130 FP- f713- 

Page 1

MAINTENANCE REQUIREMENTS OF A FISH BARRIER NET SYSTEM

Authors: Thomas Plante, Michael Feldhausen, Dennis Olsen, and David Michaud

Wisconsin Electric Power Company

Milwaukee, Wisconsin

In response to environmental agency concerns regarding fish entrainment at hydroelectric plants in the upper

Midwest, Wisconsin Electric installed and tested a prototYPe barrier net system at its Pine Hydro Plant in June

1990. The barrier net system s functionality was monitored by company staff over the two year test period.

Specifically, the net's response to changes in flow , debris loading, and biofouling was noted by operation staff as

part of their daily routine. A contractor periodically assessed the efficacy of the net to prevent fish entrainment into

the power canal.

In anticipation of this study, company staff modified the existing log boom that protected the intake from large

debris. The boom was refitted with new decking, safety rails, and extra floatation (styrofoam billets). This exercise

cost approximately $2 800 in supplies and consumed nearly 160 hours of staff time.

In response to warmer summer conditions, biofouling became a significant concern, even in what could 

characterized as relatively unproductive waters. Physical removal of attached algae was attempted using long

handled stiff-bristle brushes, with limited success. Staff time devoted to this exercise averaged five hours per week.

Surface debris loading (e. , leaves) was successfully controlled by inducing a reverse flow through the net by

controlled spilling. In this situation, the flow through the plant was shut off and a spill gate close to the net was

opened. Experimentation demonstrated that a flow of 350 cfs was sufficient to induce a reverse flow through the

net. In addition, during the first year of the evaluation, net condition was observed monthly by divers who would

repair any observed tears in the net caused by old logs or beaver activity.

The company is committed to installing barrier net systems at two of its projects in response to conditions of new

licenses recently granted. Lessons learned with the Pine prototype system will be discussed. Implementing these

corrective measures should reduce anticipated problems with the permanent net systems.
Page 2

BARRIER NET DESCRIPTION AND DEPLOYMENT

INITIAL DESIGN AND DEPLOYMENT

In response to agency concerns regarding fish entrainment at company projects, the company commenced a fish

protection research project. Based on results from the Phase I feasibility study, the Pine Hydro Project was selected

as a site that could accommodate a barrier net system. The Pine barrier net was initially designed by Stone &

Webster Environmental Services (SWES) and was deployed in 1990 immediately downstream of an existing log

boom, as shown on Figure 1. Prior to net installation, the log boom was modified by company staff to allow safe

deployment of the barrier net from the downstream side without danger of overturning the boom walkway. New

foam buoyancy was added to the downstream side of the log boom. The foam billets carried the additional load

encountered during barrier net deployment and cleaning operations. The log boom modification costs included

approximately $2 800 in supplies and nearly 160 labor hours.

The barrier net was approximately 260 ft in length, with the height varying between 2 ft and approximately 35 ft.

The barrier net was fabricated to match the flowage bottom contour as closely as possible. An initial bottom survey

performed with a lead line dragged across the bottom indicated the presence of large debris projecting off the

bottom in the vicinity of the log boom. A diver survey was then performed to inspect the bottom and locate debris

which could have snagged in the barrier net and prevented the net from seating properly or being retrieved at a

later date. Prior to deployment, this debris was removed.

The barrier net was designed to extend from near the water surface to the bottom with up to two feet of bow (Figure

2). The net was intentionally installed with the top line set 12 to 18 inches below the surface to allow surface debris

(leaves, pine needles, sticks) to pass freely over it. The net material was knotted nylon and the mesh was 1/2 inch

square (I inch stretch). A 3-foot apron fitted with a lead line was affixed to the bottom line of the net to improve

the seal at irregularities along the bottom.

The top of the barrier net was tied back at 10 foot intervals to the wire cable which anchors the log boom.

