TM 5-820-3/AFM 88-5, Chap. 3
more or less uniformly along its length. The depth
of flow and the velocity head increase downslope in
Shallow, structurally adequate paved gutters adja-
the gutter, and the slope of the energy gradient is
cent to airfield pavements are frequently required
therefore flatter than the slope of the gutter. The
to provide positive removal of runoff from paved
error increases rapidly as the gutter slope is
areas, to protect easily eroded soils adjacent to the
flattened, and on very flat slopes the gutter capacity
pavement, and to prevent the softening of turf-
is much less than that computed using the gutter
shoulder areas caused by the large volume of runoff
slope in Manning's equation.
from adjoining pavements.
4-3. Design charts.
4-2. Discharge capacity.
A cross section of a typical runway gutter and the
The discharge capacity of gutters depends on their
design charts are shown in figure 4-1. Safety and
shape, slope, and roughness. Manning's equation
operational requirements for fast-landing speeds
may be used for calculating the flow in gutters;
make it desirable to provide a continuous longitu-
however, the roughness coefficient n must be
dinal grade in the gutter conforming closely to the
modified somewhat to account for the effect of lat-
runway gradient thereby minimizing the use of
eral inflow from the runway. The net result is that
sumped inlets. A sufficient number of inlets will be
the roughness coefficient for the gutter is slightly
provided in the gutter to prevent the depth of flow
higher than that for a normal surface of the same
from exceeding about 21/2 inches.
type. The assumption of uniform flow in gutters is
not strictly correct since runoff enters the gutter