Idea Transcript
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3.0 PRELIMINARY NATURAL CHANNEL DESIGN This section of the report provides the design details of the preferred stream channel alignment within the Red Hill Creek Valley. As mentioned in Section 2.0, a master restoration plan/design has been developed which details the channel alignment between the Bruce Trail foot bridge (most southerly limit) and approximately 400m down stream of the CNR railway (most northerly limit). Rationalization for the particular alignment was discussed in Section 2.0. This section outlines the physical setting and preliminary design components of the proposed creek alignment. The information used in developing the natural channel design was primarily obtained from field work exercises that are outlined in Section 1.0 of this report. Also, information from Annable [1996] and Annable [1995b] were used as supplemental information in assisting with the design parameters. Further, general design strategies offered by Rosgen [1996] and Newbury and Gaboury [1993] were also incorporated into the design analysis and layout. The hydraulic analysis for the proposed stream design was jointly undertaken between Water Regime and Philips Engineering Ltd. Since Philips Engineering Ltd. was retained to undertake the storm water quantity / quality and flood plain assessment for bridge structures etc. within the watershed, hydraulic analysis for the creek design was most practically undertaken as an extension of these works with technical collaborations from Water Regime. Therefore the hydraulic analysis with respect to the stream design can be found in Philips Engineering Ltd. [2002].
3.1 Stream Design Designing a natural channel is an iterative procedure incorporating the cross-sectional form of the channel and the meander geometry which is in balance with the existing watershed flow regime and the sediment supply (including the range in grain sizes). The general approach for design is similar to that outlined by Annable [1999] (Appendix I) and is illustrated in Figure 3-1. The discussion that follows rationalizes the specific design parameters for reach-based segments of the stream with similar morphologies and discharge regimes. The fundamental assumption in employing the natural channel design approach is that a long-term stable channel in dimension, pattern and profile is the objective. Considering the topographic relief of the lower watershed and the proposed land use planning constraints outlined in Section 2.0, two stable stream morphologies are utilized to meet all of the land use objectives. First, a riffle-pool dominated morphology (C-type stream) is proposed in areas where valley confinement is minimal or topographic relief is less than approximately 1%. In steeper gradient areas (such as the escarpment) or where narrow corridors exists a step-pool morphology (B-type stream) is most appropriate. Additional assumptions were made with respect to the stream channel design as a result of the continued impact assessment with the City’s consulting team and staff. These assumptions are: Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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•
an additional CSO tank would be constructed in the Greenhill Ave. area to reduce the current frequency of discharge from the Greenhill C.S.O. facility. The design discharge frequency to the creek should be reduced from the present frequency of bankfull discharge observed at the Mount Albion gauge (averaging 6 times per year) to approximately 1 - 2 times per year. The CSO discharge would only discharge to the creek when Red Hill creek was flowing in excess of approximately 15 m3/s. Thus, discharge occurring from this facility would occur at a stage above bankfull and be displaced onto the flood plain minimizing stream power and minimizing stream channel erosion. Therefore, bankfull discharge between Mount Albion Falls and the Davis creek tributary would remain essentially constant and a unique system of design parameters were developed for this reach,
Figu re 3-1 N atural C han nel D esign Ap pr oach
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the King St., Queenston Ave. and Melvin St. combined storm sewer discharges into the creek will be discontinued and routed through a proposed linear combined sewer overflow facility (i.e. tunnel) below the proposed expressway. This facility will discharge to the STP with a relief overflow at a location downstream of Barton St. within the backwater effects of Lake Ontario and Windermere Basin where channel erosion effects would be minimized.
