Agriculture Reference
In-Depth Information
site to the culvert. The culvert is a large-diameter pipe installed under
an entrance driveway. The water from the swale is carried downstream
through the culvert to the swale that continues on the other side of the
access road. The swale is sloping at 2 percent (a 2-foot drop in elevation
for every 100 feet of horizontal length). The lines drawn on the image
represent contours and where they would fall if they actually existed.
Without the photograph, the shape of the contours would be a graphic
means to visualize the same landscape in plan, in this case the adjacent
slope and swale that carry the water to the culvert entrance.
contourS uSed to ShoW Surface drainaGe
First, through the activity of site grading, we can transform an existing
site's landform to accommodate specific program elements. Another
important goal of site grading is to make sure surface water flow across
the site landscape avoids flooding and ponding where it is not wanted—
for example, the ponding in an entry drive and parking lot shown in
Figure 11.11. This ponding could have been avoided by forming the
ground surface to direct surface water flow to another location, such as
a drainage swale, catch basin system, detention pond, or bioswale. There
is a reasonable chance that when the original grading and construction
of the area shown in Figure 11.11 were done, they were done correctly.
However, the resurfacing of the neighborhood road or some other main-
tenance operation may have caused a blockage, allowing water to pond
with no way to exit to the adjacent drainage swales. Another possibility
is that ground subsidence may have occurred, creating a pond-like sur-
face where surface water could collect.
Seemingly paved surfaces such as parking lots and plazas appear
level but almost always are sloped, either in one direction as a mono-
lithic whole, or, more often, as a series of watersheds with water
directed as low as 1 percent to a catch basin, drainage swale, or drain-
age system. Catch basins are commonly employed to receive surface
water, as in the parking lot shown in Figure 11.12. The photograph was
taken several hours after a rain. From the picture you can easily see the
pavement is sloping and how the water is directed to the receiving catch
