﻿146 
  Transactions. 
  — 
  Miscellaneous. 
  

  

  that 
  the 
  town 
  of 
  Blenheim 
  has 
  been 
  saved 
  by 
  this 
  invention. 
  Of 
  all 
  the 
  

   money 
  spent 
  in 
  conservation 
  and 
  attempts 
  to 
  divert 
  the 
  stream, 
  these 
  log- 
  

   dams 
  only 
  remain, 
  and 
  when 
  thrown 
  up 
  shingle 
  can 
  be 
  retained, 
  no 
  danger 
  

   need 
  be 
  feared 
  for 
  the 
  future. 
  It 
  will 
  thus 
  be 
  seen 
  that 
  the 
  great 
  problem 
  

   of 
  how 
  to 
  divert 
  the 
  current 
  and 
  make 
  a 
  bank 
  of 
  shingle 
  where 
  it 
  can 
  be 
  

   utilised, 
  has 
  been 
  solved 
  in 
  one 
  of 
  the 
  most 
  dangerous 
  and 
  rapid 
  rivers 
  in 
  

   New 
  Zealand. 
  Unfortunately 
  the 
  conservation 
  of 
  rivers 
  here 
  is 
  in 
  the 
  hands 
  

   of 
  a 
  Board 
  elected 
  by 
  the 
  settlers 
  from 
  among 
  themselves, 
  and 
  such 
  bodies 
  

   are 
  not 
  only 
  slow 
  to 
  see, 
  but 
  timid 
  in 
  admitting 
  the 
  merits 
  of 
  a 
  new 
  idea. 
  

   To 
  make 
  the 
  matter 
  clearer 
  than 
  can 
  be 
  done 
  by 
  written 
  description 
  I 
  forward 
  

   a 
  small 
  model 
  of 
  the 
  invention. 
  

  

  Aet. 
  XII. 
  — 
  On 
  Beach 
  Protection. 
  By 
  W. 
  D. 
  Campbell, 
  Ass. 
  Inst. 
  C;E. 
  

  

  Plate 
  III. 
  

   [Read 
  he.fore 
  the 
  Westlancl 
  Institute, 
  ISth 
  July, 
  1878.] 
  

   The 
  encroachments 
  of 
  the 
  sea 
  on 
  the 
  sandy 
  ridge 
  upon 
  which 
  a 
  portion 
  of 
  

   the 
  town 
  of 
  Hokitika 
  is 
  built, 
  have 
  often 
  been 
  very 
  considerable 
  during 
  

   temjjestuous 
  weather, 
  and 
  at 
  times 
  have 
  created 
  no 
  unusual 
  amount 
  of 
  

   alarm 
  among 
  the 
  inhabitants 
  of 
  Eevell 
  Street. 
  The 
  subject 
  of 
  beach 
  pro- 
  

   tection 
  will 
  therefore 
  be 
  of 
  interest 
  and 
  importance 
  to 
  many 
  present, 
  and 
  I 
  

   propose 
  to 
  briefly 
  discuss 
  it, 
  prefacing 
  my 
  remarks 
  by 
  a 
  glance 
  at 
  the 
  

   conditions 
  presented 
  by 
  waves 
  in 
  accumulating 
  and 
  removing 
  beaches. 
  

  

  The 
  movements 
  of 
  shingle 
  and 
  sand 
  along 
  the 
  coast 
  are 
  due 
  to 
  the 
  

   waves, 
  whose 
  direction 
  is 
  determined 
  by 
  the 
  prevailing 
  .wind, 
  but 
  tidal 
  

   currents 
  sometimes 
  indirectly 
  affect 
  their 
  action 
  by 
  subduing 
  or 
  increasing 
  

   the 
  waves 
  according 
  as 
  they 
  may 
  be 
  with 
  or 
  against 
  their 
  direction. 
  The 
  

   action 
  of 
  the 
  waves 
  may 
  be 
  taken 
  to 
  be 
  of 
  three 
  kinds 
  :* 
  — 
  1st. 
  The 
  

   accumulative 
  action, 
  which 
  heaps 
  up 
  the 
  particles 
  against 
  the 
  shore. 
  

   2nd. 
  The 
  destructive 
  action, 
  which 
  breaks 
  down 
  the 
  accumulations 
  pre- 
  

   viously 
  made. 
  3rd. 
  The 
  progressive 
  action, 
  which 
  carries 
  forward 
  the 
  

   pebbles 
  and 
  sand 
  in 
  a 
  horizontal 
  direction. 
  

  

  The 
  difference 
  between 
  the 
  first 
  and 
  second 
  actions 
  is 
  determined 
  by 
  

   the 
  rate 
  of 
  succession 
  of 
  the 
  waves 
  ; 
  for 
  when 
  they 
  break 
  upon 
  the 
  shore 
  so 
  

   rapidly 
  as 
  to 
  over-ride 
  each 
  other, 
  a 
  continuous 
  downward 
  under-current 
  is 
  

   produced 
  and 
  the 
  destructive 
  action 
  commences. 
  The 
  progressive 
  action 
  

   takes 
  place 
  when 
  the 
  waves 
  impinge 
  obliquely 
  upon 
  the 
  shore. 
  

  

  * 
  See 
  "Observations 
  ou 
  the 
  Motions 
  of 
  Shingle 
  Beaches," 
  by 
  H. 
  B. 
  Palmer, 
  O.E.( 
  

   F.B.S., 
  Phil. 
  Trans. 
  Royal 
  Society, 
  1834, 
  Part 
  1. 
  

  

  