Design criteria for the long-term success of the channel were also provided to other consultants so that stream design constraints could be integrated into in their respective assessments and designs. These criteria included: •
Bridge spans for C-type streams should be no less than a 24m clear span width for arterial and expressway bridge crossings unless alternative mitigating techniques can be applied. Bridge piers would not be permitted within the bankfull channel limits, and the bed material and cross-sectional profile underneath any structures constructed would conform to natural channel design principles. Pedestrian, golf course and maintenance bridges could use a smaller clear span (bankfull width plus 2m beyond each side of the bankfull channel) criteria providing that ramp-up’s to both sides of the bridges were not in-filled (i.e. clear span) so that velocity distributions of the bankfull and floodplain flows would not be altered,
•
Bridge spans for B-type streams should be no less than 18m in spanning width unless alternative mitigating techniques can be applied. Bridge piers would not be permitted within the creek channel, and the bed material and cross-sectional profile underneath any structures constructed would conform to natural channel design principles. Pedestrian, golf course and maintenance bridges could use a smaller clear span (bankfull width plus 2m beyond each side of the bankfull channel) criteria providing that ramp-up’s to both sides of the bridges were not in-filled (i.e. clear span) so that velocity distributions of the bankfull and floodplain flows would not be altered,
•
Top width and cross-sectional profiles for the various stream morphologies were provided for cut/fill exercises to determine the net material balance of the natural channel works. Also from the cut/fill exercises, the limits of grading and terrestrial impacts could be determined,
•
Locations for increased plantings where high rooting densities are required to maintain stream stability along the length of the proposed stream alignment were provided to the terrestrial biologists and landscape architects for integration into their design plans,
•
No on-line stormwater quality / quantity facilities throughout the entire length of the natural channel design corridor of the main branch of Red Hill Creek would be permitted. Stormwater quantity facilities must be off-line and discharge back to the stream channel on the inside lower third of meander
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bends, •
The off-line storm water quantity facility in the Rosedale baseball diamond area will maintain a berm height such that the spill into the storm water quantity facility will not occur until a return period greater than the annual return frequency (20 m3/s - 24 m3/s). This criteria will maintain sediment routing of the channel through a designed valley corridor and sustain the long-term stability of the channel,
•
Storm sewer pipe discharges from the expressway must first settle in dissipater ponds. Moreover, storm water flow must confluence with the stream restoration on the inside of the bottom third of any bend proximal to the storm sewer outfall,
•
Any existing storm, sanitary or trunk sewers passing across the bankfull channel limits must comply with natural channel design principles. Therefore, the base of the stream must be constructed out of natural materials (existing substrate) without any fortification (i.e. hardening of the stream bed through the use of concrete, rip-rap, gabions or armour stone revetments). Infrastructure would be located to cross the stream at the upper margins of riffles where in-stream structures could be used to mitigate any down-cutting of the stream and provide stability for the underlying infrastructure.
3.1.2 Design Dimensions, Patterns and Profiles Four cross-sectional channel forms have been developed to address the two different stream morphologies proposed for this rehabilitation plan in addition to the two bankfull regimes that exist. C-type and B-type bankfull and flood prone cross-sectional profiles have been developed for the reaches up-stream of the Davis Creek / Montgomery Creek confluences with a design bankfull discharge of 9.5m3/s. The second set of cross-sectional forms are developed for the areas downstream of the Davis Creek / Montgomery Creek confluences with a bankfull discharge of 12.0 m3/s. The design flow for this reach was derived from the sediment transport studies described in Section 1.3.7 (Figure 1-33) which identified that between 9.5m3/s and 13m3/s was the discharge of the channel most affecting sediment transport. Transport of the coarsest size fractions occurred between 11 m3/s and 13 m3/s. Therefore, this is the morphological forming flow that maintains the greatest stability in channel dimension, pattern and profile over the long-term. Frequency of overbank flow, by virtue of the change in invert elevation of the proposed channel, must also increase in the post-design period. As illustrated in Figure 3-2, the invert elevation of the channel will, in most instances, be elevated above the existing channel bed. This design objective is to ensure that as soon as bankfull flow is exceeded (in the C-type streams) water will begin to inundate the flood plain. This discharge stage relationship decreases mean channel velocity above bankfull flow and minimizes in-channel erosion. The velocity distribution as a function of flow is illustrated in Figure 3-3 and graphically Figure 3-4. The velocity distribution requirement for the pool-riffle flood plain dominated morphology (i.e. C-type) provides the hydraulic function to sustain Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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Figu re 3-2
