“FISHWAYS AT BONNEVILLE DAM”
WAR DEPARTMENT
CORPS OF ENGINEERS U S ARMY OFFICE, DISTRICT ENGINEER
BONNEVILLE, OREGON 1939
Courtesy of the Franklin Delano Roosevelt Library
Foreword
This pamphlet has describing the fishways at the Bonneville Dam has been prepared to furnish answers to many questions asked by visitors at the Dam. Many of the Thousands of sightseers who inspect the fishways are unable to confirm or enlarge their understanding of fish habits and the operating technique of the Bonneville facilities, due to the relatively few guides available. Appropriations for operating the project do not provide funds for guide service, and although visitors are welcomed, the means for disseminating information to them are necessarily limited.
This pamphlet covers those features of the fishways in which experience has shown the public to be mostly interested.
Introduction
Construction of the Bonneville Dam created an unprecedented problem for the passage of fish. Never before had it been necessary to construct fishways at the dam on so large a river, or to provide for such a tremendous annual fish migration. Upon the success of these fishways depended the future of a $10,000,000 industry, which is the estimated annual retail value of the products of Columbia River fishing.
In order that this great natural resource might be preserved, the Army Engineers, in whose hands construction of the dam was placed, collaborated freely on questions of fishway design with the U.S. Bureau of Fisheries and the Fish and Game Commissions of the states of Oregon and Washington. The elaborate structures which accordingly have been constructed at a cost in excess of $6,500,000 have passed adequately all runs of fish arriving at the Dam.
During the first season of operation, the counting stations have checked through the fishways approximately a million fish, of which 470,000 were salmon or trout.
Life History of Fish
Of the many species of migratory fish that use the Bonneville fishways enroute to their spawning grounds in the headwaters of the Columbia and tributaries, salmon and trout are the most important. These include Chinook, Blueback, Silver and Chum Salmon, and Steelhead Trout. Sea run Cutthroat Trout are also found in relatively small numbers. All these fish spend the greater part of their lives in the ocean, entering fresh water only for the purpose of spawning.
The female deposits her eggs in the gravel of the stream beds. About two months later the tiny fish (fry) break out of the egg, but remain in the gravel, drawing nourishment from the yolk of the egg which remains attached to them. As this source of food becomes exhausted, the fish, now known as fingerling, work their way to the surface of the gravel, to start their long pilgrimage to the sea, some rapidly, others leisurely, perhaps remaining for months in the fresh water, depending upon the characteristics of the species.
Growth in fresh water is slow, but is accelerated immediately upon the fingerling�s reaching salt water. The fish increases rapidly in size and begins the storage in its body of large quantities of fat to be used as reserve energy in making the long migration to its spawning ground during which time it takes no food. The salmon become wanderers of the sea for from two to five years, until sexual maturity approaches and they return to fresh water to spawn. Guided by inimitable instincts, they find with remarkable accuracy their way back to the river system of their origin, and even the very tributary in which they were hatched. Those having the greatest distance to travel start earliest, each species having its peculiar characteristics. Spawning is, however, confined mainly to August, September and October.
The true Pacific Salmon invariably die after spawning. The Steelhead Trout may live to find their way back to the Pacific and return to spawn a second or even a third time. Chinook Salmon in the Columbia River Spawn at ages ranging from two to six years; Blueback spawn in their third and fourth year; Silver Salmon in their third year.
The Atlantic Shad was transplanted in the Pacific Coast many years ago and has become quite abundant in many streams, including the Columbia. This species spawns mainly in the quieter water below Bonneville, but a few normally have migrated above that point.
Another commercially valuable fish of the Columbia river is the sturgeon. Little is known of its life history or migrations. Although it is probably not essential to the survival of the sturgeon that they move up and down stream at Bonneville, they may be included among the migratory fish. Very few were observed to pass through the fishways during the first season.
The eel-shaped creatures that frequently may be seen adhering to the side walls of the Bonneville fishways are properly called “lamprey”. They are commonly called “eels” but should not be confused with the Atlantic eel, which is not found on the Pacific side of the continents. Upon the basis of its primitive characteristics, including its sucker-mouth, cartilaginous skeleton, and lack of paired fins, it is classified by the scientist in a group just below the true fishes.
The life history and habits of the lamprey are essentially the same as those of the salmon. Like the salmon, it spans in fresh water, spends the greatest part of its life in the ocean, does not feed while making its spawning migration, and dies after spawning.
