FIELD OF THE DISCLOSURE

This disclosure relates to storm water management and in particular to a flow control device for a storm water management system.

BACKGROUND OF THE DISCLOSURE

Land development typically increases the peak flow rate of storm water runoff from a pre-development flow rateQ(cubic feet per second) as compared to a greater post-development peak flow rateQ′. A comparison of pre- and post-development hydrographs demonstrates not only the substantial increase in the peak flow rate fromQtoQ′, but also that the post-development peak flow rate occurs substantially earlier in the storm event.

Many jurisdictions require that storm water runoff from the boundary of developed land be managed so that the peak flow rateQ′for a specific rain event (for example, a particular storm such as a two-year storm or for a number of design storms) does not exceed the pre-development peak flow rateQ.

A jurisdiction may allow the peak flow rateQ′to increase as a function of storm intensity. As storm intensity increases from one design storm to the next design storm, the peak flow rateQ′increases as well.

A two-year storm at a given geographical location for example may require 2.91 inches of rainfall in a 24-hour period, a five-year storm 3.68 inches of rainfall in a 24-hour period, a ten-year storm 4.35 inches of rainfall in a 24 period, and a twenty-five year storm 5.40 inches of rainfall in a 24 period. Storm intensity data is available from state government agencies and from the US government's National Oceanic and Atmospheric Administration's National Weather Service Hydrometeorological Design Studies Center (which provides an online Precipitation Frequency Data Server (PFDS)).

A storm water management system manages storm water runoff from developed land.FIG. 31schematically illustrates in simplified form a storm water management system310. Storm water runoff is received into a storage chamber312via a storm drain314. Access to the interior of the storage chamber may be provided through a manhole (not shown). The storage chamber is fluidly connected to a discharge pipe316that discharges water from the system. Fluidly connected between the storage chamber and the discharge pipe is a flow control device illustrated as a valve318. The valve may be entirely or partially located within the storage chamber or may be located outside of the storage chamber. The valve limits the discharges rate of the storm water discharged into the discharge pipe so as to not exceed the maximum discharge rateQallowed by local regulation for a given storm event. This may involve a series of maximum discharge rates which are allowed for storms of different intensities.

During the period of the storm event in which the rate of storm water flow into the storage chamber exceeds the maximum allowable rateQ, the storage chamber stores the excess runoff for discharge later.

An ideal storm water management system minimizes the storage volume needed to store the excess runoff. An ideal storm water management system would initially discharge runoff at the same rate as the inflow rate into the system as allowed by regulation. The regulations may allow the discharge rate to increase with the intensity of the storm—a 5-year storm for example might have a higher allowable discharge rate than would a 2-year storm.

Typically, storm water management systems are allowed to initially discharge the maximum pre-development flow rate for the smallest design storm that is being regulated. As storm intensity increases, the system is allowed to progressively discharge the maximum pre-development flow rate for design storms of increasing intensity. This will be illustrated for a storm water management system that is allowed to discharge the maximum pre-development storm flow rate for a 2-year storm, then for a 10-year storm, and then for a 25-year storm. If the storm intensity increases beyond a 25-year storm, the storm water management system may reach full capacity and any excess storm water that cannot be stored in the system is discharged upon receipt into the system.

At the beginning of a storm event the illustrated storm water management system is allowed by regulation to discharge storm water at a maximum discharge rate equal to the pre-construction flow rate for a 2-year storm.

If the storm intensity increases beyond that of a 2-year storm the system's allowable maximum discharge rate steps up to the maximum pre-development storm flow rate for a 10-year storm.

If the storm intensity increases beyond that of a 10-year storm the system's allowable maximum discharge rate steps up to the maximum pre-development storm flow rate for a 25-year storm.

If the storm intensity increases beyond that of a 25-year storm, the storage chamber of the system may reach capacity. Excess storm water received into the system that cannot be stored is discharged at whatever rate it is being received into the system.

The number of design storms, the amount of rainfall associated with each design storm, and the maximum design storm a storm water management system must handle set out by regulation varies with geographical location and the needs of the jurisdiction. The maximum storm intensity is typically a 50-year storm or 100-year storm.