Flood p lain access for pr oposed str eam restoration
Figu re 3-3 Mean channel velocity distributions for bankfull and flood flow
Figure 3-4
Discharge vs. mean channel flow velocity for C-type stream
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a stable cross-sectional form. In the flood plain channel morphology, the velocity distribution will produce the minimum channel shear stress and hence lowest rates of channel erosion. The frequency of over bank flooding where the B-type stream morphologies are proposed is less than in areas dominated by the C-type stream. This is by virtue of the B-type stream morphology which requires moderate entrenchment to remain stable. This stream morphology, however, is only stable in steeper gradient reaches (i.e. within and south of the golf course) or for short distances where channel encroachments existed in low gradient portions of the stream (i.e. up-stream of the TH&B railway and under the Queenston Ave. bridge). Elsewhere with low gradient conditions, the B-Type stream morphology would not have sufficient gradient and plan form sinuosity to dissipate the energy conveyed within the channel, creating a condition which typically results in accelerated rates of channel erosion. In the areas dominated by the B-type morphologies, the frequency of flooding to the flood plain should essentially remain unchanged or decrease, with flooding occurring on average one to two times per year. In some areas, for instance near fairway 11 on the Kings Forest golf course or upstream towards the Bruce Trail foot bridge, increased flooding will occur. Presently, the highest flow stage of this reach never exceeds a stage beyond the tops of its banks (see Philips Engineering, 2002). This is a function of the entrenched state of the channel and is one of the primary reasons for the present degraded state of the channel. The proposed rehabilitated reach in this area (B-type stream) will not begin to flood onto the flood plain until an approximate 20-year return period has been exceeded (a natural channel design constraint). For the full range in flood regimes, refer to the flood plain hydraulics report of Philips Engineering, 2002. Based upon meeting all of the impact and design constraints outlined in Section 2, a plan form of the channel was developed. However, the design layout was an iterative approach since the crosssectional form of the channel was designed first, resulting in a distinct suite of plan form parameters used to develop the plan form meander geometry. The basic criteria in developing the plan profile was to minimize cut and fill requirements and terrestrial impacts and develop a geometric profile that (derived from the cross sectional form) conveyed the current and future sediment and flow regimes. As outlined in Figures 3-13a - 3-13e of Section 3.2, several stream gradients were possible for each proposed reach. The steepest and shallowest gradients will be outlined in the design relationships as they represent the limits of the design parameters. Based upon the existing conditions (Section 1.0) and relationships described by Annable [1996], the natural channel parameters are outlined in Tables 3-1 - 3-4. As mentioned above, four stream designs are reflected in Tables 3-1 - 3-4 to account for the two different stream morphologies (i.e. C-type and B-type streams) and the two different morphological forming flows upstream and downstream of the Davis Creek confluence. Within each of these tables, attention is directed at the ranges in design parameters, particularly for meander wave length , meander amplitude, and radii of curvature. The variation in these parameters provides the limits in modifying the plan form meander geometry in order to meet the design criteria and minimize as many of the impacts discussed in Section 2.0 as were feasible. The meander geometry of the channel was derived from the relationships developed by Annable [1996] for streams in southern Ontario and meander geometry measured by Annable [1995b] for Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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the reach between Queenston Ave. and Melvin St. were also used. As outlined in Section 1.3.7, the reach between Queenston Ave. and Melvin St. is presently experiencing the lowest rates of channel erosion and would be the most representative of the stable plan form geometry of the watershed. These values are compared and weighted against general relationships offered by Annable [1996] with respect to the unique geology and flow regime of the watershed. Table 3- 1
Detailed natural channel design parameters for Ctype stream downstream of Davis Creek confluence
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Table 3- 1cont.
Detailed natural channel design parameters for C-typ stream downstream of Davis Creek confluence
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Table 3- 2
Detailed natural channel design parameters for Ctype stream upstream of Davis Creek confluence
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Table 3- 2cont.
