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Background
The Water Quality Act of 1987, in Section (314), the Clean Lakes Section and
Section 305(b) mandates the development of a public lakes assessment program. The
primary objectives of the Lakes assessments were to:
- Identify lakes which were not currently meeting water quality standards;
- Identify degraded, impaired, or threatened lakes; and
- Identify the trophic status of each of these lakes.
Sampling Methodology
All sampling was conducted in mid to late summer after significant
run-off had ceased and summer stratification had occurred on most lakes. Each sampling
trip was restricted to no more than two days so the samples could be analyzed within
the 48-hour maximum holding time. The Environmental Preservation and Technical Services
Division of the Department of Environmental Quality analyzed water quality parameters.
The Water Quality Planning Branch of ADEQ collected samples, measured dissolved
oxygen profiles, pH and secchi transparency (visibility into water) in the field.
A shore to shore transect in the lower portion near the dam of
each man-made lake was established; depths along transects were determined; and
a sample station was established at the deepest point. Lakes of approximately 2000
surface acres or larger had more than one sample transect. These included one near
the dam and one in the upper one-third of the lake. Naturally occurring lakes were
sampled at their deepest point, which was normally near the middle of the lake.
Water temperature and dissolved oxygen concentrations were measured
at 1 to 5 feet intervals within the epilimnion (upper strata); at 1 to 2 feet intervals
in the thermocline (transition zone); and 1 to 5 feet intervals in the hypolimnion
(lower strata).
Water quality grab samples were collected at one meter (epilimnion)
and at 0.8 (80%) maximum depth (hypolimnion) over the main channel. Bacteria samples
were collected one-half meter below the surface at five locations along the transect.
One sample was collected approximately 50 feet from each shore, at each quarter
point and at the mid-point of the transect. Chlorophyll a samples were
collected from the five bacteria sample sites along the transect and composited.
Lakes Classification
Using size, average depth and ecoregion all lakes were placed into
one of five different lake types.
Type A Lakes
- These are the larger lakes, usually of several thousand acres
in size. They have average depths normally 30 to 60 feet. They are located in
the montane areas of the state in the Ozark Highlands, Ouachita Mountains and
Boston Mountains. The primary purposes for construction of these lakes was hydropower
and/or flood control. The watershed to lake area ratios (W/A) are normally large,
but most of these lakes have large storage volumes and a relatively long hydraulic
residence time.
Type B Lakes
- These include the smaller lakes of the uplands or steeper terrain.
Most are around 500 acres or less in size, but probably are the most heterogenous
group of lakes. Most are located in the Ozark Highlands, Ouachita Mountains
and Boston Mountains; however, several are located in the more mountainous areas
of the Arkansas River Valley. Average depths are relatively deep and range generally
from 10 to 25 feet. Watersheds are normally dominated by forest lands. Most
lakes of this type were constructed for the primary purpose of multi-purpose
recreation or specifically for public fishing. The watershed to lake area ratios
are generally very large. This results in a rather high flushing rate and low
water retention time.
Type C Lakes
- This group is composed of the smaller lakes of the lowland
or flat terrain areas. Sizes generally range from 300 to 1,000 acres with average
depth of normally less than 10 feet. These lakes are located in the flatter
terrain of the Arkansas River Valley, Gulf Coastal and Delta Ecoregions. The
Delta lakes of this group are generally associated with the Crowley's Ridge
region. Watersheds of these lakes include timberlands of both lowland hardwoods
and pines, but some are broken by pasture land and small farms. Almost all lakes
of this group were constructed specifically for public fishing with other types
of recreation as secondary uses. The watershed to lake area ratios vary significantly.
As a result of the shallow average depth and relatively small storage volume,
high flushing takes place on the lakes that have high W/A ratios.
Type D Lakes
- These are small impoundments of the Delta area of the state,
but include two similar type lakes from the large river alluvium of the Gulf
Coastal Ecoregion. These type lakes are generally 200 to 500 acres in size with
average depths of five feet. This group includes several natural, oxbow-cutoff
lakes which have been modified by a water control structure to increase their
isolation form the parent stream and maintain higher dry-season water levels.
These lakes are only occasionally flooded by the parent stream and generally
have very small direct runoff watersheds. Other lakes of this type are man-made,
but they are almost totally isolated from their watershed by levees. Water levels
are maintained through occasional pumping from adjacent waterways. Where watersheds
exist that discharge directly to the oxbow lakes in this group, the runoff is
primarily from row crop agriculture.
Type E Lakes
- These are the large lowland lakes of the Delta, Gulf Coastal
and the large alluvial areas of the Arkansas River Valley Ecoregion. They range
from several thousand to over 30,000 acres in size, but average depth is usually
less than 10 feet. This group also includes four large, oxbow-cutoff lakes which
have been substantially modified by construction of drainage ditches, levees
and other water control structures. Watershed types include mixtures of intensive
row crop agriculture, small farms and pastures. The range of watershed to lake
area ratios within this type of lake is extremely large. The largest is on navigation
impoundments on the main stream of the large rivers. The flood control reservoirs,
as might be expected, also have relatively large W/A ratios. In contrast the
large oxbow lakes have W/A ratios of usually less than 10.
Water Quality Data
Summary information and a location map can be found in the document Arkansas' Significant Publicly-owned Lakes.
The following table has links to detailed information for each of the significant
publicly-owned lakes.