Inflatable floats (40 pound buoyancy) were attached to the top of the barrier net above each of the anchor weights

along the bottom line. The log boom is securely anchored to the shore and dam and the logs are structurally sound

so that forces attributable to flow through the net were transferred to the log boom anchors.

The bottom of the barrier net was held in place by iron blocks (80-100 Ibs each) spaced at 10 to 20 foot intervals

depending on depth. Nylon lines, feeding from the log boom down through an eyelet in each of the anchors, were

used to deploy and hold the bottom of the barrier net in place, similar to an upside-down flagpole line. These lines

were tied off to the log boom superstructure.

One end of the barrier net was attached to the dam face by mounting a vertical steel bracket (in three sections) to

the darn that allowed four vertical steel sections ("T" shaped in cross-section), with the net attached to them, to be

slid down a groove in the bracket. The netting was bundled and cable-tied to holes drilled in the "T" shaped steel

pieces. The bracket was mounted to the dam face using an underwater drill and Hilti bolts. The shore end of the net

was secured to the log boom cable anchor.

At the end of the 1990 sampling season, the barrier net was dropped to the bottom of the reservoir and secured in

place for the winter by divers.

1991 DESIGN AND REDEPLOYMENT

The barrier net was redeployed from its winter storage position for the 1991 evaluation. The orientation and

position of the deployed net was the same as in 1990. As ice-out was occurring, SWES and company personnel and

several divers raised and resecured the net. Most of the net was redeployed with the plant on line. However, the net
Page 3

section between the log boom and the dam had to be redeployed with the plant shut down due to excessive drag

forces on the net. 

A complete inspection of the net, support lines, log boom, was performed. All logs, branches or other debris that

had come to rest on the net or any other element of the support system over winter were removed. Divers verified

that all net anchors were in approximately the same location as when the net was dropped at the end of 1990. The

anchor pull-down lines which had been secured to the bottom in the fall of 1990 were brought to the surface and

reattached along the log boom. Additional buoys were used on the top of the entire barrier net in order to keep the

top of the net within approximately six inches of the water surface. Based on the 1990 entrainment monitoring

results, several modifications were made to the net design, as described below.

In 1990, many small fish were thought to have passed over the top of the barrier net, especially in the area closest

to the dam. Therefore, a new surface net was used to supplement the portion of the existing barrier net system in

this area. The surface net was positioned two feet upstream of the original barrier net between the dam and the log

boom. The surface net was nine feet deep, about 90 feet long, and had toggle floats sewn into the top line every two

feet. The mesh size was the same as that of the main barrier net Y2 inch square. The top of the surface net was tied

to the logboom and to a bracket mounted on the damface two feet upstream of the main barrier net bracket. The

surface net float line was therefore positioned upstream of the cable and its bottom line passed under the barrier net

support cable and spring lines. The bottom of the surface net was attached every three feet to the top line of the

barrier net with cable ties, then the two nets were stitched together every six inches with 160 lb. net mending

twine. This net deployed easily and functioned as anticipated in its design in that the top line of the net floated at

the water surface and physically prevented fish passage

The buildup of algae and other fouling material on the original net in 1990 led to an evaluation of antifouling

agents in 1991. Three portions of the new surface net were coated with one of three different types of antifouling

material. These coatings were Flexabar Waterbase (the standard coating applied to the net by the manufacturer),

Flexabar Antifouling, and Seagrove Soft Copper (Base #1). The surface net was installed with the Flexabar

Waterbase panel closest to the dam, the Seagrove Soft Copper (Base #1) panel in the middle, and the Flexabar

Antifouling panel nearest the log boom.

NET MAINTENANCE AND INSPECTIONS

After the barrier net was deployed in both years, the net was inspected by divers for snags, tears or gaps between

the lead line seal and the bottom. The divers removed debris to improve the seal along the lead line and prevent

abrasion of the net. The seal at the shore and dam were also inspected. The divers swam along the face of the net

inspecting for any holes or debris in the net. Finally, the surface of the net was inspected to check all the

connections to spring lines and buoys. In 1991, the surface net was inspected for the integrity of connections to the

main barrier net as well as to ~onitor the degree and nature of fouling.

