Environmental Engineering Reference
In-Depth Information
contour lines of equal depth (depth contours or isobaths), or digital elevation
models showing bathymetry in shaded relief. Historically, bathymetric maps were
used for navigation (i.e., to prevent ships from running aground), but as field
biology and environmental sciences have developed, bathymetric mapping has
been applied to address a range of hydrologic and ecological questions in wetlands.
Wetland bathymetric maps have many applications, including determining water
storage capacity and hydroperiod (depth and timing of flooding), assisting with
wetland design and restoration and land use planning, and facilitating legal bound-
ary determination.
Hydrologic conditions in wetlands were typically monitored by determining
wetland water level at a fixed point near the deepest part of a wetland. However,
water level alone tells us very little about the distribution or evolution of hydrologic
conditions in a wetland, and how these conditions influence physical, chemical, and
biological characteristics. The usefulness of long-term data sets of wetland water
levels would greatly increase if the data described not only the depth of water at a
point in the wetland, but also the amount of total wetland areas that was inundated
at a specific time (Haag et al.
2010
). A survey of wetland bathymetry and the
surrounding topography can help us understand how water moves through the
landscape, and more specifically, how water influences the hydrologic budget of
the wetland. The water budget of a wetland depends on the input and output of
water where the storage capacity of the wetland and bathymetry determines storage.
In addition, wetland bathymetry will influence residence time, flood retention,
sediment trapping (Gallardo
2003
; Takekawa et al.
2010
), and regional surface
and ground water interactions (Poole et al.
2006
). Bathymetry plays a key role in
plant and animal community dynamics (van der Valk
1981
; Ripley et al.
2004
) and
wetland biogeochemistry (Faulkner and Patrick
1992
). For example, the depth of
the water and hydroperiod can control the presence-absence of taxa (van der Valk
1981
; Bliss and Zedler
1997
) and their interactions (Pechmann et al.
1989
; Corti
et al.
1997
; Karraker and Gibbs
2009
). In particular, the depth of the water may
control vegetation dynamics, such as the establishment and growth of various
emergent or floating plant species (van der Valk
1981
; Keeley and Sandquist
1992
). In summary, with adequate bathymetric maps, we can develop a description
of the dynamic changes in wetland conditions instead of a simple snapshot
(Takekawa et al.
2010
). Moreover, we can translate periodic and widely distributed
water-level measurements into a regional view of wetland hydrologic status
(Lee et al.
2009
).
This chapter introduces several survey strategies and methods for measuring
wetland bathymetry, and discusses their attributes and limitations. An overview of
the use of geographic information system (GIS) is also provided to assist students
with an understanding of how to analyze typical bathymetric measurements
(Fig.
2.1
). Finally, we include an exercise at the end of the chapter that uses a
pre-existing survey data set to provide students with experience in using GIS to
analyze bathymetry measurements of a wetland.
