378
G . T. CSANADY
about 1 m wide, their linear density being there about 1 per 3 m length of
beach, in some places 3 per 1 m. Although the waves oficn placed a fish on
the beach, they soon moved it again, not one of them being retained on the
beach for more than a fraction of a minutu. The beach was sand to fine
gravel, having a slope of about 1 : 15. At the w e time there was a band of
dead alewives, a few days old, lying about 15 m from the shore, on land
about a meter above lake level. These had evidently been deposited by larger
waves, in the high linear density of 10 to 30 alewives per meter.
Those alewives floating in from the lake which were not quite dead yet
could be seen to bled and exude a jelly-like substance either at the gills or at
one of their fins. They also swam in countmcloclrwise circles of about 30 cm
diameter as if completely disoriented. Plwumably, these were the cffkcts of
thermal shock which they experiencGd on rwimming into warm coastal
waters.
Later during the day the waves bacarne somewhat higher (10 and even
15 cm amplitude), but there was still no permanent retention of fresh alewives on the beach. Theentire school had by late ahrnoon concentrated into
a nearshore band some 10 m wide (and several kilometres long, the exact
extent being unknown) with a linear density of 5 akwives par meter or more.
A longshore current was moving these northward at a speed of the order of
10 cm see- I.
In the evening (6 P.M. or so) the wave amplitude decreased again to a few
cm. At this time all at once some akwives were permanently deposited in a
density of about 1 per m, in about one hour. Onc may legitimately conclude
that, as the waves were diminishing in hciht, some akwives could be left
high and dry by a larger wave which was no longer repeated.
There can in fact be: littk doubt that the beach deposition of alewives is
accomplished by wave-orbital water movemenu. Thc retention of each such
floating object on the beach is a chance event, the probability of which must
be proportional to the concentration of alewives (number per square meter
x ) near the shore. The intensity I of p e n n a m t deposition (number per
meter shoreline per second) also depends on the wave amplitude, and
presumably on the rate at which this derrtaesJ. In analogy with other masstransfer problems we may write
(1)
I = v,x
where v, is a mass transfer coefficient or deposition velocity (cm sec-I)
about which we can say little. The observations just described suggest a
deposition velocity of about 0.05 cm sec- ', cawed by such very small waves
as they died out. Presumably, larger waves give rise to a much higher deposition velocity at their time of decay; the band of alewives 15 m from shore
suggests v, = 1 cm sec-I. if the surface concentration was the same when
G . T. CSANADY
about 1 m wide, their linear density being there about 1 per 3 m length of
beach, in some places 3 per 1 m. Although the waves oficn placed a fish on
the beach, they soon moved it again, not one of them being retained on the
beach for more than a fraction of a minutu. The beach was sand to fine
gravel, having a slope of about 1 : 15. At the w e time there was a band of
dead alewives, a few days old, lying about 15 m from the shore, on land
about a meter above lake level. These had evidently been deposited by larger
waves, in the high linear density of 10 to 30 alewives per meter.
Those alewives floating in from the lake which were not quite dead yet
could be seen to bled and exude a jelly-like substance either at the gills or at
one of their fins. They also swam in countmcloclrwise circles of about 30 cm
diameter as if completely disoriented. Plwumably, these were the cffkcts of
thermal shock which they experiencGd on rwimming into warm coastal
waters.
Later during the day the waves bacarne somewhat higher (10 and even
15 cm amplitude), but there was still no permanent retention of fresh alewives on the beach. Theentire school had by late ahrnoon concentrated into
a nearshore band some 10 m wide (and several kilometres long, the exact
extent being unknown) with a linear density of 5 akwives par meter or more.
A longshore current was moving these northward at a speed of the order of
10 cm see- I.
In the evening (6 P.M. or so) the wave amplitude decreased again to a few
cm. At this time all at once some akwives were permanently deposited in a
density of about 1 per m, in about one hour. Onc may legitimately conclude
that, as the waves were diminishing in hciht, some akwives could be left
high and dry by a larger wave which was no longer repeated.
There can in fact be: littk doubt that the beach deposition of alewives is
accomplished by wave-orbital water movemenu. Thc retention of each such
floating object on the beach is a chance event, the probability of which must
be proportional to the concentration of alewives (number per square meter
x ) near the shore. The intensity I of p e n n a m t deposition (number per
meter shoreline per second) also depends on the wave amplitude, and
presumably on the rate at which this derrtaesJ. In analogy with other masstransfer problems we may write
(1)
I = v,x
where v, is a mass transfer coefficient or deposition velocity (cm sec-I)
about which we can say little. The observations just described suggest a
deposition velocity of about 0.05 cm sec- ', cawed by such very small waves
as they died out. Presumably, larger waves give rise to a much higher deposition velocity at their time of decay; the band of alewives 15 m from shore
suggests v, = 1 cm sec-I. if the surface concentration was the same when