AU2012308798B2

AU2012308798B2 - Bridge system and method including four sided concrete bridge units adapted for promoting sedimentation

Info

Publication number: AU2012308798B2
Application number: AU2012308798A
Authority: AU
Inventors: Scott D. Aston; Michael A. Blank; Edward H. Zax
Original assignee: Contech Engineered Solutions LLC
Current assignee: Contech Engineered Solutions LLC
Priority date: 2011-09-16
Filing date: 2012-09-12
Publication date: 2016-10-27
Anticipated expiration: 2032-09-12
Also published as: DK2756135T3; EP2756135A2; AR087890A1; WO2013039970A2; ES2656858T3; EP2756135B1; CA2848200A1; AU2012308798A1; PL2756135T3; US20130071189A1; WO2013039970A3

Abstract

A method of providing an environmentally appealing region for water flow along an surrounded pathway tunnel involves providing a plurality of four-sided concrete bridge units in abutting relationship to create a surrounded pathway tunnel, one end of the tunnel located upstream along a water path and an opposite end of the tunnel located downstream along the water path; allowing water to flow through the surrounded pathway tunnel during a rain or other flow event; and providing a multiplicity of the four-sided bridge units with a corresponding bottom wall structure that interacts with the flowing water and earthen material in the flowing water such that capture and settling of the earthen material at locations along the tunnel occurs to produce a more natural water flow pathway along the tunnel.

Description

BRIDGE SYSTEM AND METHOD INCLUDING FOUR SIDED CONCRETE BRIDGE UNITS ADAPTED FOR PROMOTING SEDIMENTATION 2012308798 11 Mar 2014

CROSS-REFERENCES

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 61/535,565, filed September 16, 2011, which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The present application relates to the general art of precast concrete bridge and culvert units, and to the particular field of four-sided bridge and culvert units.

BACKGROUND

[0002a] A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

[002b] Where the terms “comprise”, “comprises”, “comprised” or “comprising” are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.

[0003] Overfilled bridge structures are frequently formed of precast reinforced four-sided concrete units commonly referred to as arch units, arch culverts, box units or box culverts. As used herein the terminology four-sided bridge unit encompasses all of such structures. The units are used in the case of bridges to support one pathway over a second pathway, which can be a waterway. Four-sided bridge units have a bottom wall structure that facilitates on-site placement with reduced need for foundation preparation.

[0004] In the past, the four-sided bridge units of overfilled bridge structures have been constructed with bottom wall structures having a generally planar and continuous top surface and a generally uniform thickness. There is an increasing demand for construction efforts to provide more natural environments and/or to decrease impact on wildlife.

[0005] A four-side bridge unit adapted to create a more natural environment through the pathway defined by the bridge units and/or adapted to reduce impact on fish migrations would be desirable.

