Hydrologic discharge control assembly and method

A hydrologic discharge control assembly and method is disclosed for automatically withdrawing bottom water from a body of water comprising a housing for forming a reservoir to receive bottom water for automatic gravitational discharge relative to the height of the top surface of the body of water, the reservoir having a discharge overflow edge portion adapted for operational connection to the discharge drain passageway of the body of water and being disposed for overflow discharge of water within the reservoir in excess of a predetermined level, and an inlet connector fluidly connecting the housing to the bottom water portion of the body of water and being dimensioned and configured relative to the housing for conduction of bottom water into the reservoir relative to the height of the top surface of the body of water.

BACKGROUND AND SUMMARY OF THE PRESENT INVENTION 
This invention relates to the hydrologic control of lakes and ponds and 
more particularly to an apparatus and method for automatically controlled 
withdrawal of bottom water for controlling the growth of aquatic weeds and 
algae. 
Lakes, ponds and other impoundments are frequently polluted by an excess 
growth of aquatic macrophytes, algae, and other microorganisms which 
create unacceptable water quality conditions for recreation, water supply, 
and wild life habitat during the growing season. As surface water becomes 
warm during the spring, the bottom water of a water body, such as a lake, 
becomes isolated from atmospheric gas exchange due to the differences in 
water density at different water temperatures. The desnity layers formed 
in the lake therefore result in different water quality between the 
surface water and the bottom water. 
As organic materials decompose at the bottom of the lake, oxygen is 
consumed and carbon dioxide and nutrients are generated and released. The 
decomposition process results in the release of large amounts of 
phosphorus, nitrogen, carbon dioxide and other substances from the 
nutrient-rich sediments at the bottom of the lake and, during the growing 
season, the nutrients generated from the lake bottom contribute to the 
excessive growth of macrophytes and algae and the attendant unacceptable 
water conditions. 
It is an object of the present invention to provide an apparatus and method 
for controlling aquatic macrophyte and algae growth by altering the 
outflow configuration of the water body for controlled discharge of bottom 
water as well as surface water. 
Another object of the invention is to provide an apparatus and method for 
removing dense cool oxygen-deficient nutrient-rich bottom water from a 
water body at a rate which automatically adjusts to varying hydrologic 
conditions. 
A further object of the invention is to provide an improved hydrologic 
discharge control assembly for the automatic withdrawal of bottom water 
without the need for pumping, siphoning, frequent adjustments, or large 
fluctuations in water level. 
Yet another object of the invention is to provide a hydrologic discharge 
control assembly which achieves automatic bottom water withdrawal, 
adjustable surface-bottom water outflow ratios, and adequate flood storage 
while minimizing water body level fluctuations. 
Other objects will be in part obvious and in part pointed out in detail 
hereinafter.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings in detail wherein like numerals are used to 
designate the same or like parts, the hydrologic discharge control 
assembly of the present invention is generally designated by the numeral 
10 and is shown in FIG. 1 operationally mounted within a landlocked water 
body or lake 12 with epilimnion, metalimnion and hypolimnion layers. The 
lake 12 is of the type adapted for lake-level control by a spillway system 
and has an outlet stream or discharge drain passageway 14 and an elevated 
side edge 16 adapted to support a flashboard system adjacent the outlet 
stream. 
The discharge control assembly 10 includes a flashboard box 18 connected by 
a conduit 20 to a bottom water collector 22. The flashboard box 18 has 
opposing side walls 24, a bottom wall 26, a forward wall 28, and a 
rearward wall 30 together forming an interior reservoir or receptacle 32. 
The forward wall 28 has an inlet port 34 connected to the bottom water 
conduit 20 to receive bottom water into the reservoir 32. The forward wall 
28 also has a vertically extending inlet slot 36 for receiving surface 
water into the reservoir 32. An inlet flashboard wall assembly 38 controls 
the inflow of surface water through the slot 36 and includes a plurality 
of interlocking flashboard elements 39 detachably mountable within the 
inlet slot 36 for selective gradational closing off of the inlet slot 36 
to control the inflow of surface water relative to the height of the lake 
and the height of the inlet wall assembly 38. Each flashboard element 39 
is configured to slidably mount within the slot 36 and sealingly interlock 
with the forward wall 28 and adjacent upper and lower flashboard elements 
39. 
