Abstract:
A method and apparatus for ensuring a minimum bypass flow installed in a stream wherein a diversion chamber is defined by front, rear and side panels, a screen, a bypass chamber and a second outlet chamber that allows water to flow into the second chamber only when the flow of water is sufficient.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/792,906 filed Mar. 15, 2013 for METHOD AND APPARATUS FOR ENSURING A MINIMUM BYPASS FLOW FROM A HYDROPOWER DIVERSION BOX and is incorporated by reference herein. 
    
    
     BACKGROUND AND FIELD 
     Standard diversion boxes are widely used to divert water from watercourses for water supply systems and hydroelectric power generation. Hydroelectric diversion boxes can divert a significant portion of the watercourse flow into a penstock (pipe) through which the water is conveyed to energize a turbine/generator to create electric power. The remaining, and often smaller, portion of the watercourse flow passes over the diversion box and downstream in the watercourse and is referred to as the “bypass flow.” Maintaining an adequate bypass flow is important because when the bypass flow falls below a specified volume, negative environmental impacts result to the riverine ecosystem and its aquatic life. 
     During periods of reduced natural water flow in a watercourse, such as that which occurs in summer drought periods, in a standard diversion box the bypass flow is reduced because the natural water flow has diminished but the water flow diverted to the penstock by the diversion box remains static. As a result, reduced natural water flow in the stream may reduce the health of the riverine ecosystem. 
     The present apparatus enhances the functionality of the standard diversion box by ensuring that the bypass flow will meet or exceed a specified volume and thus provide minimum bypass flow levels required to maintain healthy riverine ecosystems. As described herein, the present method and apparatus is designed such that the bypass flow takes precedence over flow diverted for hydropower generation and therefore ensures that minimum bypass flows are maintained to support the health of riverine ecosystems. 
     There is described herein an apparatus for ensuring a minimum bypass flow installed in a stream, having a diversion chamber having dual parallel side panels extending upwardly from outer edges of a floor panel and front and rear panels of varying height, a tilted wire wedge wire screen inclining downwardly and mounted between the side panels and the front and rear panels, a bypass chamber mounted within the diversion chamber having a bypass inlet and a bypass outlet, and a secondary chamber mounted within the diversion chamber and including an outlet port. The bypass chamber being defined by isolation walls, and the second outlet chamber mounted within the diversion box having second isolation walls with an open upper end and a penstock port, the second isolation walls being higher than the bypass inlet so that water flows into the second chamber only when the water level is above the second isolation walls. There is also provided a method of ensuring minimum bypass flow levels in a stream. 
    
    
     
       DETAILED DESCRIPTION OF DRAWINGS 
         FIG. 1  is a somewhat schematic view illustrating an intake unit containing a diversion box and penstock flow feature for conveying water into a turbine/generator; 
         FIG. 2  is an enlarged perspective view of the form of diversion box illustrated in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a tilted wire wedge wire screen; 
         FIG. 4  is a perspective view illustrating the interior of the unit shown in  FIGS. 1 &amp; 2 ; 
         FIG. 5  is a front view in elevation of the unit with the screen removed; 
         FIG. 6  is another cross-sectional view taken about lines  6 - 6  of  FIG. 5 ; and 
         FIG. 7  is a cut-away rear perspective view of the interior of the diversion box. 
     
    
    