SUMMARY

[0006] In one aspect of the present invention there is provided a method of 1 providing an environmentally appealing region for water flow along a surrounded pathway tunnel, the method comprising: providing a plurality of four-sided precast concrete bridge units in abutting relationship to create a surrounded pathway tunnel, one end of the tunnel located upstream along a water path and an opposite end of the tunnel located downstream along the water path, each of the four-sided precast concrete bridge units including spaced apart side walls interconnected by a top wall and a bottom wall; allowing water to flow through the surrounded pathway tunnel during a rain or other flow event; and providing a multiplicity of the four-sided precast concrete bridge units with a corresponding precast bottom wall configuration having a plurality of through openings that interact with the flowing water and earthen material in the flowing water such that capture and settling of the earthen material at locations along the tunnel occurs to produce a more natural water flow pathway along the tunnel; wherein each of the plurality of through openings of the bottom wall of each of the multiplicity of the four-side precast concrete bridge units is configured as an elongated slot that extends from one side wall to the other side wall of the respective four-sided precast concrete bridge unit to provide connectivity between the pathway tunnel and the underlying earth along a full span of the pathway tunnel, and wherein the bottom wall configuration of each of the multiplicity of the four-side precast concrete bridge units includes multiple elongated precast concrete beams that extend from one side wall to the other side wall of the respective four-sided precast concrete bridge unit to provide separation between the elongated slots, each elongated precast concrete beam extending along the full span of the pathway tunnel, and each elongated precast concrete beam having a bottom side that is in a common plane with a bottom side of each of the side walls so as to aid in transferring load to ground below the unit, wherein the elongated precast concrete beams are each configured to, in combination, create a low flow channel along a depth of the pathway tunnel and through which marine life can travel, wherein at least one elongated precast concrete beam of each of the multiplicity of the four-sided precast concrete bridge units has a configuration that is different than a configuration of another one of the elongated precast concrete beams of the precast four-sided concrete bridge unit. 2012308798 11 Mar 2014 [0007] The bottom wall structure of each of the multiplicity of the four-sided bridge units may be provided with a plurality of through openings such that at least forty percent of the bottom wall structure is open. For example, at least fifty percent of the bottom wall structure of each of the multiplicity of the four-sided bridge units may be open. 2 [0008] A lip structure may be provided at a top portion of at least some of the through openings, the lip structure facing upstream. 2012308798 11 Mar 2014 [0009] The plurality of openings of each bottom wall structure may be arranged in rows that extend along a span of the respective four-sided bridge unit.

[0010] The plurality of openings may be formed in the shape of elongated slots, each elongated slot defining a row, such that multiple beams are formed in the bottom wall structure and also extend along the span. At least one beam with a height that is greater than a height of another beam, the higher beam interacting with the flowing water and earthen material to reduce flow velocity and thereby enhance settling out of earthen material. By providing a lip structure along at least one beam, the lip structure extending in an upstream direction into an adjacent elongated slot, wash out of earthen material that has settled in the adjacent elongated slot can be limited.

[0011] The plurality of openings may be provided as multiple series of openings, each series of openings forming a respective row. By staggering openings of adjacent rows, nesting of the openings is achieved. By providing upper lip structure along one or more edges of at least some of the openings, the lip structure extending into its respective opening, wash out can be limited.

[0012] By providing the bottom wall structure of each of the multiplicity of the four-sided bridge units with a recessed portion, a low flow channel through which marine life can travel is created.