The rearward wall 30 has a vertically extending outlet slot 40 for 
discharging water out of the receptacle area 32. A discharge flashboard 
wall assembly 42 controls the discharge of water through the slot 40 and 
is comprised of a plurality of interlocking flashboard elements 44 
detachably mountable within the discharge slot 40 for selective 
gradational closing off of the discharge slot 40 to control the discharge 
of water relative to the height of the water within the flashboard box 18 
and the height of the discharge wall assembly 42. Each flashboard element 
44 is configured to slidably mount within the slot 40 and sealingly 
interlock with the rearward wall 30 and adjacent upper and lower 
flashboard elements 44. 
The flashboard box 18 is supported atop the elevated side 16 of the lake 12 
so that the inlet slot 36 adjoins the body of water and the discharge slot 
40 is positioned adjacent the discharge drain 14 so that water spilling 
outwardly through the discharge slot 40 and over the discharge flashboard 
wall assembly 42 flows into the drain 14. 
Bottom water is received into the reservoir 32 through the conduit 20 and 
the bottom water collector 22. The bottom water collector 22 comprises a 
housing 46 having opposed inclined side walls 48, an inlet opening 50, and 
an opposed outlet port 52 connected to the conduit 20. The inlet opening 
50 is dimensioned and configured to control the inflow velocity of bottom 
water into the collector 46 and is covered by a screen element 54. In 
water bodies which form an epilimnion, metalimnion and hypolimnion, such 
as the lake 12 illustrated in FIG. 1, it is preferred that the screened 
opening 50 be dimensioned and configured sufficiently to reduce the inflow 
velocity below 0.5 feet per second. 
In shallow bodies of water which do not form a distinct epilimnion, 
metalimnion, hypolimnion, an alternate bottom water collector is preferred 
in order to distribute the withdrawal effects over a large bottom area of 
the water body. The alternate bottom water collector 56 comprises an 
elongated section of pipe 58 having a plurality of perforations or 
apertures 60 therein. Generally, the total area of the apertures should be 
sufficient to reduce the inflow velocity to less than 0.1 feet per second. 
In operation, the discharge flashboard wall assembly 42 is assembled with a 
selected number of flashboard elements 44 so that the upper edge 45 of the 
uppermost flashboard element 44' forms a discharge overflow edge to define 
a predetermined spill-over level for the flashboard box. Similarly, the 
inlet flashboard wall assembly 38 is assembled with a selected number of 
flashboard elements 39 assembled to provide a predetermined inlet 
spill-over level as defined by the upper inlet overflow edge 37 of the 
uppermost flashboard element 39' of the inlet flashboard wall assembly 38. 
Both the predetermined discharge spill-over level 45 and the predetermined 
inlet spill-over level 37 are selectably variable by varying the 
respective heights of the discharge flashboard wall assembly 42 and the 
inlet flashboard wall assembly 38. 
The pipe diameter of the conduit 20 is dimensioned for each individual body 
of water according to system hydrology, basin morphometry, rates of 
decomposition and nutrient release, and total available head. In general, 
the pipe diameter is of a size to accommodate the mean annual outflow from 
the particular body of water. The predetermined inlet spill-over level of 
the inlet flashboard wall assembly is always maintained at a level higher 
(or equal to) the predetermined discharge spill-over level of the 
discharge flashboard wall assembly, During summer operation, both levels 
are maintained at a higher elevation than during winter, spring, and fall 
operation in order to maintain a full body of water for the summer and 
allow for greater flood-water storage and flushing rate during fall, 
winter, and spring. 
The withdrawal of bottom water from the lake into the flashboard box 18 for 
discharge is controlled by the effective head of the control assembly 10. 
The effective head H is determined by the vertical differential of the top 
surface of the lake 12 and the predetermined discharge spill-over level 45 
of the discharge flashboard wall assembly 42. The effective head H 
increases automatically as the lake level rises and correspondingly causes 
the withdrawal of bottom water to increase automatically as the lake level 
rises. Consequently, a greater withdrawal rate is accomplished when 
additional water is available. The discharge of bottom water is a function 
of the length of the discharge overflow edge 45 and the depth of the water 
over said edge. The vertical differential d between the preset inlet 
overflow edge 37 and the discharge overflow edge 45 establishes the 
maximum bottom withdrawal rate relative to total outflow. 