The lamprey is one of the most abundant species in the Bonneville fishways. An incomplete count of those that passed through the counting gates during the first season totaled more than 200,000. A significant proportion slipped between the bars of the counting station and passed without being counted.
Due to prejudice influenced mainly by its snake-like appearance, the lamprey is not commonly utilized as food. Nevertheless, it is considered to represent a potentially valuable resource that is worthy of protection.
The first season�s experience at Bonneville has shown quite large numbers of migrating fish among the species of so-called “scrap fish”, including suckers, squawfish, chubs, carp, and others. For the greater part of the time the fish of this group were more abundant in the fishways than were the salmon and trout.
Commercial Fishing
The Salmon, Steelhead Trout, Shad and Sturgeon form the basis of an extensive commercial enterprise. As the salmon start their migration toward fresh water they are caught in the ocean by hook and line. The fishing for salmon propagated in the Columbia River extends as far as British Columbia, even somewhat into Southeastern Alaska. It is estimated that this fishing takes as much as 7,000.000 pounds of Columbia River Chinook each year. After the fish enter the Columbia River they must avoid the perils of commercial fishery for a distance of about 180 miles. In this area thousands of fishermen, armed with gillnets, traps, seines, and dip nets annually catch from 24,000,000 to 40,000,000 pounds of fish. Those that escape the 140 miles of this intensive fishery use the Bonneville fishways in their progress upstream to the spawning grounds.
Site and Design of Bonneville Dam
The Bonneville Dam is located on the Columbia River just beyond the tide water, approximately 140 miles from the mouth of the river. At the site of the dam the river normally flowed into two channels separated by Bradford Island. The spillway portion of the dam is located in the north or main channel. The powerhouse spans the south channel. Only the water required for generating power and the operation of the navigation lock now passes through the south channel, all surplus river flow being discharged through the spillway. The water level above the dam is normally maintained at 72 feet above seal level. During the annual freshet, when the water level below the dam rises as much as 30 feet above its normal low water level, the water level above the dam may be raised to a maximum of 82 feet above sea level. The difference in water levels above and below the dam accordingly averages about 55 feet and varies between 66 feet and extremely low river flow and 30 feet at the crest of a high freshet. Backwater from Bonneville Dam extends approximately 46 miles upstream to a little beyond The Dalles, Oregon. This backwater is not, however, “slack” water. On the contrary, due to the volume of water in the river, and the narrow precipitous gorge through which is moves, there is always a substantial current present.
Types of Fishways
To give positive assurance of the passage of fish at all times, two independent types of fishways were installed by the Army Engineers, on the conventional, pool-type fishladder; the other a fish-lock, which operates on the principal of a navigation lock. There also was added a feature known as a “collecting system”, the function of which is to increase the effectiveness of the fishway entrances in attracting fish to them.
Fishladders. � Each fishladder consists of an inclined water passage, 40 feet wide, circling around the end of the dam from the lower to the higher water level. At intervals of 16 feet along this passage, there are cross partitions, 6 feet in height, the crest of each successive one of which is one foot higher than the one next below. Water flows down this passage, spilling over the successive cross partitions to form a series of pools. Fish attracted by this flowing water are readily able to pass from pool to pool in climbing to the higher level. The quantity of water flowing down the ladders is adjusted to an amount that induces the fish to swim rather than to jump from one pool to the next. In each partition between the pools there is a submerged opening, two feet square, through which a large proportion of the fish swim without at all rising to the surface.
Fish-locks. � The Fish-locks as installed at Bonneville Dam are identical in principle with navigation locks. Each lock consists of a vertical hydraulic chamber 20 feet by 30 feet in section. Near the bottom of the chamber, a gate controlled opening ten feet square communicates with the water below the dam. A similar opening near the upper end of the chamber communicates with the water above the dam. A conduit system entering the bottom of the chamber provides for filling and draining. In operation, the entrance gate first is opened and a moderate quantity of water admitted through the bottom of the chamber flows out through the entrance gate to attract fish into the chamber. The entrance gate then is closed and the chamber is filled by water admitted through the bottom. The exit gate then is opened, permitting the fish to escape to the river above the dam. A submerged grill that slopes downward toward the exit gate may be slowly raised beneath the fish to urge them toward the exit and assure their departure. The exit gate is then closed, the lift chamber drained, and the entrance gate opened for the commencement of a second cycle. The fish-locks are provided in pairs, in order that one chamber always may be open for the entry of fish.