     DETAILED DESCRIPTION 
     As a setting for the present apparatus, there is illustrated in  FIG. 1  a microhydro system which is typically installed in a stream as designated at S, the system comprising a diversion or intake box  10  at an upper level of the stream S having a penstock in the form of an elongated tubular section or pipeline  12  from an outlet  13  in the diversion box  10  into a turbine/generator  14  located at a lower elevation of the diversion box  10 . In this case, the particular turbine/generator  14  employed is commonly referred to as a microhydro turbine/generator which is capable of delivering from 0.5 to 50 kilowatts of electrical power. One commercial form of turbine/generator is the EcoHydro System™, manufactured and sold by Little Green Hydro, LLC of Hanover, N.H. 
     The EcoHydro System turbine/generator  14  has an electrical cable as indicated at  16  to direct electrical energy from the generator into a user facility such as a home, business or farm designated at H. The generator  14  is installed at a point downstream so as to have a difference in elevation or “head” beneath the diversion unit  10  to enable the flow of water under pressure via the penstock  12  from the diversion unit to operate the turbine generator  14 . A tail rack  18  returns the water flowing through the generator  14  back into the stream S as illustrated. It will be apparent that the diversion box  10  may be utilized in conjunction with splitters, not shown, to direct water flow through two or more penstock lines to a plurality of turbine/generators  14  located downstream of the diversion box. 
     As shown in  FIGS. 2-7 , one form of diversion box  10  is comprised of a chamber or box having front and rear panels  22  and  23 , respectively, and opposite side panels  24  and extending upwardly from outer edges of a bottom or floor panel  26 . The rear panel  23  is higher than the front panel  22  and terminates in an upper horizontal edge  28  above an upper horizontal edge  29  of the front panel  22 . In turn, the side panels  24  and  25  are of the same size and terminate in upper inclined edges  30  which extend downwardly from opposite ends of upper edge  28  of the rear panel to upper edge  29  of the front panel  22 . All of the panels may be of sheet metal or aluminum construction and with the adjoining edges rigidly interconnected to one another so as to define an upper inclined open support along the upper edges for mounting of a filter or screen  32 . Preferably the screen  32  is a tilted wire wedge wire screen with individual wedge wires  33  at an angle, preferably on the order of 5°, as shown in  FIG. 3  which will direct a selected amount of the water flowing over the screen into the interior of the box  10 . 
     The screen  32  is dimensioned to cover the entire upper open end of the box  10  and has an upper curved lip  34  in overhanging relation to the upper edge  28  of the rear panel  22 . The lower end of the screen has an extension  36  overhanging the upper edge  29  of the front panel  23  as shown in  FIG. 2 . The screen is supported by braces  38 , as shown in  FIG. 7  between the side panels  24  and  25  so as to rigidify the assembly of the screen to the box and maintain the screen at a slope or inclination on the order of preferably 30° to 45°. The extension plate  36  at the lower end of the screen  32  is in overhanging relation to the front panel  22  so that debris which collects on the self-cleaning screen will continue to advance downwardly with the water flowing over the top of the screen  32  into the stream. 
     A bypass chamber  40  is mounted in one lower front corner of the diversion box beneath the screen  32  and has a bypass inlet  42  in a rear isolation wall  45  above the bottom panel  26 , and a bypass outlet  44  in the front panel  22  of the diversion box communicates with the interior of the bypass chamber  40  as shown in  FIG. 7 . The bypass chamber itself is defined by isolation walls  45  and  46  at right angles to one another and joined to the front panel  22  and side panel  24 . The isolation wall panels  45  and  46  extend upwardly for the greater length or height of the panels  22  and  24  to which is attached a cover plate  48 . A second outlet chamber  50  for a penstock outlet port  52  is mounted in the sidewall  25 , and a  3 -sided or generally U-shaped vertical wall  54  is mounted in surrounding relation to the outlet port  52 , the chamber being open at its upper end as shown in  FIG. 6 . The wall  54  extends upwardly from the bottom panel  25  for a distance greater than the height of the bypass inlet  42  in order to regulate or control the relative amounts of water passing through the bypass chamber in relation to that utilized for the penstock flow during periods of low stream flow as hereinafter discussed in more detail. 
     Accordingly, in operation, and by reference to  FIG. 1 , the diversion box  10  is positioned in the stream S so that the screen  32  is positioned in the path of flow of the stream and the interior of the diversion box  10  will collect a portion of the water flow passing over the screen  32  into the interior of the box. The water influx will be divided between flow via the bypass chamber  40  through the bypass port  44  and the penstock port  52 . In addition, a portion of the water passing over the screen  32  will carry with it any debris which has collected on the screen. The greater amount of water under normal conditions which passes through the screen  32  will be directed through the bypass chamber  40  and returned into the stream S as bypass flow; and as long as the water level in the box is maintained above the isolation wall  54  surrounding the penstock port, water will flow through the penstock port and into pipeline  12  to operate the turbine/generator  14 . 
     A particular feature of maintenance of the bypass flow by this method and apparatus is that in periods of reduced natural water flows in a watercourse, such as may occur in summer drought periods, this embodiment ensures that the minimum specified volume of bypass flow will be met prior to water flow being diverted through the penstock port for hydropower generation, which has the highly beneficial effect of supporting the health of the riverine ecosystem. 
     Although one embodiment is herein set forth and described, the above and other modifications and changes may be made as well as their intended application for uses other than described without departing from the spirit and scope of the present method and apparatus.