Referring to FIG. 5, when storm water inflow exceeds outflow over the 
discharge overflow edge 45 at a depth exceeding d, surface water will 
spill over the upper inlet overflow edge 37 of the inlet flashboard wall 
assembly into the flashboard box 18 for discharge with the bottom water. 
Selective variation of the relative levels of the discharge flashboard 
wall assembly and the inlet flashboard wall assembly permits variation of 
the ratio of bottom water and surface water discharged from the flashboard 
box 18. Selective variation of the relative levels and withdrawal ratios 
can be further enhanced by incorporating a v-notch spillway 43 in the 
uppermost flashboard element 41 of the inlet flashboard wall assembly 38. 
By setting the bottom of the v-notch 43 at the elevation of the upper edge 
45 of the discharge wall assembly 42 as shown in FIG. 6, some surface 
water will always be part of the total discharge. 
As can be seen, the discharge control assembly 10 provides automatic 
gravitational discharge of bottom water relative to the height of the 
surface of the lake and automatically removes bottom water at a varying 
rate which depends upon the spill-over levels of the discharge and inlet 
flashboard wall assemblies and the hydrologic conditions of the lake 12. 
Additionally, only infrequent manual adjustments are required to account 
for changes in the seasons, withdrawal rate is maximized for varying 
hydrologic conditions, and the lake level fluctuates only slightly. 
Through the automatic controlled removal of bottom water, the growth of 
aquatic weeds and algae is controlled and the quality of water is 
improved. The removal of nutrient-rich bottom water not only removes a 
source of nutrients for the aquatic weeds and algae growth but results in 
a retardation of nutrient release from the bottom sediment and avoids the 
consequences of an anoxic bottom layer. The removal of oxygen-deficient 
bottom water causes the more oxygen-laden water from the upper levels to 
move downwardly. The presence of oxygen retards the release of nutrients 
as, for example, phosphorus from the bottom sediment. Accordingly, plant 
growth is controlled and the quality of water is improved. 
Referring to FIG. 7, an alternate embodiment of the discharge control 
assembly of the present invention is shown and generally designated by the 
numeral 62. The control assembly 62 is adapted for utilization with a 
water body or lake 13 of the type having a deep subsurface outlet culvert 
64 which extends laterally through the side edge 16 of the lake to connect 
the lake to the discharge drain 14. 
The discharge control assembly 62 comprises an inner conduit 66 coaxially 
vertically disposed within an outer conduit 68 to form a reservoir space 
or receptacle 70 therebetween. 
The outer conduit 68 has an inlet port 72 at its lower end connected to the 
bottom water conduit 20. The upper end 74 of the outer conduit 68 is open 
with a circumferential edge 76 providing a predetermined inlet spill-over 
level (similar to the inlet spill-over level 37 of the embodiment of FIG. 
4) so that surface water of the lake above the predetermined inlet 
spill-over level 76 overflows into the outer conduit 68. 
The inner conduit 66 is connected at its lower end to the outlet culvert 
64. The upper end 78 of the inner conduit is open with a circumferential 
edge 80 providing a predetermined discharge spill-over level (similar to 
the discharge spill-over level 45 of the embodiment of FIG. 4) so that 
water within the receptacle 70 above the predetermined discharge 
spill-over level overflows into the inner conduit 66 and is discharged out 
the outlet culvert 64. 
The upper end 78 of the inner conduit 66 is comprised of a plurality of 
detachable interlocking collar elements 82 for varying the vertical height 
of the overflow edge 80. Similarly, the upper end 74 of the outer conduit 
68 may be comprised of similar collar elements 82 for varying the 
predetermined vertical height of the surface water inlet overflow edge 76. 
Selective adjustment of the relative vertical heights of the inner and 
outer conduits 66, 68 provides control of the rate of discharge from the 
discharge control assembly 62 as well as control of the ratio of bottom 
water and surface water discharged in a manner similar to the discharge 
control assembly 10. A capped pipe 69 extends through the outer conduit 68 
and the inner conduit 66 at the deepest point and is adapted for removal 
of the cap 71 for interconnecting the conduits to the outlet culvert 64 to 
permit emptying of the lake as necessary. 
