730 IOWA DEPARTMENT OF AGRICULTURE 
more than one day, even where it originally fell, it injures farm crops; 
for that reason we may add: Get it down immediately. It will do but 
iiitle good to get it down unless a way is provided by which it may 
flow away. This way must have slope enough to cause the water to flow, 
and be large enough to hold the volume of water to be moved and at the 
same time keep it at a safe depth below the surface of the soil. The 
volume of water to be moved, and the slope of the waterway, or drain, 
as we call it, are usually items which are fixed by nature and both affect 
the required size. So we cannot judge of the required size unless we 
know the slope and the volume. Then here is another rule: Ascertain 
the available slope of the drain and the volume of water to he moved. 
When the drain is constructed if there are^ places where the slope is 
greater than at others the water will flow more rapidly at those places, 
but the water will not get away any more rapidly than it flows at the 
flatest place, and so we should make the drain of uniform slope if pos- 
siole. It is true also that crooks and bends in a drain obstruct the flow, 
and a drain should be made in as straight a line as possible. 
Open drains when constructed often become obstructed by flowing silt, 
falling turf and growing vegetation, and besides they are a serious an- 
noyance in cultivating land and destroy a considerable portion of land 
that should raise good crop with less labor in farming. Where it is 
possible to use covered drains, they are less liable to obstruction, the 
land is saved from loss and waste, and good crop is grown where with an 
open drain there is nothing but an unsightly hole with weeds on its 
banks. Then let us make the rule: Always use a covered drain if 
possible. 
Nature has wisely prepared the surface of the earth so that in most 
places there are plane of more or less spherical surfaces with natural 
slope in some direction. These sloping surfaces intersect each other in 
all manner of ways, but the intersections of the lower edges make con- 
tinuous water courses toward some river or natural body of water. These 
natural courses are liable to become overflowed, because the water natur- 
ally seeks them. Water will not cross these courses to seek a drain 
somewhere on the surface sloping to it. For that reason it is needful to 
locate drains near the natural water course and these of necessity are 
often crooked and meandering, but there is no reason why the drains 
on the sloping surfaces should not be in straight lines, parallel with each 
other, and it is much better to have them so as it gives uniform results 
and systematic work. Then we would say: Locate the main drains 
along tne natural water courses, but make the lateral drains as near cw 
possible parallel with each other, even though you disregard slight un- 
dulations of the land. Lay them out so they will follow the line of 
greatest fall, only modified to a reasonable extent to keep the lines 
parallel and avoid acute angles at the junction. 
The law of this country gives every man a right to have the water 
flow from his land onto the land of his neighbor in its natural course, in 
natural quantity on the surface of the ground or in a natural channel. 
This is a wise and just law, but often the outlet thus afforded is not deep 
enough to give perfect drainage. Thus it is often necessary to co-operate 
with neighbors to get good results. This is not always possible, and our 