[0012a] According to another aspect of the present invention, there is provided an overfilled bridge system, comprising: a plurality of four-sided precast concrete bridge units arranged in abutting relationship to create a surrounded pathway tunnel, one end of the tunnel located upstream along a water path and an opposite end of the tunnel located downstream along the water path, each of the four-sided precast concrete bridge units including spaced apart side walls interconnected by a top wall and a bottom wall; wherein the bottom wall each of a multiplicity of the four-sided precast concrete bridge units includes a plurality of through openings to interact with the flowing water and earthen material in the flowing water such that capture and settling of the earthen material at multiple locations along the tunnel occurs to produce a more natural water flow pathway along the tunnel; wherein each of the plurality of through openings of the bottom wall of each of the multiplicity of the four-sided precast concrete bridge units is configured as an elongated slot that extends from one side wall to the other sidewall of the respective four 2a -sided precast concrete bridge unit to provide connectivity between the pathway tunnel and the underlying earth along a span of the pathway tunnel, and wherein the bottom wall of each of the multiplicity of the four-side precast concrete bridge units includes multiple elongated precast concrete beams that extend from one side wall to the other side wall of the respective four-sided precast concrete bridge unit to provide separation between the elongated slots, each elongated precast concrete beam extending along the full span of the pathway tunnel, and each elongated precast concrete beam having a bottom side that is a common plane with a bottom side of each of the side walls so as to aid in transferring load to ground below the unit, wherein the elongated precast concrete beams are each configured to, in combination, create a low flow channel along a depth of the pathway tunnel and through which marine life can travel, wherein at least one elongated precast concrete beam of each of the multiplicity of the four-sided precast concrete bridge units has a configuration that is different than a configuration of another one of the elongated precast concrete beams of the four-sided precast concrete bridge unit. 2012308798 11 Mar 2014 [0012b] According to another aspect of the present invention, there is provided a structure, comprising: a four-sided precast concrete bridge unit buried in earthen material, the four sided precast concrete bridge unit having a top wall, a bottom wall and first and second side walls connecting the top wall to the bottom wall, wherein the bottom wall includes multiple openings therein for allowing water to infiltrate through the bottom wall into the earthen material, each opening configured as an elongated slot that extends from the first side wall to the second side wall, the elongated slots separated from each other by elongated precast concrete beams of the bottom wall, each elongated precast concrete beam extending from the first side wall to the second sidewall, each elongated precast concrete beam having a bottom side resting on the earthen material so as to aid in transferring load to ground below the unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig. 1 is a perspective view of one embodiment of a four-sided bridge unit; [0014] Fig. 2 is an end elevation of the bridge unit of Fig. 1; [0015] Fig. 3 is a cross section along line 3-3 of Fig. 2; [0016] Fig. 4 is bottom view of the bridge unit of Fig. 1; [0017] Fig. 5 is a cross-sectional view of two bridge units of Fig. 1 arranged edge to edge; [0018] Fig. 6 is an enlarged partial view of the cross-section of Fig. 5; 2b PCT/US2012/054757 WO 2013/039970 [0019] Fig. 7 shows a partial cross-section of an embodiment of a unit with both upstream and downstream facing lips; [0020] Fig. 8 shows a partial cross-section of an embodiment of a unit in which the beams all have a common height; [0021] Figs. 9 and 10 show perspective views of another embodiment of a foursided bridge unit in which continuous haunches are provided in the comers where the bottom wall meets the side walls; [0022] bridge unit; [0023] [0024] [0025] [0026] [0027] bridge unit; [0028] [0029] [0030] [0031] [0032] [0033] [0034] path; and [0035]

Fig. 11 is a perspective view of yet another embodiment of a four-sided

Fig. 12 is an end elevation of the bridge unit of Fig. 11;

Fig. 13 is a cross section along line 13-13 of Fig. 12;

Fig. 14 is bottom view of the bridge unit of Fig. 11;

Fig. 14A is a partial cross-section along line 14A of Fig. 14;

Fig. 15 is a perspective view of still another embodiment of a four-sided

Fig. 16 is an end elevation of the bridge unit of Fig. 15;

Fig. 17 is a cross section along line 17-17 of Fig. 16;

Fig. 18 is bottom view of the bridge unit of Fig. 15;

Figs. 19A-B show another embodiment of a bridge unit;

Fig. 20A-C show another embodiment of a bridge unit;

Fig. 21A-C show another embodiment of a bridge unit;

Fig. 22 shows a plurality of four-sided units arranged along a water flow

Fig. 23 shows a schematic end elevation of the system of Fig. 22 as buried. DETAILED DESCRIPTION

[0036] Referring to Figs. 1-4, a four-sided precast concrete bridge unit 10 is shown.

In the illustrated embodiment bridge unit 10 is formed by a generally horizontal extending bottom wall 12, substantially vertically upward extending side walls 14 and 16 at the ends of the bottom wall and a top wall 18 having a generally arch-shaped configuration. However, four sided bridge units having top walls other than arch-shaped (e.g., flat top walls) are also contemplated. Likewise, side walls other than vertical are possible. As used herein, the terms "length" and "span" of an individual unit or portions of the unit refers to a horizontal dimension extending parallel with the direction of arrow 20 (which is 3 PCT/US2012/054757 WO 2013/039970 substantially perpendicular to a horizontal through axis 22 of the unit) and the terms "width" and "depth" of the individual unit or portions of the unit refer to a horizontal dimension extending parallel to the through axis 22. As used herein the term "arch" and "arch-shaped" when referring to the top of an arch unit means a curved shape (including constant radius curves, curves with multiple radii, curves with continuously varying radius) or any top wall shape that is higher in the middle of the top wall as opposed to where the top wall meets the side walls (e.g., an inverted V-shape or a combination of three or more planar segments angularly arranged with respect to each other to produce a vaulted top wall or a combination of curved segments and flat segments that produce a vaulted top wall).

