592 Jt/h Mann’s f treatije 
generally the cafe in Holland and Flanders, all depth of 
the bed of the canal below the horizontal level of the 
bottom of the fluice will ferve to no manner of purpofe, 
either for navigation, or for carrying off the back-waters, 
but will foon fill up with mud, in fpite of all means ufed 
to the contrary, except that of digging it continually 
anew to no manner of purpofe ; as is evident from the 
reafons given above (N° 3.3. 34.). 
38. Setting off from this determinate point, at the 
mouth of a river, or at the bottom of the laft fluice upon 
a canal, which are to be cleaned and deepened ; the work 
muff be carried on, in confequence, uniformly through- 
out their whole courfe backwards into the country as far 
as is found neceffary for the purpofes intended. This is 
to be done after the following manner : 
iff, One mull dig up and carry away all irregularities 
in the bottom and fides of the bed, fuch as banks of fand 
and mud, rocks, flumps or trunks of trees, and whatever 
elfe may caufe an obftacle to the regular motion of the 
water, and to the free paffage of veffels upon it. 
izdly, If the declivity of the bed fhould be ftill too 
little to give a fufficient current to carry off the water as 
often and as fall as is neceffary, the whole bed itfelf muff be 
regularly deepened, and what is dug out from the bot- 
tom muff be laid upon the fides, to render it narrower in 
proportion 