The ideal outlet hydrograph for a multi storm design is depicted in dashed lines inFIG. 18(and described in further detail below), which is a graph of the progressive allowable discharge rates for a complete maximum storm event. When the maximum storm has been exceeded, say a 100 year or a 50 year storm depending on regulations, the system is allowed to discharge whatever it is receiving by means of an overflow weir or maximum waterline outlet.

Typical storm water storage system regulations require that for any phase of the storm event, the system must retain the volume of water that exceeds the pre-development discharge for that phase of the event. A typical storm water management system stores the excess rainfall. The total storage required for the system is calculated using the design storms required by regulation.

At any time during a storm event, the storm may abate and the allowed maximum discharge rate may be reduced as the storage chamber empties. For example, a system that experiences a 5-year storm will be allowed to first discharge up to the 2-year pre-development maximum flow at the start of the storm and then discharge at the 5-year pre-development maximum flow after the storm exceeds the 2-year storm. If the storm abates sometime after reaching the intensity of a 2-year storm, the allowable discharge rate when the storm abates will be the 5-year pre-development maximum rate but will decrease to the 2-year pre-development maximum rate as the storage chamber empties.

Storage volume can be reduced significantly if the discharge rate from the storm water system is designed so as to discharge at the maximum rate allowed by regulation for each phase of the storm. Compared to some conventional outlet design strategies, releasing the maximum flow rates allowable can reduce the size of the system by as much as 50%, with typical reductions of 35%

Storm water management systems often use a flow control device that includes a storage chamber to receive and store runoff. The storage chamber may be provided with a discharge orifice of fixed size to discharge the stored runoff from the storage chamber. The orifice is sized for a discharge rate ofQwhen the storage chamber is full. The discharge rateQis often the maximum discharge rate allowed for the most severe storm subject to regulation.

Such storm water management systems do not approach the performance of an ideal storm water management system because they discharge water at a less than optimum rate when filling up. As a result, a storage system larger than the ideal storage system is required.

Other storm water management systems utilize multiple fixed orifices at different elevations or divert excess intake into other storage chambers. Although these systems may better approach the ideal system than a simple fixed orifice system, their performance may still be lacking or their costs and land use requirements are prohibitive for many projects.

Jurisdictions have begun allowing (or even requiring) the maximum discharge rate to be “stepped”, that is, allowing the maximum discharge rate to match the pre-development discharge rate as a function of storm severity or intensity for several different design storms. For example, a jurisdiction might allow a maximum discharge rate of 2.0 CFS for up to a two-year storm, s maximum discharge rate of 3.27 CFS between a two-year storm and a ten-year storm, a maximum discharge rate of 5.731 CFS between a ten-year storm and a twenty-five year storm, and a discharge rate of 7.97 CFS for between a twenty-five year storm and a fifty-year storm. If the storm intensity exceeds a 50-year storm, the design of the storm water management system results in the storage chamber becoming full and unable to accept additional storm water at a rate exceeding the maximum discharge rate of the system. Excess storm water that cannot be stored in the storage chamber is then allowed to discharge from the system without limit.

Increasing the allowed discharge rate with storm severity enables use of smaller storage chambers, with substantial cost savings.

Lang et al. U.S. Pat. No. 9,309,989 and Lang et al. U.S. Pat. No. 9,290,923, each assigned to the assignee of this application and incorporated by reference as if fully set forth herein, disclose storm water management systems and related flow control devices that better approach the performance of an ideal system. Although the systems and devices disclosed in the '989 and '923 patents offer design flexibility and work well, there is always a need to provide more options for optimizing performance of a storm water management system for a given land use situation.

BRIEF SUMMARY OF THE DISCLOSURE

Disclosed is a storm water management system that includes a flow control device that enables the system to approach the performance of an ideal system even when the maximum discharge rate is stepped or otherwise changes as a function of storm intensity.

Furthermore, the flow control device can be used in both above-ground and below-ground storm water management systems. The flow control device can be used in new construction, or can be retro-fitted to existing storm water management systems. Portions of the flow control device can be prefabricated, with project-specific components easily added later or on-site.

