downstream of the plant discharge (transect 2).

The Fort Calhoun Unit 1 thermal effluent hugs the shoreline when discharged, and rapidly dissipates as it is mixed with ambient temperatre Missouri River water. The 5 F isotherms is commonly dissipated by 2000 feet downstream of the discharge.

The District-produced surface plumes, the infrared scanning-pro-duced plumes, and DEC-produced plumes compared favorably with respect to plume dimensions.

Floating ice reduced thermal plume dimensions by approximately one-half, with river flows of approximately 20,000 to 26,000 cfs and

-percent power of 87 to 887.

Sufficient thermal plume data has been generated to demonstrate plume configuration under co=nonly occurring plant operating and river flow conditions and justify the discontinuance of the thermal plume monitoring program.

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A mathematical-thermal plum medel would not be able to produce information utilizable by the District that has not already been pro-duced-oy plume mapping. No regulatory requirements, either Federal or State, are applicable to the Fort Calhoun Station Unit 1 thermal plume, making a justification for a plume model questionable.

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1 Chapter 2 FISH IMPINGDENT STUDY By Ronald G. King Technical Specification 2.2 t

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1. Introduction Fish impingement studies at Fort Calhoun Station have been concucted from Mcy 1973.through December 1977. The studies were initiated to collect dats n2cessary to evaluate the effects of impingement losses on the Missouri River fith connunity near the Station. The number, size, species, and physical condition of fish impinged on the traveling screens were determined. Daily camples were collected at noon (12 hr) and midnight (!2 hr) from May through S:ptember and at noon only from October through April. A total of 2345 hourly camples was collected during the 56-month st6dy. In addition, 24-hr impingement studies were conducted on 29 occasions from 1974 through 1976 to determine diurnal impingement rates. Impingement rates from the daily and 24-hr studies were cycluated to determine the best estimate of impingement rates at Fort Calhoun Section.

II. Methods Fish were removed manually f rom the traveling screens f or 60 min following clecning of the screens. During each hourly sampling period, one of the six ,

trcveling screens was sampled on a rotational basis. All six screens were campled during the 24-hr studiec. Omaha Public Power District personnel collected the samples and compiled the data for the daily studies and the 1976 24-hr studies. The Ecosciences Division of Henningson, Durham & Richardson con-ducted the 24-hr studies in 1974 and 1975 (Henningson, Durham, & Richardson 1976).

III. Description of the Cooling Water Intake Structure The Fort Calhoun Station Antake is a reinf orced concrete structure extending cpproximately 80 ft along the river bank at River Mile 645.85. Water is drawn into the intake by three 120,000 gpm capacity circulating water pumps. Water passes through a vertical trash rack with 3 inch openings prior to entering the six forebays. Water entering the plant must pass through the sluies gate openings located at the base of a curtain wall. Trash and dcbris which pass through the trash rack are removed by six traveling screens made of steel mesh with 3/8 inch equare openings. A high pressure (110 psi) screen wash system is used to clean tha screens. The screen wash trough discharges Lato the river at the downstream eide of the intake structure.

IV. Results and Discussion A. Species romposition A total of 45 species was collected from the traveling screens at Fort Calhoun Station (Table 2.1). Species commonly impinged, in decreasing order of occurrence, included freshwater drum (29.5%), gizzard shad (21.0%), channel cettish (9.0%), black bullhead (6.5%), uhite bass (6.2%), white crappie (4.4%),

and bluegill (3.6%). Combined, these species comprised 74 to 88% of the annual impingement and made up _80% of the fish sampled during the _56-month study.

Freshwater drum and gizzard shsd were the most common species impinged throughout the study except in 1976 when channel catfish were the second most common fish collec' d (Table 2.1). Species that vere occasionally common in the impingement collectisas (comprised more than 1% of the impinged fish) included carp, river 30

catpsucker, stonecat, flathead catfish, green sunfish, yellow perch, and sauger.

Game fish (excluding freshwater drum) comprised from 25 to 62% of the annual impingement at the Station and averaged approximately 39% over the entire study.

