and  the  Cause  and  Prevention  of  Floods. 
409 
steps,  and  they  need  not  necessarily  be  perfectly  watertight,  the 
object  being  to  equalise  the  downward  flow  of  the  stream  as 
well  as  storage.  Such  reservoirs  scattered  over  the  tributaries 
of  a river  would,  while  affording  a supply  of  water,  tend  to 
equalise  the  downward  flow  in  heavy  rains,  and  check  to  a 
certain  extent  the  liability  of  the  main  streams  to  floods. 
To  prevent  flooding  entirely  by  means  of  reservoirs  is  utterly 
impracticable.  The  enormous  area  required  to  hold  the  flow  of 
even  a small  river  would  involve  a waste  of  land  that  would 
be  utterly  out  of  proportion  to  the  damage  done  by  flooding,  or 
to  other  means  that  might  be  adopted  for  securing  the  same 
end.  In  the  original  design  for  the  drainage  of  the  Fens  large 
tracts  of  land  were  left  at  the  lower  pares  of  the  rivers,  and 
running  parallel  with  them,  the  flood  banks  being  set  a con- 
siderable distance  back  from  the  channel, — these  “ Wash-lands  ” 
being  intended  as  receptacles  of  the  water  in  times  of  flood. 
Now,  owing  to  obstructions  which  have  been  made  at  their  lower 
ends,  these  form  large  reservoirs,  which  are  filled  when  the  main 
channel  is  insufficient  to  carry  off  the  downfall  water.  The 
washes  on  the  Nene  and  Welland  cover  an  area  of  5000  and 
3000  acres  respectively  ; and  although  these  rivers  drain  only 
a small  tract  of  comparatively  flat  country,  yet  when  these 
washes  are  covered  four  feet  deep,  they  only  make  provision  for 
a fall  of  a little  over  one-third  of  an  inch  of  rain.  This  fact 
should  be  sufficient  to  show  that  it  is  out  of  the  question  to 
depend  on  reservoirs  alone  as  flood-regulators,  as  has  so  frequently 
been  advocated. 
If,  in  the  anxiety  to  provide  a remedy  for  floods,  the  river 
channels  are  so  deepened  and  improved  that  the  water-level  of 
the  soil  is  lowered  without  adequate  provision  for  holding  it  up 
in  summer,  the  consequences  may  be  found  to  be  very  serious. 
The  soil  will  then  become  so  drained,  that  the  moisture  will 
sink  so  far  below  the  roots  of  the  plants  that  capillary  action 
will  fail  to  bring  it  to  them.  A great  deal  of  undeserved  blame 
has  been  thrown  upon  millers  for  holding  up  the  water  in  the 
rivers  for  working  their  mills  ; but  there  can  be  no  question  that 
the  value  of  the  meadows  found  frequently  by  the  side  of  such 
streams  is  due  entirely  to  the  moisture  obtained  from  the  water 
thus  held  up.  There  are  many  light  soils,  notably  the  black 
peat  lands  and  the  lands  in  Holland,  which  are  only  rendered 
fit  for  cultivation  by  means  of  the  water  which  is  held  up  in 
the  drains  which  intersect  the  district.  This  keeps  the  under- 
stratum of  the  soil  sufficiently  moist  in  hot  weather  to  feed  the 
growing  plants.  For  purposes  of  irrigation,  also,  water  requires 
to  be  maintained  at  a uniform  level  in  the  river  channels.  The 
value  of  vr~_  :r  for  this  purpose  is  hardly  sufficiently  recognized 
YOL.  XIX. — S.  S.  * 2 E 