Diver inspections of the net' s condition were performed during each monthly trapnet sampling period. A log of

each inspection was organized to record the condition of the net at the 12 locations shown on Figure 3. Starting in

May 1991, a 250-watt underwater light powered by a portable generator was made available to the divers for their

inspections. The 300-foot power cable allowed the divers freedom to inspect the entire net with improved visibility.

In 1990, tension gauges were initially installed on three of the spring lines between the log boom and the barrier

net top line to monitor debris loading and subsequent strain on the net support system. During the initial year of

the study, periodic tension readings were taken to document th~ rate of debris loading and/or biofouling. In

addition, as drag forces on the net increased over the course of the study, the clearance between the water surface

and the top of the net was monitored using buoy submergence as a gauge. This information was useful in

estimating the frequency of net cleaning that would be required for future installations. During the interim periods
Page 4

when biological sampling was not being conducted, the net was monitored by company personnel, primarily for debris accumulation. 

VELOCITY MEASUREMENTS

A Swoffer Instruments Model 2100 velocity sensor was used to measure velocities along the inside of the barrier

net, along transects between the barrier net and the dam, and in the canal intake during each trapnet sampling

period in both years. The locations of the transects are shown on Figure 4. The Swoffer sensor provided accurate

velocity measurements from 0. 1 to 24 fps. It consisted of a propeller mounted either on a U. S. Top-Set Wading

rod or a downrigger and a digital readout indicator. It had the capability to average readings over an adjustable 5 to

90 second period. An extension was added to the wading rod for readings below five feet. The extension allowed

readings to be obtained to a depth of 13 feet. Beginning in August of 1990, a downrigger system for deep

deployment of the flow meter was used to obtain velocity readings to the bottom. The downrigger was designed to

orient the meter into the current. Measurements were taken at two foot intervals.

The velocity information was used to identify areas prone to debris loading and/or subject to excessive hydraulic

forces, and to assess alternative net locations for possible future consideration. Velocity distributions were mapped

at a variety of flows through the plant.

BARRIER NET PERFORMANCE

The initial installation of the barrier net in June 1990 and the redeployment of the net in April 1991 took place

with only minor difficulties. However, installations would not have been possible without diver support.

During July 1990, a test was conducted to determine the feasibility ofbackflushing the barrier net by reversing flow

direction. Flow through the power canal was discontinued and a spillway tainter gate (Number 2) was opened (see

Figure 1). This operation reversed the flow through the net. During the backflushing, the section of the net nearest

the darn billowed towards the tainter gate while the rest of the net hung slack. the divers and surface personnel

observed small debris, included leaves, twigs, and some algae, floating away from the net, primarily in the area

closest to the dam. Upon resumption of power generation and closing of the tainter gate, the net returned to a

normal position. these test results demonstrated that this method could be an effective, economical way of cleaning

the barrier net.

The integrity of the seal along the bottom and dam remained intact throughout the two-year study. During the fall

of 1990, the top of the net was the same distance under the surface as in other months under low plant flow

conditions. However, at high flows, the buoys were completely submerged. Operations staff interpreted this finding

as an indication of significant net fouling. During the fall leaf period, Operations personnel backflushed the net

o!le or two times a week in order to minimize leaf buildup.

By September 1990, silt and algae had built up to a Y:z- to %-inch thickness along the top 10 feet of the net. In

addition, sparse clumps of a lighter green, long (8 to 12 inches) and stringy algae occurred on the net. Holes were

infrequently found and were generally small (5 to 8 inches). Organisms living on or near the net had also

increased. Sponges, hydro ids, snails, amphipods, larval insects and small fish were found either on the nets, the

buoys or in the surface layer near the net. Following a backflush during the September inspection, the divers

performed a second. quick inspection of the net. The degree of blockage caused by the algae remained the same.