No rare and endangered species (Nebraska Game and Farks Commission 1977) were 12 pinged. Several species that were infrequently impinged,_ including mooneye, blacknose dace, highfin carpsucker, and black buffalo, are listed as uncommon native fishes in Nebraska (Morris et al.1972) and as threatened species by Miller (1972). "The silver jaw minnow was impinged in 1973; however, it apparently is not a native Nebraska fish (Morris et al.1972) and according to Cross (1967) probably does not occur natural 3y west of the Mississippi River.

B. Sire of Irminged Fish Fish impinged on the traveling screens et Fort Calhoun Station were generally less than 100 mm in length. During the 56-month study approximately 70% of the fish sampled were 100 mm or less. Fish longer than 100 mm were impinged primarily f rom January through J me. Nearly half of these larger fish were collected from November 1975 through May 1976. Based on published length data (Carlander 1969, 1977), few adult fish were-impinged. Fish larger than 199 mm comprised only 2.7% of the fish sampled. Freshwater drum, shottnose gar, and gizzard shad accounted f or approximately 60% of the fish that exceeded 199 mm in length. The small openings (3 inch) between the trash rack bars, the greater swimming ability of larger fish, and distribution of adult fish were the principal reasons why fewer adult fish were impinged at Fort Calhoun Station. Electroshocking catch data collected near the Station indicated that fewer adult fish utilized the cutting bank habitat along the Nebraska shore when compared to the quiet water habitat behind the wing dikes along the lowc shore (Chapter 1). Adult individuals of small species, such as stonecat, centrachids, and black bul'lheads were commonly impinged.

The average length of impinged fish decreased in July (Figure 2.1) when young-of-the-year (YOY) fishes were large enough to be retained on the screens. Approximately 90% of the fish impinged between July and December were YOY fish that were 100 mm or less in length. The lengths of impinged fish were variable throughout the study; however, the monthly or annual average length of impinged fish seldom exceeded 140 mm (Figure 2.1). The average length execeded 140 mm only when fewer .than 10 individuals of each of the three most common species '(freshwater drum, gizzard shad, and channel catfish) were sampled in a given month.

C. Physical Condition of Impinged Fish Fish sampled from the traveling screens were classified as either alive or dead. The physical condition of impinged fish was variable ranging from C to 90% dead on a monthly basis (Figure 2.2) . Survival was lowest when water remperatures were high (July through August) or when most of the fish-impinged were gizzard shad or freshwater drum. The highest survival occurred at low water temperatures or when most of the impinged fish were ictalurids.

The percentage of dead fish generally increased in July and remained high into early winter. During this period YOY fishes dominated the samples and l.

the average length of impinged fish decreased (Figure 2.1). Only 25% of fish larger than 199 mm were recorded as dead, while 60% of the fish larger than 299 mm were dead. Larger fish may have been stressed prior to being entrapped 31

in the forebay area. The length of time that fish are entrapped in the intake structure before being impinged is an important factor in determining the physical condition of fish sampled f rom the screens. The physical condition of fish in the intake may progressively deteriorate with time.

Approximately 50% of the fish sampled were recorded as dead during the study. The annual percentage classified as dead ranged from 30.7% in 1976 to 73.4% in 1974. Similar trends among years were also noted at Cooper Nuclear Station, approximately 113 miles downstream of Fort Calhoun Station (King 1978).

The low percentage of dead fish in 1976 was attributed to a reduction in >

number of gizzard shad and freshwater drum in the impingement collections and ,

a higher survival of these species. During all other years 95% of the dead fish were gizzard shad and freshwater drum, compared to-27% in 1976. Of the

• major species impinged (Table 2.2), gizzard shad had the lowest percent of individuals classified as alive (28.3%), followed by freshwater drum (38.2%),

bluegill (50.6%), white bass (51.3%), white crappie (53.6%), channel catfish (71.8%), and black bullhead (80.9%). The survival rate of impinged fish classified as alive af ter being returned to the river is not known. Therefore, because of the varying degrees ci physical damage reported by Henningson,

• Durham and Richardson (1976) and the high pressure screen wash, 100% of the '

impinged fish were assumed lost from the fish community.