Collecting systems. � The effectiveness of a fishway system in attracting fish to its entrance depends to a great extent upon the combination of the magnitude of its entrance and the quantity of water discharged through it. In order to obtain these advantages without the necessity of correspondingly increasing the magnitude of the fishways as a whole, there was added at Bonneville Dam a feature new to fishway design, which has been termed a “collecting system”. In principle the fishway adjacent to its entrance is expanded horizontally, vertically, or in both directions. Under the floor of this expanded area is a series of diffusing chambers through which auxiliary water supplied by a conduit system may be admitted at a controlled velocity. In this sway the normal flow of the fishway is augmented ten to fifteen fold to give at the entrance a flow of 2,000 to 3,000 cubic feet per second � the equivalent of a fair sized river.
Number and Position of Fishways
It was anticipated that fish approaching the Bonneville Dam would seek routes of passage at each end of the spillway dam and across the face of the powerhouse. Three sets of fishways accordingly were provided with entrances at these three points. Each set of fishways consists of a collecting system, a fishladder, and a pair of fish-locks. The fishladder and fishlocks connected with the same collecting system may be operated simultaneously or separately.
The fish-locks at the two ends of the spillway dam are embedded in the structure and form an integral part of the dam. The two ladders with entrances at the south end of the spillway and at the powerhouse join to form a single structure for the upper third of their course. The collecting system in the south channel has the form of a flume-like passage extending across the face of the powerhouse and having openings for the entrance of the fish distributed along it�s entire length. At its north end of this passage communicates with a fish ladder. At the opposite end are a pair of fish-locks and an opening through which the navigation lock may be used for the passage of fish.
An additional fishladder, designed primarily for downstream migrants but available for upstream migrants as well, has also been provided. From its entrance at the mouth of tanner Creek, about a half mile below the dam, it extends a series of long pools and typical ladder sections, to its exit just south of the navigation lock.
Downstream Migrants
Except as special provision might be made for other routes of travel, fingerlings would be expected to pass with the general flow of water through the spillway and the power wheels. Extensive laboratory and field tests indicate that there is little danger of injury to small fish passing through the Bonneville turbines. The propellers in the Bonneville power units are 23 feet in diameter, and rotate at a rate of 75 revolutions per minute. The minimum opening through which water must pass varies with normal operating conditions between the limits of one foot and three feet.
However, as a precaution to assure the safe passage of downstream migrants, four special bypasses have been provided with entrances located at points at which fish are most apt to reach the dam. It is commonly contended that fingerlings in their downstream migration shun the higher velocities in mid-stream and are found mainly in the quieter water along the shore. Bypass entrances accordingly have been placed as such points, one at each end of the spillway, a third between the powerhouse and navigation lock, and fourth south of the navigation lock. A trash sluice, with entrances distributed entirely across the face of the powerhouse, and the two fish ladders furnish additional favorable routes for downstream migrants.
Fish Counting
As a means of observing the success of the fishways, fish-counting stations have been installed in each ladder. Each counting station consists of a picketed barrier in which there are three gate controlled openings, two feet wide for the passage of fish. A submerged, white platform over which the fish must pass as they leave the counting gate aids the identification of species.
The counting gates remain closed except when an observer is present to count the fish. Experience has shown that there is very little movement of fish at night. Counting, there for, generally is limited to the hours of daylight, the gates being kept closed at night. During the peak of the run two or three counting station in each ladder are operated at one time. Each species of fish is counted separately and counts are recorded hourly.
During the first season actual count showed 271,656 Chinook, 74,989 Blueback, 15,298 Silver, 2,107 Chum Salmon, 106,884 Steelhead Trout, 2,213 other game fish, 5,321 Shad, 376,272 scrap fish (Sucker, Squawfish, Chubs, Carp, etc.), 3,102 White Fish, and 223,248 Lamprey passing over the counting stations on the way upstream.
Success of Fishways
It has been found that the fish slip by from pool to poll of the ladder with so great ease that they seldom are seen. Never has there been any evidence of accumulation of fish below the dam.
The daily counts of fish passing through the fishway have been compared to the daily commercial catches of salmon in the area immediately below the dam and at Celilo Falls, fifty miles above the dam. In this way it has been possible to trace waves in the abundance of fish, to observe that they passed the dam as rapidly as they arrived and that within about three days they had passed through the backwater area to Celilo Falls.
The fish counts, of course, speak for themselves in showing the large numbers of several species of fish that have passed the dam. Further evidence of the success of the fishways is found in the records of the five salmon hatcheries operated within thirty miles above the dam. These stations obtained an aggregate of 42,000,000 Chinook salmon eggs during the first season the Bonneville fishways were in operation. This is more than ten percent above the average for these stations.