[0037] The bottom, top and side walls are preferably precast as a single monolithic structure in a single casting operation. However, in certain implementations, one or more walls may be cast separately and then connected together by suitable connecting structure (e.g., reinforcing bars or by casting one or more elements separately and then placing that cast element in the formwork that is used to cast the final structure).

[0038] The bottom wall 12 of the unit 10 is shaped and configured to facilitate both sedimentation within and passage of marine life once the unit is installed. Specifically, the bottom wall 12 includes a plurality of elongated, spanwise extending through openings that extend completely through the thickness of the bottom wall 12. As shown, each elongated opening 24 has a length Lo that is at least about sixty percent of the overall width of the unit Lu (e.g., Lo is at least about 70% of Lu, such as for example, between 80% and 95% of Lu). However, other variations are possible. Intermediate beams 26 separate the elongated openings 24 and serve to maintain a rigid connection between the lower ends of the side walls 14 and 16. Edge located beams 28 are also provided, thereby providing a continuous peripheral support surface at the lower side of the bottom wall. The lower surface of each beam 28 is preferably in common plane with the continuous peripheral support surface to provide added stability and distribution of loads. As shown, roughly about 40% to 60% (e.g., about 45% to 55%) of the lower side of the bottom wall makes up the support or resting surface of the bridge unit and the remainder (about 60% to 40%) is open via the openings 24. However, other variations are possible. Lengthwise extending reinforcement may be provided in each of the beams for structural integrity, with some continuity provided between that reinforcement and the reinforcement of the vertical side walls.

[0039] As seen in Fig. 3, where the anticipated water flow direction through the bridge unit is shown by arrow 30, the combination of the beams 26, 28 and the openings 24 4 PCT/US2012/054757 WO 2013/039970 are configured to promote sedimentation at the bottom of the bridge unit. Specifically, the beams 26 and one of the beams 28 are formed with a lip structure 32 and 34 that overhangs the adjacent opening 24 and extends from the beam in an upstream direction. Also, one or more of the beams 28 has a thickness or height that exceeds that of the adjacent beams 26 and/or 28. The effect of this configuration is best described with reference to Figs. 5 and 6, where Fig. 5 shows two units 10 in edge to edge relationship as such units would typically be installed on a job site and Fig. 6 shows an enlarged partial view with a flow pattern.

[0040] As seen in Fig. 5, the edge located beams 28" (located at the upstream flow edge of the units) lack any upstream facing lip structure while the edge located beams 28' (located at the downstream flow edge of the units) incorporates an upstream facing lip structure. In this manner, when two units 10 are installed edge to edge, there is no lip structure to interfere with the placement and the adjacent beams 28' and 28" combine to form effective beam that is similar in overall configuration and size to intermediate beam 26'. In this regard, the width of the beam structures 28' and 28" is preferably smaller than the width of beam structures 26' and 26" (e.g., on the order of about 50% to about 60% of the width of beam structures 26' and 26") so that the overall width of the effective beam is more consistent with the overall width of the beams 26' and 26". The height of beams 26" is greater than the height of beams 26', 28' and 28" as shown. Beams 26', 28' and 28" have the same thickness or height and beams 26" may have a thickness or height that is about 110% to about 140% greater (e.g., about 120% to about 130% greater). However, variations are possible. The width Wl of the lip structure may be on the order of about 10% to 20% of the overall width Wo of the opening 24. In the illustrated embodiment, a tapered surface 36 connects the vertical side surface 38 of the beam with the protruding edge of the lip.

[0041] Referring to Fig. 6, as water flows through the units the higher beams tend to reduce the velocity in the vicinity 40 of an opening 24 which tends to cause sediment to drop out of the flow and into the opening. The lip structure 32 helps prevent washout of any sediment that builds up in the openings 24. The lip structures 32 and 34 of the shorter beams 26' and 28' also help prevent washout in respective openings and creates respective areas 42 and 44 of lower velocity that can promote sedimentation.

