18 BULLETIN L207, U. s. DEPARTMENT OF AGRICULTURE. 
of water to be carried, on the fall and on the kind of drain it is 
advisable to construct. The disadvantage thus varies with eacli 
tract and. therefore, must be separately determined. In many dis- 
tricts this disadvantage is measured by the distance of the land 
from the drain, eliminating other factors, though they are in many 
cases fully as important. Allowance for this disadvantage in terms 
of the cost of the district drain, as is often made, is incorrect, since 
the disadvantage is in no way affected by the cost of the district 
improvement. 
It is not always possible to obtain a sufficient outlet for a drainage 
system, so that the quality of the outlet becomes an important factor 
in estimating the benefits. Usually only land near the lower end 
of the district is affected by a poor outlet, and as the engineer can 
estimate the extent and frequency of flooding, a corresponding re- 
duction should be made in the benefit of the a fleeted land. 
The matter of health as a special benefit is too often neglected, 
for although such benefits may be general to the community, they 
are also special benefits to those who live in the immediate vicinity 
of the improvement. 
The factor of increased accessibility applies to lands rendered 
more easy of access by the drainage of adjacent wet lands. Such 
lands need not be entirely surrounded by swamps; a common ex- 
ample of such a benefit is that which ensues from the drainage of 
a swale or wet ground which previously has separated one part of 
a farm from another. 
Property should be assessed according to use which is made of it. 
or to which it is reasonably adapted. The benefits due to drainage 
are different in kind and amount for agricultural lands and for 
lands used for highways, railroads, residence or factory sites. The 
drainage benefits to be considered are those which will result when 
the land shall be used for that purpose for which it is most valuable. 
There are other factors which might be included in the above list, 
but their application is not general enough to warrant inclusion in 
a general statement. Many of these are correctly used at times and 
under other conditions should be omitted. One such factor is soil 
fertility. This should be used with great care: the prevailing ten- 
dency is to give it too much weight. Rich, undrained land has a 
greater value than poor, undrained land. The greater return made 
by rich lands when drained is due the owner for his more valuable 
property, and is not due to drainage improvement. This factor 
should be omitted from consideration except where it is considered 
as affecting both the drained and undrained value of the land, but 
where costs of the work are apportioned according to an arbitrary 
scale it should probably be used, since some soils which are of little 
worth either before or after drainage might be assessed too heavily 
were this factor omitted. 
The drainage properties of soils should be considered whenever 
there is marked variation in these qualities throughout the district. 
The width of the strip of land drained by a ditch or tile drain de- 
pends largely on the porosity of the soil. When a drain crosses a 
tract having porous soil the land on each side of the drain will be 
completely drained possibly for one or two hundred feet. On an- 
other tract with impervious soil the land may not be drained more 
than a few feet back from the drain. It might appear that the bene- 