Detailed natural channel design parameters for C-type stream upstream of Davis Creek confluence
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Table 3- 3
Detailed natural channel design parameters for Btype stream downstream of Davis Creek confluence
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Table 3- 4
Detailed natural channel design parameters for Btype stream upstream of Davis Creek confluence
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3.1.2.1 Depth to Bedrock As outlined in Section 1.0, where the stream flows over bedrock or in close proximity to this surface, higher rates of stream bank erosion are observed. A design objective was to ensure that the preferred alignment was as far away from bedrock as possible to minimize lateral migration of the stream and to provide the greatest diversity in in-stream physical habitat Also, eliminating or reducing the amount of the creek that flowed over bedrock would reduce the potential for stream entrenchment which presently occurs within several reaches of the longitudinal profile of the channel. A review of existing borehole logs within the lower valley was undertaken to determine depth to bedrock. However, when this information was collated with the existing outcrop locations along the valley and locations where the stream flowed over bedrock, there was insufficient information to develop a bedrock contour map with sufficient accuracy to meet the design analysis criteria. Therefore, an additional 149 boreholes were drilled within the lower valley along various proposed creek alignments to determine the depth to bedrock. The location of the boreholes are illustrated in Figure 3-5 and the detailed borehole log inventory included in Appendix V. As part of the plan form design, the meander geometry of the stream was moved, wherever possible, to increase the depth to bedrock. Potential alterations in the plan form alignment were achieved by developing and utilizing an isopac map (ground surface elevation minus the bedrock surface elevation), as illustrated in Figure 3-6 (which may also be included in the distribution of this document as a drawing insert), to evaluate overburden depths. The various stream alignments were then superimposed upon the isopac map. Where opportunities existed to move the channel within the existing constraint, and within the range in meander geometry design parameters to increase depth to bedrock, the alignment was altered accordingly. The preferred depth to bedrock criteria was a depth greater than three times the bankfull depth of the channel above the bedrock surface. This criteria would ensure that bedrock control of the stream would be minimized. 3.1.3 In-stream Structures The natural channel design approach not only relies upon the proper dimensions, patterns and profile of the stream in balance with the existing land use and sediment regime but also on in-stream structures to mitigate much of the near bank shear stress. The placement of structures also enhances the success rates of riparian plantings along the banks of the stream since erosion rates are reduced and plant material have longer time spans to develop dense stable rooting systems. A series of in-stream structures are used throughout the proposed design which have been proven stable over time through continued monitoring of previous restoration projects. Figures 3-7 through 3-10 outline the various structures which will be employed in this restoration. The primary function of these structures is to decrease near bank shear stress and/or to maintain grade control to assist in sustaining the stable dimension, pattern and profile of the proposed alignment. As part of the emergency works construction in 2000 to mitigate a failed channel section beside fairway 11 of the Kings Forest golf course, cross vane structures were installed to maintain grade control through this reach. Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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Figu re 3-5 Boreh ole in vent or y lo catio ns with in t he lo wer valley Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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Figu re 3-6 Red H ill C reek valley isopac m ap Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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Figure 3-7
Rock vane in-stream structure
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Figure 3-8 J-hook vane in-stream structure
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Figure 3-9 Root wad in-stream structure
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Figure 3-10 Cross vane in-stream structure
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Since the installation of the three structures in the spring of 2000, an as-built and two subsequent monitoring surveys have been conducted in May 2000, June 2001 and May of 2002 respectively, to demonstrate the reliability of NCD structures in maintaining channel stability. The location of the structures and monitoring survey results are presented in Figures 3-11 and 3-12 respectively. Between the construction of the in-stream structures in the spring of 2000 and the monitoring survey in May of 2002, the reach has experienced 14 flow events exceeding bankfull discharge (9.4 m3/s) with the largest flow event occurring in 2001 at 21.28 m3/s which equates to the 5-year return
Figu re 3-11 In-str eam stru cture m on ito rin g section s at Red H ill Cr eek - Fairway 11 - Kings Forest golf course
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golf course.