[0042] In the illustrated embodiment, the connection of every other beam to the vertical side wall includes a haunch 46, which may include reinforcement, to resist the moment loads in the comers. Placing the haunches in a spaced apart manner, rather than 5 PCT/U S2012/054757 WO 2013/039970 providing a continuous haunch, can also help promote sedimentation. However, continuous haunches are also contemplated for some applications, as reflected in the embodiment of Figs. 9 and 10. In this embodiment, the relative length of the slotted openings 24 (as compared to overall length of the unit) is smaller than that shown in Fig. 4 in order to accommodate the haunch 46. Moreover, Figs. 9 and 10 show a four-sided bridge unit with a flat top wall structure rather than an arched top wall structure.

[0043] While the embodiment of Figs. 1-6 contemplates upstream facing lips only, in an alternative embodiment downstream facing lips may also be provided on the beams as shown in Fig. 7. Likewise, embodiments in which all the beams have a common height are contemplated, as shown in Fig. 8.

[0044] Referring again to Figs. 1, 2 and 4, and regardless of the relative height of the plurality of beams, each of the beams may be formed with a section 48 of reduced thickness to create a low flow channel through the unit, making it easier for marine life (e.g., fish) to travel through the unit. The reduced thickness sections 48 may be formed without any lip structures.

[0045] An alternative embodiment of a four-side bridge unit 50 adapted for sedimentation is shown in Figs. 11-14. As shown, the bottom wall 52 of the bridge unit 50 includes a plurality of openings 54. The openings are arranged in a plurality of lengthwise extending rows 56 and 58, with the rows 56 and 58 arranged in an alternating and staggered relationship that provides some nesting of the openings of one row into the spaces between the openings of another row. The openings are distributed along a lengthwise extending mid-portion L0 of the bottom wall 52 that represents between about 50% to about 80% of the overall length Lu of the bottom wall of the unit. In this manner, the bottom wall lacks any openings in roughly about the first 10% to 25% of the extent of the bottom wall from its ends. Reinforcement 60 may be located in this area for structural integrity. Likewise, as the edges of the bottom wall are continuous, lengthwise reinforcement 62 may be included along such edges as well. About 75% to about 90% of the bottom wall in the mid-portion Lo may be open space, while only about 55% to about 70% of the overall area of the bottom wall (as viewed from the bottom) may be open space. As shown in Fig. 14A, the openings 54 may include lip structure to promote sedimentation and reduce washout effects. The lip structure may be upstream facing lip structure 66, downstream facing lip structure 64 and/or lengthwise facing lip structure 68.

[0046] A further embodiment of a four-sided bridge unit 70 is shown in Figs. 15- 6 18. In this embodiment the openings 74 of the unit actually include rows of partial openings along each edge. The partial openings 74' are preferably about one half the size of a regular opening such that when one unit is abutted with another unit the partial openings combine to effectively form an opening similar in size and shape to the openings 74. The mid-point arrangement of the openings along the length of the bottom wall 72 may be similar to that of the embodiment of Figs. 11-14, with reinforcement 76 in the end areas of the bottom wall 72. However, due to the edge openings 74', no reinforcement is provided in the mid-section where the openings are located. The openings 74 of the unit 70 may also include lip structure as described relative to Fig. 14A. 2012308798 11 Mar 2014 [0047] It is to be clearly understood that the above description is intended by way of illustration and example only and is not intended to be taken by way of limitation, and that changes and modifications are possible. For example, other possible unit configurations are reflected in Figs. 19A-B, 20A-C and 21A-C. For reference, the unit 90 of Figs. 19A-B includes lengthwise extending openings 82 having ends adjacent the side walls 84, alternatingly raised 86 and lowered 88 beams and upstream facing lips, with no haunches or gusseting between the bottom wall and the side walls. The unit 90 of Figs. 20A-C is similar to that of Figs. 19A-B but also includes reduced thickness sections in the beams to provide a low flow channel 92. The unit 100 of Figs. 21A-C includes beams and slots with ends spaced from the side walls, and no haunches or gussets, such that the comer areas between the bottom wall and the side walls form low flow areas.