The bottom water conduit 20 is connected to a bottom water collector and, 
for water bodies which form an epilimnion, metalimnion and hypolimnion, 
the bottom water collector 22 shown in FIG. 1 may be utilized. 
Alternately, the bottom water collector 56 is utilized in shallow water 
bodies in accordance with the above-described explanation relative to the 
configurations of FIGS. 1 and 3. 
In operation, the heights of the inner and outer conduits 66, 68 are set by 
the interlocking collar elements 82 to the desired inlet spill-over level 
and discharge spill-over level respectively in accordance with the system 
hydrology. The withdrawal of bottom water from the lake into the 
receptacle 70 for discharge through the inner conduit 66 and discharge 
culvert 64 is controlled by the effective head of the control assembly 62 
and increases automatically as the lake level rises. The operation of 
control assembly 62 is similar to control assembly 10 and provides 
automatic gravitational discharge of bottom water relative to the height 
of the lake surface. Bottom water is automatically removed at a varying 
rate which depends upon the spill-over levels of the inner and outer 
conduits 66, 68 and the hydrologic conditions of the lake 13. Accordingly, 
the growth of aquatic weeds and algae is controlled and the quality of 
water is improved. 
Referring to FIG. 8, a third embodiment of the discharge control assembly 
of the present invention is shown and generally designated by the numeral 
84. The control assembly 84 is adapted for utilization with a body of 
water, such as lake 90, having an inlet stream 102, an outlet stream 14 
and an overflow spillway area 86. 
The control assembly 84 comprises a curtain partition 88 across the outlet 
end of the lake 90 to form a receptacle area 92 together with the side 
wall 94 of the lake. The curtain partition 88 is suspended vertically by a 
plurality of floats 94 at its upper end and has a plurality of weights 96 
at the lower end. The curtain partition 88 is suspended to a predetermined 
depth sufficient to force the outflow of water from the lake from the 
bottom cold-water layer, i.e., bottom water. The distance between the 
lower end 98 of the curtain partition 88 and the floor of the lake in 
effect forms an opening to the receptacle portion 92 to receive bottom 
water. Preferably, the volume of the receptacle portion 92 is 
predetermined to yield a residence time greater than three days based on 
the mean annual flow of the lake. In lakes where the deep layer or 
hypolimnion is not proximal to the outlet stream, an extension tunnel 100 
is connected to the lower end 98 of the vertical curtain partition 88 to 
facilitate withdrawal of bottom water. The extension tunnel 100 may be 
provided by a second curtain angled inwardly and downwardly from the lower 
edge of the vertical curtain 88 as diagrammatically shown in FIG. 8. A 
spillway system 110 similar to the inlet flashboard wall assembly 38 may 
be incorporated into the floatation discharge control assembly 84 as shown 
diagrammatically in broken line in FIG. 8 to attain a mixture of surface 
and bottom water outflow. 
In lakes where much of the inflow is from primary tributaries, such as the 
inlet stream 102, a thermal curtain partition 104 may be suspended across 
the inlet ends of the lake to force cool inflow water to the deep layer of 
the lake, (i.e., enhance interflow). The curtain or partition 104 is 
suspended by floats 106 and held vertically by the weights 108. The volume 
of water on the inflow side of the curtain partition 104 is minimized in 
order to avoid warming effects on the water inflowing into the deep layer. 
Alternately, a separate inlet collecting reservoir (not shown) and conduit 
(not shown) leading to the bottom of the lake may be utilized to enhance 
interflow. The enhanced interflow accordingly introduces watershed inputs 
of cool oxygen-rich water to the deep, cool layer and avoids direct 
watershed input of nutrients to the warm productive surface layer to 
thereby facilitate the control of aquatic weed and algae growth and 
enhance water quality. 
Accordingly, an apparatus and method for controlling the growth of aquatic 
macrophytes and algae is provided which alters the outflow configuration 
of the water body for controlled discharge of bottom water as well as 
surface water. The cool oxygen-deficient nutrient-rich bottom water is 
removed from the water body at a rate which automatically adjusts to 
varying hydrologic conditions without the need for pumping, siphoning, 
frequent adjustments, or large fluctuations in water level. Additionally, 
adjustable surface-bottom water outflow ratios are attained.