D. Impingement Rates Daily impingement rates (no. fish /hr per screen) were highly variable. -

ranging from 0 to 71 fish /hr per screen (Figure 2.3). No fish were impinged j during approximately 57% of the daily sampling periods. Impingement rates .

were generally less than 10 fish /hr per screen with higher rates recorded on '

only 68 dates during the 56-month study (Figure 2.3). High impingement rates

(>10 fish /hr per screen) were generally associated with imptagement of fresh- '

water drum and gizzard shad. Cizzard shad comprised all but three of the fish sampled on 13 July 1975, when the highest impingement rate was recorded (71 fish /hr per screen). Other species that dominated the samples when impingement rates exceeded 10 fish /hr per screen included channel catfish, black bullhead, white bass, green sunfish, and white crappie.

Year-to-year variability in impingement rates .was attr1buted to .

several factors. Eigh impingement rates in the winter are related to reduced swicming ability of fish in cold water and the higher approach velocities at the intake structure associated with reduced river flows. Fish . activity '

also may increase as the river flow decreases since fish must seek wintering arets as the backwater areas are dewatered. Although there appears to be a general relationship between impingement rates and river flow, it was not always evident. For example, the lowest approach velocities occurred in 1975 during the high summer flows (Figure 2.4), yet the lowest summer impingement rates occurred in 1976 when river flows were substantially lower. Impingement rates are probably related more to fish movements and abundance of YOY fish than' strictly to flow conditions.

The highest impingement rates occurred f rom December 1975 through May 1976. The impingement rate rema1ned high during this period; however, in other years the rates decreased in the winter and early spring (Figure 2.3).

Fish collectcd f rom the traveling screens f rom December 1975 through May 1976 32

accounted for approximately 30% of the fish sampled during the entire study, and the number sampled was 5-9 times greater than during other comparable periods.

Impingement rates increased significantly on 4 December 1975 (Figure E.3) following

~

a rapid decrease in_ river discharge (Figure 2.4). Reduced flows probably caused fish to disperse from the previously inundated shoreline and backwater areas.

Based on size data, these high' impingement rates indicate a greater abundance of YOY and yearling fish in 1975-76 than in other years. The high river flows from July through November 1975 may have created larger nursery areas for YOY fish which may have resulted in the increase in YOY fish. Increased recruitment of YOY fish may also have resulted from the high discharges from Lewis and Clark Lake, since Walburg (1971) reported that large numbers of YiOY fishes are discharged through Javins Point Dat.

Size is also an important factor contributing to variability in im-pingement rates. The highest impingement rate occurred on 13 July 1975 when the everage length of impinged fish vas less than 60 mm. Impingement rates generally

. decreased when the average size of the impinged fish increased. Swimming speeds of-fish are directly related to body size and water temperature (Bainbridge 1958). At the water temperatures reported at Fort Calhoun Station the sustained swimming speeds of most smaller fish are slower than the apprcach velocities through the sluice gates (Henningson, Durham and Richardson 1976).

It is apparent that several interrelated factors affect impingement rates at Fort Calhoun Station. Natural variability in water temperature, epawning and recruitment success, seasonal distribution and abundance of fishes, cnd controlled river' flows all apparently affect impingement at Fort Calhoun Station.

impingement rates at Fort Calhonn Station exhibited diel dif f erences

.(Figure. 2.5) based on the 22 24-hr studies conducted in 1974 and 1975 (Henningson, Durham and Richardson 1976). Impingement rates at night (2000 to 2200, and 0200 to 0400 hr) were significantly Ip < 0.05) higher than during midday (1400 to 1600 hr). Seven additional 24-hr studies during 1976 indicated a similar trend (Figure 2.5). The number of fish impinged during the summer months ~1n 1976 (<50/24-hr) vas too low to establish diel differences. The daily e mples collected hourly at noon and midnight generally did not exhibit these differences (Table 2.3). The lack'of.diel dif.ferences in the hourly studies wts probably related to the scheduled sampling periods. The impingement rates st_ Cooper Nuclear Station, where samples vere collected at random times, were i generally higher at night (King:1978). .There were no apparent diel differences i in the impingement rates of the major species (Table 2.5).