[0048] Fig. 22 shows a plurality of four-sided concrete bridge units, which could be any of the unit configurations previously described, in abutting relationship to create a surrounded pathway tunnel 110. One end 112 of the tunnel is located upstream along a water path 114 and an opposite end 116 of the tunnel is located downstream along the water path 114. Fig. 23 shows the units in profile as buried in earthen material 118. Fig. 23 could also represent a series of buried units used for the purpose of storm water collection, with infiltration into the surrounding earth occuring through the openings in the bottom walls of the units.

[0049] Other embodiments are contemplated and modifications and changes could be made without departing from the scope of this application. 7

Claims

The claims defining the invention are as follows:

1. A method of providing an environmentally appealing region for water flow along a surrounded pathway tunnel, the method comprising: providing a plurality of four-sided precast concrete bridge units in abutting relationship to create a surrounded pathway tunnel, one end of the tunnel located upstream along a water path and an opposite end of the tunnel located downstream along the water path, each of the four-sided precast concrete bridge units including spaced apart side walls interconnected by a top wall and a bottom wall; allowing water to flow through the surrounded pathway tunnel during a rain or other flow event; and providing a multiplicity of the four-sided precast concrete bridge units with a corresponding precast bottom wall configuration having a plurality of through openings that interact with the flowing water and earthen material in the flowing water such that capture and settling of the earthen material at locations along the tunnel occurs to produce a more natural water flow pathway along the tunnel; wherein each of the plurality of through openings of the bottom wall of each of the multiplicity of the four-side precast concrete bridge units is configured as an elongated slot that extends from one side wall to the other side wall of the respective four-sided precast concrete bridge unit to provide connectivity between the pathway tunnel and the underlying earth along a full span of the pathway tunnel, and wherein the bottom wall configuration of each of the multiplicity of the four-side precast concrete bridge units includes multiple elongated precast concrete beams that extend from one side wall to the other side wall of the respective four-sided precast concrete bridge unit to provide separation between the elongated slots, each elongated precast concrete beam extending along the full span of the pathway tunnel, and each elongated precast concrete beam having a bottom side that is in a common plane with a bottom side of each of the side walls so as to aid in transferring load to ground below the unit, wherein the elongated precast concrete beams are each configured to, in combination, create a low flow channel along a depth of the pathway tunnel and through which marine life can travel, wherein at least one elongated precast concrete beam of each of the multiplicity of the four-sided precast concrete bridge units has a configuration that is different than a configuration of another one of the elongated precast concrete beams of the precast four-sided concrete bridge unit.
2. The method of claim 1, wherein at least forty percent of the bottom wall of each of the multiplicity of the four-sided precast concrete bridge units is open.
3. The method of claim 2, wherein at least fifty percent of the bottom wall of each of the multiplicity of the four-sided precast concrete bridge units is open.
4. The method of claims 2 or 3, further comprising providing a lip structure at a top portion of at least some of the through openings, the lip structure facing upstream. 5 The method of any one of claims 1 to 4, further comprising providing at least one beam of each of the multiplicity of the four-sided precast concrete bridge units with a height that is greater than a height of another beam of the four-sided precast concrete bridge unit, the higher beam interacting with the flowing water and earthen material to reduce flow velocity and thereby enhance settling out of earthen material, the higher beam separated depthwise along the four-sided precast concrete bridge unit from the lower beam by at least one elongated slot.
6. The method of claim 5, further comprising providing a lip structure along at least one beam, the lip structure extending in an upstream direction into an adjacent elongated slot and acting to limit wash out of earthen material that has settled in the adjacent elongated slot.
7. The method of any one of claims 2 to 6, wherein in each of the multiplicity of the four-sided precast concrete bridge units haunch sections connect the bottom wall with side walls of the respective four-sided precast concrete bridge unit.