However, there generally was a decrease in the amount of leaves and twigs on the net. The leaves appeared to come

off the net and si~ to the bottom since the divers reported an increase in the pile of leaves along the bottom of the

net. Leaves near the surface of the net that were enmeshed in the algae tended to remain in place after

backflushing. Following the backflushes there was a slight increase in the buoyancy of the buoys along the top of

the net. However, the tension gauges did indicate a drop in the drag force on the net as a result of the net cleaning

efforts each month.
Page 5

In November 1990, the top three feet of the net along the log boom was lifted out of the water and cleaned with a

scrub brush in preparation for bottom deployment of the net for the winter. the amount of fouling growth was not

reduced from October, even though water temperatures had reached 4OC and there was reduced photoperiod. A

two hour backflush was performed to remove leaves, during which time the remainder of the net was scrubbed,

both along the surface from a boat and at greater depths by the divers with handheld scrub brushes. No holes were

reported, and the general condition of the net was exc~llent. With the plant shut down, the net was detached from

the dam and all the buoys and spring lines removed. A lead line was attached 18" below the top line to help hold

the net on the bottom, while small foam floats were placed on the top line to assist in net retrieval in the spring.

The pull-down anchor lines were detached from the log boom and secured on the bottom. Thirty feet of the net was

detached from the shore and bundled up and lowered to the bottom in 6 feet of water so that it would not become

imbedded in surface ice. Divers assisted in lowering the net to the bottom.

Before the barrier net was redeployed in April of 1991, divers inspected the bottom for any debris that might have

damaged the net or hinder its redeployment. After the barrier net was raised, divers inspected it for snags, tears, or

gaps between the lead line seal and the bottom. The divers removed several small sticks. Nearly all of the algal

growth and fouling present on the net at the end of 1990 had been removed from the net probably by microbial

action. Except for a 1 to 2 foot wide band near the top of the net, the net was nearly as clean as when it was

installed in 1990. In the week after the net was redeployed only a very fine buildup of suspended sediment was

observed on the upper part of the net and this was easily dislodged by moving the net slightly.

Debris started to accumulate in the apex of the bow in the net by the May inspection date. Several small holes (2 to

5 inch) were sewn shut. Silt was deposited each month on most of the net but came off by shaking the net. 

places, strands of algae with adhered silt extended up to six inches, primarily to a depth of 3 to 4 feet from the

surface. A few patches of sponge were observed, mostly towards the shore.

As in 1990, backflushing removed sticks, twigs, and leaves but did not greatly reduce the blockage of the net, since

algal and silt fouling were largely responsible for the blockage. The effectiveness of the backflush was most evident

near the dam due to the close proximity to the open spillway gate and lest noticeable near the'shore. Cleaning the

net with brushes was effective in removing more than 75 percent of the algae and silt from the top 8 to 10 feet 

the net.

By May, 1991 , the new surface net had collected a lot of surface debris, particularly near the dam. The degree of

fouling among the three treated net panels was noticeably different. The Flexabar Waterbase panel near the dam

(the same material as the original barrier net) was the most fouled of the three panels with algae and silt. The

Seagrove Soft Copper (Base # I) panel in the middle was intermediate in degree of fouling, having uniform but less

dense algal growth and silt than the Flexabar Waterbase panel. The Flexabar Antifoulant panel near the log boom

was slightly less fouled than the other two, having interspersed patches of net with no algal growth.

Throughout the remaining months, the three treated surface net panels continued to show the same degree of

difference in fouling noted in May. However, the degree of fouling continued to increase on all three panels

through the June and August inspections. Abundant stringy algae was observed on the dam-side panel, but only

sparsely on the other two panels. The middle panel (Seagrove) had a little more algae and silt accumulation on the

net mesh than the lob boom panel. By September, the Flexabar Antifoulant and Seagrove-treated panels were

nearly similar in degree of fouling. The regular Flexabar treatment nearest the dam remained the most fouled.

