FOURTH on the Keyline scale of the relative permanence of thingsagricultural is farm roads. The main farm roads are influenced in their locationby the climate and the land shape, since our study of the patterns of water movementover various land shapes provides a basis for determining the sites of the roads.Increasing volumes of flow water are hazards to roads, so that their trafficabilityin wet weather and their cost in maintenance are vitally affected. The centre ofmain ridges, which form part of the boundaries of the secondary valleys, are neutrallines of no flow, and being high and dry are very suitable sites for main roads.
The influence of the water conservation drains of Keyline andthe position of irrigation drains and irrigation areas determine the sites and generalpatterns for work roads and are arranged as follows: Those roads which run acrossthe land follow the water conservation drain either above or below it; others whichfollow the irrigation drain are located above it so that irrigation water will notflow across the road. Again, other roads may follow the lower boundary of an irrigationarea and another road on either side of the breaks of the land, namely the watercourses.
Some of these considerations have always influenced the sitingof farm roads, but the relationships of the factors of the Keyline scale of permanenceand the appreciation of the new significance agriculturally of land shape providesa guide so positive that all road sites are selected to advantage because all factorsin their siting are understood. Farm roads, while serving their purpose, change thenatural drainage pattern either towards destruction or preservation of land profiles.From the general planning of Keyline it will be seen that the position or sites offarm roads become natural, obvious, and constructive.