EXERCISE 1
Lake Basin Characteristics
and Morphometry
Limnological analyses of a lake or stream very
often require a detailed knowledge of morphometry, particularly of the volume characteristics of the body of fresh water. Depth analyses,
including measurement of areas of sediments and
of water strata at various depths, volumes of
strata, and shoreline characteristics, are often
critical to detailed analyses of biological, chemical, and physical properties of fresh waters.
Morphometric parameters are needed for
example, to evaluate erosion, nutrient loading
rates, chemical mass, heat content and thermal
stability, biological productivity and effectiveness of growth, and many other structural and
functional components of the ecosystem. Management techniques, such as the loading capacity
for effluents and the selective removal of un desirable components of the biota, are also heavily
dependent on a detailed knowledge of the morphometry and water retention times in freshwater ecosystems.
Accurate hydrographic maps of lakes and
streams are rarely available in sufficient detail for
the limnologist. It is a characteristic feature that
the morphometry of lakes and streams changes
with time, so even if bathymetric (i.e., depth
contour) maps are available from governmental
or other sources, their accuracy should be
checked carefully. It is essential, therefore, that
the rudiments of the construction of bathymetric
maps and the computation of morphometric
parameters be understood.
LOCATION WITHIN PROJECTIONS: GEOGRAPHICAL COORDINATES
Latitude, Longitude, and Bearings
A level surface, such as the surface of a lake, is parallel everywhere to the mean surface of
the earth and so is essentially spherical. A level line is the arc of a circle whose radius
varies according to the elevation above or below mean sea level. In the survey of small
areas, or when sight lines are short, level surfaces are assumed to be planes, and level
lines are assumed to be straight lines.
A great circle is the trace of a level line on a vertical plane and may be illustrated by
imagining a vertical plane passing through the polar axis of the earth. The trace of the
earth's surface on this vertical plane is considered to be a great circle.
Geographic meridians and parallels oflatitude are a system of spherical coordinates
by which it is possible to locate points or to describe precisely the locations of points on
the surface of the earth. Geographic meridians (longitudes) are of great circles, since
1
Lake Basin Characteristics
and Morphometry
Limnological analyses of a lake or stream very
often require a detailed knowledge of morphometry, particularly of the volume characteristics of the body of fresh water. Depth analyses,
including measurement of areas of sediments and
of water strata at various depths, volumes of
strata, and shoreline characteristics, are often
critical to detailed analyses of biological, chemical, and physical properties of fresh waters.
Morphometric parameters are needed for
example, to evaluate erosion, nutrient loading
rates, chemical mass, heat content and thermal
stability, biological productivity and effectiveness of growth, and many other structural and
functional components of the ecosystem. Management techniques, such as the loading capacity
for effluents and the selective removal of un desirable components of the biota, are also heavily
dependent on a detailed knowledge of the morphometry and water retention times in freshwater ecosystems.
Accurate hydrographic maps of lakes and
streams are rarely available in sufficient detail for
the limnologist. It is a characteristic feature that
the morphometry of lakes and streams changes
with time, so even if bathymetric (i.e., depth
contour) maps are available from governmental
or other sources, their accuracy should be
checked carefully. It is essential, therefore, that
the rudiments of the construction of bathymetric
maps and the computation of morphometric
parameters be understood.
LOCATION WITHIN PROJECTIONS: GEOGRAPHICAL COORDINATES
Latitude, Longitude, and Bearings
A level surface, such as the surface of a lake, is parallel everywhere to the mean surface of
the earth and so is essentially spherical. A level line is the arc of a circle whose radius
varies according to the elevation above or below mean sea level. In the survey of small
areas, or when sight lines are short, level surfaces are assumed to be planes, and level
lines are assumed to be straight lines.
A great circle is the trace of a level line on a vertical plane and may be illustrated by
imagining a vertical plane passing through the polar axis of the earth. The trace of the
earth's surface on this vertical plane is considered to be a great circle.
Geographic meridians and parallels oflatitude are a system of spherical coordinates
by which it is possible to locate points or to describe precisely the locations of points on
the surface of the earth. Geographic meridians (longitudes) are of great circles, since
1