Diel differences in impingement rates have been attributed to increased i fish activity from early evening throu3h the morning hours, decreased visibility of .the traveling screens at night and the physical condition of impingad fish (Landry and Strawn 1974; liyman et al.1975; Marcy 1975) . Landry and Strawn (1974) reported increased catch rates at night when poor visibility of the traveling screens probsbly decreased screen avoidance, while during daylight hours, injury rates were high, suggesting that fish in a weakened condition could not avoid the screens. Large differences betwnen day and night in the percentage of alive impinged fish at Fort Calhoun Station occurred in 1975 (Iable 2.4). In 1975, 24% of the fish sampled during the day were alive 33 m-

l compared to 46* at night. These differences, however, did not result in dif f erent impingement rates when day and night'sauples were compared (Table 2.3) .

Data from the 24-hr and hourly impingement studies were compared to determine the reliability of using daily impingement rates to project the total number of fish impinged at Fort Calhoun Station. Hourly samples overestimated daily impingement rates on 14 of 29 occasions and underestimated daily impinge-ment rates on 12 dates when comparable 24-hr data were available (Table 2.5).

High impingement rates, which occurred over a few days, were frequently missed by the 24-hr studies which were conducted monthly or biweekly. For example, the high 1spingement rates which occurred over a 6-day period in July 1975 (Figure 2.3) were not detected by the 24-hr studies conducted on 5-9 and 22-23 July 1975 (Table 2.5). The daily samples were most likely to underestimate impingement rates when fish appeared sporadically on the screens (Figure 2.3).

Despite these differences, the daily impingement values based on the number of fish /hr per screen were not significantly (p > 0.05) dif ferent from the 24-hr studies when compared using the paired "t" statistic (t = 1.56, d.f. = 28). The impingement rates for each of the six screens were compared to determine if a certain screen or screens biased the monthly impingement rates. Even though .

considerable variation in impingement rates occurred among screens (Table 2.7),

no statistical differences (p > 0.05) were evident. The 24-hr studies also indicated that the differences in impinSement rates among screens were not significant (Hanningson, Durham & Richardson 1976). Based on these comparisons, the daily samples provide an accurate estimate of the monthly impingement rates.

Projected monthly impingement ranged from 288 fish in February 1975 to 42768 fish in March 1*76 (Table 2.8). An estimated 492,040 fish were impinged at Fort Calhoun Station from May 1973 through December 1977.

E. Impact Commercial catch data from the Missouri River between Sioux City, Iowa, and _ the Platte River indicate no decline in the fishery following Station start-up in 1973 (Table 2.9) . The c-rch per piece of fishing gear increased from 3.8 fish in 1974 to 6.8 and 6.1 tish in 1975 and 1976, respectively. The catch of carp, buff alo, and suckers has increased from 1974 through 1976, whereas the catch of channel catfish has declined since 1974 (Table 2.9). The catch per piece of fishing gear f or channel catfish decreased f rom 1.5 in 1974 and 1975 to 1.0 fish in 1976.

The impact of the removal of nearly 500,000 fish from the Missouri River can be put into perspective by comparing the number impinged with available harvest data. Commercial catch data f rom the Missouri River were compared to the number of important commercial species impinged at Fort Calhoun Station (Table 2.9). Because most of the fish impinged were YOY or yearling fish, all of these fish would not have survived to harvestable size. Hesse and Wallace (1976) determined the annual mortality rates for five commercial species in the Missouri River. Using these data, the number of impinged fish that may have re 'ched harvestable size, had they not been impinged, can be estimated (Table 2.9) .

These estimates are conservative since mortality rates of age class 0 fish were

.. not determined, except for bigmouth buffalo. The potential number of harvestable fish remo'ved by impingemeat was low, except in 1976 when a high number of channel 34

catfish was impinged (Table 2.9). Since commercial species in the Missouri River are generally 3-4 years old befcre they reach a harvestable size (Hesse and Wallace 1976; Schainost 1976), the impact of impingement losses would not affect the commercial catch until 1976 and 1977. The 1977 commercial catch data are unavailable at this time. The decreased catch of channel catfish in 1976 was probably related to factors other than impingtment, since the impingement rates of channel catfish were low in 1973 and 1974. Schainost (1976) suggested that the general decline in the Miesouri River commercial fishery may be due to a change in the type of fisherman. Evidently commercial fishing on the Missouri River is becoming more of a hobby than a livelihood.