Numerous small fish (minnow and shiners) were observed swimming along the downstream side of the surface net.

During the September 1991 sampling period, the barrier net was not backflushed nor inspected by divers. Surface

observations showed a substantial accumulation of silt and algae on the net, blocking 90 to 100 percent of the net

mesh.
Page 6

In late October 1991 , a quick inspection and cleaning of the net was performed prior to lowering the net to the

bottom for a second year of winter storage. The net was in excellent condition although heavily fouled to the extent

that the buoys between the log boom and the dam became submerged under high flow conditions. Following

cleaning and backflushing, the net was lowered to the bottom using the same methods employed in 1990. The net

material showed no visible signs of degradation after two years in the water. The antifouling treatments on the

surface net were effective: both the Flexabar Antifouling and Seagrove Soft Copper panels showed less fouling

than the Flexabar. Waterbase panel.

VELOCITY MEASUREMENTS

Velocity mapping (Figure 4) confirmed earlier estimates that velocities along the net would be less than 0.5 fps and

even a low as 0. 1 fps. velocities varied by plant flow rate, depth, and location. Velocities behind the barrier net

were highest on the surface during low flow periods (Figure 5) and around the periphery (sides, bottom, shore and

dam) during the high flow periods (Figure 6).

Flows along the transect from the log boom to the intake canal opening showed a definite increase in velocity

toward the intake. Velocities along this transect under low flow and high flow conditions are shown in Figures 7

and 8, respectively.

Flow velocities along a transect between the middle of the log boom and the dam under low flow and high flow

conditions ranged from less than 0. 1 ft/sec to about 0.4 ft/sec with no clear trends over distance or depth.

Flow velocities across the canal opening under low flow and high flow conditions ranged from generally less than

0 ft/sec to as high as 7.0 ft/sec.

DISCUSSION

The barrier net design and installation procedures require minimal modifications for long-term use. However, to

enhance net inspections and access, the net segment between the existing logboom and the dam will be outfitted

with a new logboom section.

During the two-year study period, the integrity of the net was maintained with few exceptions. However, it is clear

from the diver inspections conducted during this two-year study that the porosity of the barrier net was

considerably enhanced when it was "scrubbed down" with brushes. In addition, the surface net installed in 1991

revealed that the Flexabar Antifouling net coating reduced biofouling when compared with the standard net

coating. With less fouling of the net, there was reduced strain on the spring line, anchor, and buoy systems, as well

as the mesh material itself. Furthermore, backflushing of the net was effective in reducing net loading, particularly

during the autumn leaf fall period. -

Storage of the net on the bottom for the winter appears to be an ' appropriate technique. The net remained in place

debris covering was minimal and no deterioration appears to have occurred. In addition, nearly all of the biological

fouling died so that it sloughed off as the net was reinstalled. Reinstallation in the spring went smoothly. The

additional surface net was installed easily and could provide a complete physical blockage of the water column

between the log boom and dam.

Velocities along the barrier net remained well below 0.5 fps even under heavy fouling and maximum plant flow. It

seems that there was some vertical modification of velocity as the net became plugged along the top 15 feet. As the

net area near the surface became clogged, more water passed through the net at depths of 15 to 20 feet than was

measured when the net was unfolded. It should be noted that at low flows, the velocities at the entrance to the

power canal did not represent velocities that would commit fish to passage. As velocities increased, the probability

of committed fish passage increased.
Page 7

A comparison of the entrainment monitoring data before and after the barrier net was installed demonstrates that

the barrier net was successful at reducing the number of fish passing into the intake canal (Figure 9). The few

samples in which high numbers of fish were collected were, in most cases, due to young-of-the-year fish moving

along the face of the dam and ultimately over the barrier net. The low numbers of bottom and mid-water adult

species caught in the intake trapnet also indicated that the barrier net was effective in limiting fish passage into the

power canal.

