394 
On  River  Conservancy, 
originally  adapted  ; and  being  unable  to  hold  the  water  sent  to 
them  within  their  banks,  it  overflows  the  lower  lands.  This 
effect  is  enhanced  by  the  improvements  which  are  made  by 
riparian  proprietors  to  protect  their  land  from  flooding,  by 
embanking,  diminishing  the  flood-area  in  their  own  locality, 
and  driving  the  water  on  to  the  low  lands  of  their  neighbours. 
Again,  the  increase  of  population  and  the  demand  for  land  have 
caused  the  reclamation  of  large  tracts  which  were  once  commons 
and  peat  mosses.  These  were  formerly  in  an  undrained  state  with 
many  low  parts  ; and  while  dry  in  summer,  became,  after  heavy 
rain,  reservoirs  to  hold  the  rainfall  and  regulate  the  supply  to  the 
rivers.  The  stubbing  of  woodlands  has  had  the  same  effect,  as 
the  soil  in  which  trees  grow  absorbs  and  retains  an  immense 
amount  of  water. 
The  question  whether  tile-drainage  has  added  to  the  in- 
crease of  floods,  is  one  that  has  caused  a division  of  opinion  ; it 
being  maintained  by  some  that,  by  drying  the  land,  it  makes  it 
more  porous  and  absorbent,  and,  like  a dry  sponge,  ready  to 
receive  and  hold  the  rain.  If,  however,  under-drainage  does  not 
void  the  water  off  the  land  more  quickly,  of  what  use  is  it  ? 
Taking  two  arable  fields  situated  side  by  side,  one  drained  by 
tiles  and  the  other  undrained,  except  by  top  grips, — in  a wet 
season,  from  the  former,  after  a heavy  rain  the  water  will,  in  a 
very  short  time,  begin  to  run  out  of  the  pipes  into  the  ditches  in 
a continuous  stream  ; whereas,  from  the  undrained  land,  no  visible 
discharge  will  take  place.  On  the  former  land,  work  could  be 
resumed  in  a very  short  time  ; whereas,  on  the  latter,  if  clay,  it 
would  be  several  days  before  the  land  would  be  workable,  and 
only  when  by  the  evaporation  caused  by  the  sun  and  wind,  or 
by  slow  and  imperceptible  percolation  into  the  subsoil,  the  water 
due  to  the  rain  had  passed  away.  The  argument  that  pipe- 
drained  and  steam-cultivated  land,  by  being  rendered  more 
porous,  and  consequently  more  absorbent,  is  calculated  to 
hold  more  water,  is  good  so  far  as  it  relates  to  the  result 
in  dry  weather.  However,  floods  do  not  generally  occur 
under  these  circumstances,  but  only  after  a continuance  of  rain, 
when  absorbent  lands  have  become  saturated  and  the  natural 
level  of  the  water  in  the  ground  has  been  raised  to  the  level 
of  the  under-drains  ; after  this  has  taken  place  the  whole 
of  the  surplus  rainfall  must  be  discharged  more  rapidly, 
from  the  facilities  afforded  by  a perfect  system  of  drainage. 
On  land  undrained,  and  with  the  subsoil  not  broken  up  by 
cultivation,  the  rain  lodges  on  the  surface  and  in  the  furrows, 
and  slowly  finds  its  way  by  percolation  through  the  pores  of  the 
earth  to  ditches  choked  with  weeds,  and  so  arrives  at  the  river 
by  degrees  long  after  the  water  from  the  drained  land  has  passed 