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period. As illustrated in Figure 3-12 the cross-sections and longitudinal profile of the reach have essentially remained unchanged. There are minor amounts of aggradation occurring in localized sections which are coincident with the pool locations, however, these occurrences are cyclic with the varying flow conditions meaning that they would be expected to scour out in certain storms. Since the channel above the re-constructed reach is still fully entrenched with high rates of bank erosion, a certain degree of aggradation should be anticipated within the re-constructed reach. The re-constructed reach has a wider cross-sectional profile with decreased side slopes approaching the stable form of the appropriate step-pool morphology for this region (B-type stream). Thus, the reconstructed reach with the broadened cross-sectional profile, relative to the upstream entrenched reach, decreases stream power and the capacity to carry the coarsest material which results in the increased potential for aggradation to occur. However, the critical observation from the monitoring results of Figure 3-12 is that when the channel profile is designed and constructed in consideration of the stable morphological regime of the channel and in-stream structures are introduced to further mitigate grade control and bank erosion, a stable channel results which does not require further erosion control measures. 3.2 Preliminary Natural Channel Design After the information gained from existing conditions (Section 1) was combined with the various constraints and impact assessments of Section 2, a preferred alignment was developed. The preliminary design is illustrated in Figures 3-13a - 3-13e. Depending upon circulation of this document, a additional roll-out drawing may be provided at a scale of 1:2000 (not intended for construction purposes). The preliminary design outlines the final proposed creek alignment with the number and discrete locations of in-stream structures specified, reach based stream gradients, stream morphologies and thalweg profile (including riffle and pool depths). Also included in the preliminary design drawings are the detailed stream design drawings for the erosion control and leachate management works (Dillon, 2001) which are occurring in 2002 down stream of the CNR railway which were designed by Water Regime Investigations and Simulations Ltd. The Rennie St. detail drawings have been incorporated into the balance of the preliminary design drawings as they will represent the “current channel alignment” considered within this document and all future rehabilitation projects. Moreover, the incorporated detailed drawings provide the reader with an appreciation for the level of detail that will be incorporated into any final creek detail design drawings that are produced. In general, from preliminary to detailed design drawings, discrete construction elevations are specified on each in-stream structure, as are the invert elevations of pools and the lead end of riffles. Construction materials, salvage material, substrate sizes and their distribution are further specified for tendering purposes in final design drawings. The natural channel design extends from the Bruce Trail foot bridge to approximately 400m down stream of the CNR and has a total length of 7,607m. This proposed reach is 328m longer than the existing stream (7,279m) within the same area. Table 3-5 summarizes stream types and lengths proposed in addition to the number of pools, riffles and in-stream structures. For comparison purposes, the existing lengths of various stream types and morphological features are included. As evidenced in Table 3-5, the proposed natural channel design does not have any entrenched (FPreliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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type) stream channels. An F-type morphology is an expression of a degradational phase of a channels evolutionary cycle, for the given geology, and was not a desired design objective. Table 3-5 Comparison of stream morphologies and in-stream structures Stream Morphology / Feature
Existing Alignment
New Alignment
Length B-type stream (m)
598
2296
Length C-type stream (m)
5855
5311
Length F-type stream (m)
826
0
Pools
60
125
1.25 (F2 =0.4)
2.5 (F2 = 0.5)
Riffles
54
68
Steps
4
56
Pool Depth (relative to bankfull depth)
Rock Vanes
73
J-Hooks
50
Root Wads
41
Cross-vanes
128
Length of stream covered by bridges (m)
338
563
The particle size distribution of substrate throughout the proposed alignment will be the same as presently found in the creek, as outlined in Figure 1-37. The particle size distribution which will be used in the restoration is d 16=22mm, d50=82mm and d84=105mm. Every effort shall be taken to salvage existing material within the existing creek bed as phasing of the construction permits, as outlined in Section 3.5. As indicated in the preliminary design drawings and Table 3-5, additional structures will be used in the stream to maintain or reduce stream channel erosion. In addition, sod mats and plantings will also be placed along the stream banks to minimize bank erosion through vegetative control (bioengineering). Table 3-6 outlines the anticipated quantities to construct the various in-stream structures or to augment the banks with vegetative control. A cut and fill analysis was also undertaken along the centre line of the proposed alignment using the cross-sectional criteria outlined in Figures 3-14 - 3-16. The bankfull profile was superimposed using the above cross-sectional criteria on a digital terrain model developed for the valley and quantities were calculated by Philips Engineering. Results of this analysis determined that 144,000 m3 of excavation and 31,000m3 of fill would be required to produced the stable natural channel form. The limits of excavation are also illustrated in Figures 3-13a - 3-13e. Surplus excavated material will be used to in-fill portions of the existing channel where wetlands, ponds or stormwater quantity and Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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quality facilities are not proposed once portions of the stream have been taken off-line and the present substrate removed (see section 3.5). The backfilling of the existing stream channel will assure that the proposed alignment is one of the lowest points within the valley and that future stream capture back to the existing channel will be minimized. It should further be noted that only portions of the existing channel on the west side of the proposed expressway would require in-filling (with the exception of the reach down stream of Barton St.). Thus the remaining channel portions that are on the opposite side of the expressway can be used as storm water quality/ quantity facilities or for developing oxbow wetland areas. Table 3-6. Stream restoration materials requirements
3,271
1,880
1m x 0.75m x 0.75m armour stone
209
104
1,126
1,439
827
104
282
386
401
418
362
1,690
2,470
8,673
314
155
844
1,401
11,667
1.25m dia boulders (round to sub-rounded)
104
52
282
438
7,119
1.5m dia boulders (round to sub-rounded)
104
52
282
438
12,301
0.5m dia boulders (round to sub-rounded) 0.75m dia boulders (round to sub-rounded) 1.0m dia boulders (round to sub-rounded)
88
0.3m> dia footer logs (4m-5m long)
47
47
0.4m> dia deflector logs (root mass > 2.5m dia) (4m-5m log)
47
47
)
1,972
Total linear (m)
672
Tonnage
Cross vanes
627
Total number
J-hook vanes
1m x 0.5m x 0.5m armour stone
Root W ads
Rock vanes
Units of Material
Sod mats 3m deep on bends with 1.5m centre on shrub plantings such as dog woods, wild rose, hawthorn etc. to maximize rooting density (minimum requirements). Material sourced from salvage withing the existing corridor if possible.