CONCLUSIONS

Based on the results of this two-year study, the following conclusions can be drawn:

The barrier net design and installation procedures allowed for a successful deployment. Minor improvements

could be obtained with small modifications to equipment and procedures.

The barrier net substantially limits the passage of larger fish into the intake canal, based on a comparison of

trap net and reservoir survey data.

The occasional presence of large debris did not impair the function of the net.

Backflushing leaves and debris from the upstream surface of the barrier net by shutting off flow to the plant

and opening a tainter gate near the net appears feasible as a long-term maintenance technique for unattached

debris. Flows through the tainter gate in excess of 300 cfs for a period of at least one hour are required to

induce flow reversal through the net.

Algae growth and macroinvertebrate use of the net occurred within two months of deployment, suggesting that

a more effective antifouling substance must be used on the net for future deployments. Routine "brushings

may not be possible due to reduced staff availability.

Placement of the net on the bottom for winter storage is a relatively easy process, requiring less time and effort

than the initial deployment of the net. Placement on the bottom also allows for easy reinstallation in the spring

and has the added benefit of using naturally occurring microorganisms to remove fouling growth.

Reductions in small fish entrainment will require use of a finer mesh net overlay across the upper 10 feet of

net. In addition, the top of the net should be attached to the log boom cable to keep the net high in the water

column.

ACKNOWLEDGMENTS

The authors would like to acknowledge the significant assistance provided by the entire Operations and

Maintenance staffs of Wisconsin Electric s Hydro Division, located in Iron Mountain, Michigan, but especially

Richard Meinecke and Charles Schmidt.

We also gratefully acknowledge the substantial efforts of SWES staff, especially Ned Taft, Richard ("Ice Man

Marks and Paul Martin. Without their dedication and sense of professionalism, this project would not have

succeeded.

G:\BU _DATA \FO\P SBAN1 O\WORDWIN\MICHAUD\BARRINET. DOC
Page 

Dam

B2...'Tier Net Canal

Intake

Flow

PINE RIVER

F:w

Not To Scale

Figure 1

Schematic layout of Pine Barrier

Net Study Site
Log Boom Buoy

Page 9

Barrier Net

Deployment!

Retrieval

line

......

Flow

Not to Scale

Bottom

Figure 2

Cross section view of

, barrier net installation

Barrier Net
Shore

Figure ~

Ive I r nspection Stations

Page 10

Dam

Power Canal

Entrance
Shore

Canal Intake

'I ,I ,

Ve oclty Measurement I Transect I 

I /' , I 

Velocity Measurement

Transect Behind Net

Canal Intake

Volocity

Measurement

Figure 4

Standard Locations of Velocity Measurements

Velocity Measurement

Transect
FIGURE 5

FLOW VELOCITIES ALONG THE DOWNSTREAM SIDE OF THE BARRIER

NET DURING A TYPICAL LOW-FLOW PERIOD (AUGUST 1991)

00' .

11-

:: 15

.....

'-" 1 7

19 0..

-----------. 0 0

Bottom

Shore 1 08 121 134 147 157 167 177 187 197 207 217 227

Approximate distc nce (ft.)

FIGURE 6

FLOW VELOCITIES ALONG THE DOWNSTREA' 1 SIDE OF THE BARRIER

NET DURING A TYPICAL HIGH. FLOW PERICD (SEPTEMBER 1991)

:: 15

.:::.. 17

:E 19

0..

'" 21

Shore

0,:

.

0 I

0 I

.

32 . 00 Bottom 46 . 24 

95 108 121 134147 157 167 177 187 197 207 217 227

Approximate distance (ff.) 
Page 13

FIGURE 7

FLOW VELOCITIES ALONG THE TRANSECT FROM THE LOG BOOM TO THE

CANAL OPENING DURING A TYPICAL LOW- FLOW PERIOD (AUGUST 1991)

.40

Bottom ----:- 15

:::

a..

