Soil
Geomorphology
Understanding slopes, landscapes
Understanding slopes, landscapes
and landforms
NDWRCDP Disclaimer
This work was supported by the National Decentralized Water
Resources Capacity Development Project (NDWRCDP) with
funding provided by the U.S. Environmental Protection Agency
through a Cooperative Agreement (EPA No. CR827881-01-0)
with Washington University in St. Louis. These materials have
not been reviewed by the U.S. Environmental Protection
Agency. These materials have been reviewed by
representatives of the NDWRCDP. The contents
of these materials do not necessarily reflect the views and
policies of the NDWRCDP, Washington University, or the U.S.
Environmental Protection Agency, nor does the mention of trade
names or commercial products constitute their endorsement or
recommendation for use.
CIDWT/University Disclaimer
These materials are the collective effort of individuals from
academic, regulatory, and private sectors of the
onsite/decentralized wastewater industry. These materials have
been peer-reviewed and represent the current state of
knowledge/science in this field. They were developed through a
series of writing and review meetings with the goal of
formulating a consensus on the materials presented. These
materials do not necessarily reflect the views and policies of
North Carolina State University, and/or the Consortium of
Institutes for Decentralized Wastewater Treatment (CIDWT).
The mention of trade names or commercial products does not
constitute an endorsement or recommendation for use from
these individuals or entities, nor does it constitute criticism for
similar ones not mentioned.
Citation
Lindbo, D.L., M. Stolt, R. Miles, and D.
Mokma. 2005. 2. Soil Geomorphology –
Power Point Presentation. in (D.L. Lindbo
and N. E. Deal eds.) Model Decentralized
Wastewater Practitioner Curriculum.
National Decentralized Water Resources
Capacity Development Project. North
Carolina State University, Raleigh, NC.
Soil Geomorphology
¾Slopes and water movement
¾Topography
Slopes
Slopes
¾ Position
¾ Hydrologic cycle
¾ Slope considerations
¾ Drainage
Slope Position Names
Side or back slope
Summit
Shoulder
Foot slope
Toe slope
Hydrologic Cycle
Septic System
Precipitation
Infiltration
Evapotranspiration
Wastewater
Input
Water Table
Lat
Runoff
era
Slo
l
Flo
wly
w
Per
mea
ble
laye
r
Stream
Ground Water
Slow Moving
Impermeable Layer
HYDROLOGY OF A SEPTIC SYSTEM
Infiltration from
Trenches
Vertical Movement
through the
Unsaturated Zone
Lateral Movement
in the Saturated Zone
Least Permeable
Ground Water Mounding and
Formation of a Saturated Zone
Slowly Permeable Layer
How does slope influence the hydrology of
a septic system?
SCHEMATIC CROSS SECTIONAL AREA OF A DRAINFIELD
Back Fill
Soil Surface
Pipe
Gravel
Ap
Bt1
Bt2
BC
C
R
DRAINFIELD
Drainage on a sloping lot
WT
Curtain Drain
WT
Outlet
A proper outlet must.
• be clear and free
flowing.
• exit topographically
below the bottom of
the deepest trench
Does this site look good?
Or is a curtain drain needed?
Drainfield and
Lot
Configuration
Slope Considerations
1
2
Horizontal Flow
3
Contour Lines
Drainage
Drainfield
Direction of Ground water Flow
Contour Lines
Drainage
Drainfield
Direction of Ground water Flow
Dra
in
fiel
d
Drainage
Direction of Ground water Flow
Topography
Soils on slope
Up Slope
Down Slope
Topography
¾ Dissected regions
¾ Broad, flat regions
Dissected Regions
¾ Well-drained soils at summit
¾ Poorly-drained soils in low areas
W
r
D
ell
U
d
e
ain
WATER TABLE
d
n
pla
D
y
rl
o
Po
d
e
n
i
ra
Well drained at summit
Poorly drained in low area
Broad, Flat Regions
¾ Large distances between streams
(interstream divides)
¾ Poorly-drained soils may be at high points
on landscape
¾ Well drained soils closest to drainage (dry
edge effect)
D
y
rl
o
Po
d
e
n
i
ra
W
W
ell
D
l
l
e
Dr
d
e
ain
r
D
–
e
g
d
E
y
D
y
rl
o
Po
d
e
n
i
ra
r
D
–
d
e
n
i
a
r
e
g
d
E
y
Dry Edge Effect
Channel
Dry edge
Poorly
drained
Typical wet flat area; drainage
needed for agriculture etc.
What is going on at this site?