Mortality rates of the two most common species impinged (gizzard shad and freshwater drum) have not been determined in the Missouri River.

Survival of gizzard shad from egg to adult is probably less than 1% based on '

the high mortality reported for other clupeids (Kissil 1974; Leggett 1977).

Assuming a survival rate of 0.1 to 1.0%, approximately 104-1050 of the gizzard shad impinged would have survived to maturity. Comparative data for freshwater drum are unavailable, but assuming a natural mortality of 90%, an estimated 14515 freshwater drum would have survived to maturity. 1 A comparison of catch and relative abundance data f rom 1972-73 surveys in the enannelized Missouri River (Gould and Schmulbach 1973; Stucky 1972) witn (sta collected since 1973 near Fort Calhoun Station and Coop er Nuclear Station (Hesse and Wallace 1976; Bliss 1978a) and near the Nebraska City Power Station i

(Bliss 1978b) indicates no significant changes in the fish populations in the Missouri River.

Losses of fish due to impingement on the traveling screens has had no detectable effect on fish populations in the vicinity of Fort Calhoun Station.

Standing crop estimates necessary to make a direct assessment of impact are not available. However, based on catch and size data, changes in the fish co=munity have not been noted (Chapter 1). The numerical catch near the Station varied substantially among years but species relative abundance was similar from 1973 through 1977. The differene.s in numbers of fish collected were related to an attraction or avoidance of fish to the warm water and subsequent alteration of their distribution. In addition, river conditions caused variations in catch rates, espec1 ally in 1975, when unusually high flows occurred. The average size of fish was quite uniform among years, indicating fish stocks have not been reduced.

Fish losses attributed to impingement may be offset by the natural ,

compensatory capacity of fish pegulations which tends to cause a decrease in death rate or increase in birt' 1 ate as population density declines (McFadden 1977). Since the fish impinge p Fort Calhoun Station are small, immature fish, t

the potential impact on the fish populations in the Missouri River is probably low. If these fish are removed when natural mortality is still compensatory, the removal may be of fset by increased survival and/or growth (Ricker 1954) .

V. Summary and Conclucions

1. Species commonly impinged included freshwater drum, gizzard shad, channel catfish, black bullhead, white bass, white crappie, and bluegill.

Co=bined, these species comprised 14 to 88% of the annual total of impinged fish at Fort Calhoun Station.

35

o

-2. No rare or endangered species were impinged.

3. During the 56-month study approximately 70% of the fish saripled were 100 mm or less~in length. Fish longer than 199 m comprised only 2 7% of the fish sampled.

4. Approximately-50% of the fish sampled were recorded as dead during the stuiy. Survival was related to water temperatures and the size and species of fish ampinged. The number of dead fish was highest when YOY gizzard shad cnd freshwater drum were abundant.

5. Daily impingement rates ranged from 0 to 71 fish /hr per screen. High impingement rates were generally associated with impingement of gizzard shad end freshvater drum.

6. Variations in imoingement rates elated to natural variability in water temperature, spawndar s a recruitu - 4.uccess, seasonal distribution and abundance of fishea, and controlled rivet ' lows.

7. A. comparison of hourly and 24-hr studies indicated that the daily studies provided an accurate estimate of tha monthly impingement rates.

8. Projected monthly impingement ranged from 288 to 42768 fish; an astimated 492,040 fish were impinged at Fort Calhoun Station from May 1973 through December 1977.

9. Impingement losses were assumed to be 100%, although some survival may have occurred since approximately 50% of the fish sampled were classified as alive and were returned to the river. ,

10. A comparison of catch and size data since Station start-up indicates that impingement losses has had little irpact of the Missouri Rfver fish comunity in the vicinity of the Station. ,

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