Log . 5

800m Sfafion Dam

FIGURE 8

FLOW VELOCITIES ALONG THE TRANSECT FROM THE LOG BOOM TO THE

CANAL OPENING DURING A TYPICAL HIGH- FLOW PERIOD (SEPTEMBER 1991)

.47 I. 1 6

1.20

.41 .78 1.21

~ 1-

.44 .42 .41 1.20

.49 1.24

.40

BaHam

:: 15

'--" 17

Log

Boom Station Dam
700

fish/hour

flow 600

500

(j)

400 ~

300 C

0...

200

100

Nov.

Figure 9

Fish/Hour vs Plant Flow

1990

Barrier Net Deployed

....

::J 20

..c

~ 15

....

is 20

..c

~ 15

April

1991

fish/hour

flow

. . note: the year for this month is 1989

# . note: sampling did not occur in these months

Page 14

700

600

500

(j)

400 ~

300 C

0...

200

100
Plante97.doc, 08/14/98, 3:31 PM /3 

Maintenance Re uirements of a Fish Barrier Net S stem. 1997.

T. Plante, M. Feldhausen, D. Olsen, and D. Michaud

In the summer of 1990, Wisconsin Electric installed and tested a prototype barrier net system at

the Pine Hydro Plant. Part of the responsibility of the operation staff was to note the net'

response to changes in flow, debris loading, and biofouling (Plante et aI., 1997).

With concern of heavy debris, the existing device that protected the intake from debris was

modified. Safety rails and new decking were added to the device, also known as the "log boom

Additional flotation was also added. The estimated cost and man hours for this task were $2 800

and 160, respectively (Plante et aI., 1997).

The problem ofbiofouling was solved to some extent by using a long brush to scrape the net. 

for heavy debris surface loading, reverse flow could be induced by reaching a flow of 350 cfs.

This would control some of the debris (Plante et aI., 1997).

As for the specifics on the barrier net, it was approximately 260 feet long and varies between 2

and 35 feet high. The top of the net is about 12 to 18 inches below the surface for allowance of

debris to pass over freely. Attached to the bottom was a 3 foot apron fitted with a lead line. The

bottom of the net was held in place by using 80-lb iron blocks, spaced about every 10 feet apart

(Plante et aI., 1997).

The net was modified come 1991. A surface net was added, working along with the existing

barrier net system. This was placed upstream from the original net, at approximately 2 feet. A

protective coating of antifouling substance was applied to the new net (Plante et aI., 1997).

Along with a new net, new inspection methods were now performed. Inspections of the nets

were made by a diving team every month for the sampling period. Observations were recorded

and it was then estimated what the necessary frequency of cleaning would be (Plante et aI.

1997).

For velocity measurements, a Swoffer meter was used. The points were taken inside of the

barrier net (Plante et aI. , 1997).

In the fall of 1990, it was noted that there was present an algae build up of 3/4" along the top 10

feet of the net. The fouling of the separate panels of net were slightly different among the three.

The panel which had been coated with antifouling was slightly less fouled. All things

considered, the net was in excellent condition (Plante et aI., 1997).

As stated before, backflushing seems to have been a beneficial method for cleaning twigs and

leaves off of the net. Cleaning the net with the long handle brushes added to the efficiency of the

net. It removed about 75 % of the algae and silt in the top 10 feet of the net (Plante et aI. , 1997).

It was concluded that overall, the barrier net design was easy to install and easy to modify. The
Plante97.doc 08!l4/98 3 :31 PM

net does limit however the passage of large fish. There are occasional high periods of debris, but

nothing that seriously impaired flow condition. Reversal of the flow is an effective procedure in

cleaning the net, when flows exceed 300 cfs. Brushings will be necessary to keep net face clean

and free of debris. The placement of the net at the bottom of the channel is an ideal storage

procedure. Microorganisms will rid the net of any fouling algae (Plante et aI., 1997).