The flow control device in embodiments of the disclosed system includes a valve fluidly disposed between a storm water storage chamber and a discharge of the system. The valve has a movable valving member and a fixed valving member. The valving members cooperate with one another to define a variably-sized orifice disposed between the storage chamber and the discharge. The orifice can be located at either an intake end of the valve, a discharge end of the valve, or the orifice can include orifice portions at both the intake and discharge ends of the valve.

The size or flow area of the discharge orifice is a function of the relative position of the two valving members with respect to one another. The movable valving member is operatively connected to a float whose position in the storage chamber is a function of the water level in the chamber.

The discharge orifice discharges into a discharge pipe that flows storm water out of the storage chamber.

In a first set of embodiments of the disclosed system the float and the movable valving member are connected together by a scissors mechanism. The scissors mechanism converts movement of the float to movement of the movable valving member. In this first set of embodiments the scissors mechanism is attached between the float and the valving member in a number of different ways. The movable valving member in some embodiments moves parallel with the float movement. In other embodiments the movable valving member moves transverse to the float movement.

In a second set of embodiments of the disclosed system each valving member has a thickness and a through opening extending through the thickness of the member. The movable valving member overlays the fixed valving member. The through openings overlay one another throughout a range of relative motion of the movable member with respect to the fixed valving member. The overlaying through openings cooperate with one another to define the instantaneous flow area of the valve discharge orifice as a function of the relative positions of the valving members.

The rate of change of the flow area at any given instant may be zero (that is, the instantaneous rate of change of the flow area is zero and so the flow area is constant), positive (that is, the instantaneous rate of change of the flow area is positive and the flow area is increasing), or negative (that is, the instantaneous rate of change of the flow area is negative and the flow area is decreasing). The rate of change of the flow area may effectively be discontinuous, that is, the discharge size may exhibit a step change having a non-continuous increase or decrease in flow area.

The discharge orifice flow area as a function of float displacement of the valve can be defined by the engineer through the design of the through openings of the valving members. Step changes in orifice flow area for example may accommodate step changes in discharge rates allowed by a jurisdiction as a function of storm severity.

In some embodiments of the second set of embodiments the fixed valving member is attached to the intake end of the discharge pipe. The through opening of the fixed valving member discharges directly into the intake end of the discharge pipe.

The cross sectional area of the discharge opening of the fixed valving member defines the largest possible flow area of the discharge orifice.

The movable valving member through opening discharges into the fixed valving member through opening. The movable valving member through opening extends in the direction of the relative movement of the movable valving member. The fixed valving member through opening continuously becomes located over a different portion of the movable valving member through opening as the float moves between raised and lowered positions. In this embodiment the instantaneous flow area of the discharge orifice is defined by the flow area of the movable valving member through opening portion being overlaid by the fixed valving member through opening. The movable valving member through area narrows or widens along the direction of relative movement to vary the valve orifice size with float displacement as desired.

In some embodiments of the second set of embodiments the valve discharge opening defined by the cooperating valving member through openings may be zero (closing the orifice) for some position or relative range of positions of the valving members. For example, the valve may remain closed until the float has raised some predetermined amount after the start of a storm event and thereby delay initial storm water discharge from the valve.

The position of the movable valving member through opening relative to the fixed valving member through opening may be offset in the direction of relative displacement to delay the opening of the discharge opening.

The movable and fixed valving members of the second set of embodiments may be formed as tubular members, one valving member being closely received inside the other valving member. Storm water may flow into the inner valving member and flow out the valve member through openings for discharge. The valving members may translate relative to one another along an axis. The valving members may formed as circular cylinders and either translate or rotate relative to each other along or about a common cylinder axis. In yet other possible embodiments the valving members may be formed as flat plates that translate with respect to one another along an axis. In yet further other possible embodiments the valving members may be formed as portions of a sphere that rotate about a common point with respect to one another.

The movable valving member in possible embodiments may be attached to a scissors mechanism, that is, embodiments of the disclosed storm water management system may be members of both the first and second sets of embodiments. In other possible embodiments the movable valving member may be attached to a lever mechanism or other conventional mechanism for converting relative movement of one member to relative movement of another member.

Other objects and features of the disclosure will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawing sheets.