8. An overfilled bridge system, comprising: a plurality of four-sided precast concrete bridge units arranged in abutting relationship to create a surrounded pathway tunnel, one end of the tunnel located upstream along a water path and an opposite end of the tunnel located downstream along the water path, each of the four-sided precast concrete bridge units including spaced apart side walls interconnected by a top wall and a bottom wall; wherein the bottom wall each of a multiplicity of the four-sided precast concrete bridge units includes a plurality of through openings to interact with the flowing water and earthen material in the flowing water such that capture and settling of the earthen material at multiple locations along the tunnel occurs to produce a more natural water flow pathway along the tunnel; wherein each of the plurality of through openings of the bottom wall of each of the multiplicity of the four-sided precast concrete bridge units is configured as an elongated slot that extends from one side wall to the other sidewall of the respective four-sided precast concrete bridge unit to provide connectivity between the pathway tunnel and the underlying earth along a span of the pathway tunnel, and wherein the bottom wall of each of the multiplicity of the four-side precast concrete bridge units includes multiple elongated precast concrete beams that extend from one side wall to the other side wall of the respective four-sided precast concrete bridge unit to provide separation between the elongated slots, each elongated precast concrete beam extending along the full span of the pathway tunnel, and each elongated precast concrete beam having a bottom side that is a common plane with a bottom side of each of the side walls so as to aid in transferring load to ground below the unit, wherein the elongated precast concrete beams are each configured to, in combination, create a low flow channel along a depth of the pathway tunnel and through which marine life can travel, wherein at least one elongated precast concrete beam of each of the multiplicity of the four-sided precast concrete bridge units has a configuration that is different than a configuration of another one of the elongated precast concrete beams of the four-sided precast concrete bridge unit.
9. The system of claim 8, further comprising: earthen material, deposited from flowing water, settled at the multiple locations.
10. The system of claims 8 or 9, wherein at least forty percent of the bottom wall of each of the multiplicity of the four-side precast concrete bridge units is open.
11. The system of claim 10, wherein at least fifty percent of the bottom wall of each of the multiplicity of the four-sided precast concrete bridge units is open.
12. The system of any one of claims 8 to 11, wherein at least some of the through openings include an upper lip structure at least part of which faces upstream.
13. The system of any one of claims 8 to 12, wherein at least a first one of the elongated precast concrete beams of each of the multiplicity of four-sided bridged units has a height that is greater than a height of a second one of the elongated precast concrete beams, the first elongated precast concrete beam configured to interact with the flowing water and earthen material to reduce flow velocity and thereby enhance settling out of earthen material, the first elongated precast concrete beam separated from the second elongated precast concrete beam by at least one of the elongated slots.
14. The system of claim 13, wherein the first elongated precast concrete beam includes an upper lip structure extending in an upstream direction into an adjacent elongated slot and is configured to limit wash out of earthen material that has settled in the adjacent elongated slot.
15. A structure, comprising: a four-sided precast concrete bridge unit buried in earthen material, the four sided precast concrete bridge unit having a top wall, a bottom wall and first and second side walls connecting the top wall to the bottom wall, wherein the bottom wall includes multiple openings therein for allowing water to infiltrate through the bottom wall into the earthen material, each opening configured as an elongated slot that extends from the first side wall to the second side wall, the elongated slots separated from each other by elongated precast concrete beams of the bottom wall, each elongated precast concrete beam extending from the first side wall to the second sidewall, each elongated precast concrete beam having a bottom side resting on the earthen material so as to aid in transferring load to ground below the unit.
16. The structure of claim 15 wherein the elongated precast concrete beams are each configured so as to, in combination, create a low flow channel along a depth of the precast concrete bridge unit and through which marine life can travel, wherein at least one of the elongated precast concrete beams has a configuration that is different than a configuration of another one of the elongated precast concrete beams.