4,700
14,100
Sod mats 3m deep on riffles (minimum requirements) Preferable if the sod mats could be salvaged through the grubbing process on site for the expressway to maintain local soil conditions and reduce mortality.
3,800
11,400
Commensurate with the re-alignment of the channel and the cut and fill requirements, terrestrial losses will also occur. The cut and fill limits were provided to Dougan and Associates and the Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
Cut and fill cross-sectional template for C-type stream morphology on riffles
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Cut and fill cross-sectional template for C-type stream morphology on bends
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Cut and fill cross-sectional template for B-type stream morphology on riffles
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terrestrial resources within this corridor calculated. The results of this assessment are outlined in Table 3-7. The limits of calculation assumed an additional 3.5m wide buffer beyond the cut / fill limits for a working easement. For further impact assessment with respect to the terrestrial resources, refer the impact report of Dougan and Associates [2002]. Table 3-7. Terrestrial losses from natural channel design(Dougan and Assoc., 2002) Terrestrial Community
Hectares Lost
Anthropogenic Open Space (recreational areas, lawns, formal landscaping)
4.1
Anthropogenic Woodland/Forest (maintained ornamental landscaping)
1.3
Natural woodland/Forest
12.5
Secessional (shrub thicket, old fields)
2.7
Wetland (cattail marsh)
0.4
With the change in cross-sectional form of the channel to re-establish the bankfull channel with the flood plain (in the C-type streams) as discussed in Section 3.1.2, there will be increased frequency of inundation into the flood plain. This will be commensurate with each event that exceeds bankfull discharge. Therefore, in the C-type stream morphologies proposed up-stream of the Davis / Montgomery Creek confluences, flooding into the flood plain will begin to occur, on average, six times per year. This will increase from the current average of once per year as discussed in Section 1.3.3. For the reaches downstream of the Davis / Montgomery Creek confluences, inundation of the flood plain will begin to occur, on average, nine times per year. This is an increase in frequency from the present four times per year, on average, as discussed in Section 1.3.3. From the longitudinal profiles presented in Figures 3-13a - 3-13e, bedrock will intercept the bottom of the proposed stream invert for approximate 340m of the entire length of the rehabilitated stream. This will be a reduction in current length directly over bedrock of approximately 1700m. Also outlined in Table 3-5, the length of stream passing under bridges will increase from the present 338m to 563m. The number of bridges increase from the present 14 to 22. The length of stream inventoried for existing conditions considered all bridges between the Bruce Trail foot bridge (southern limit) and 400m down stream of the CNR railway bridge (northern limit). Bridges included in this inventory, as discussed in Section 1.3.7, included rail lines, expressway crossings, arterial roadways, pedestrian, maintenance, golf cart and emergency access bridges along the centre line of the bankfull channel. The inventory of the proposed alignment included the infrastructure that would remain after rehabilitation in addition to the two expressway crossings (upstream and down stream of the CNR railway), on and off ramps and pedestrian / emergency access / maintenance bridges. Assumptions were made with respect to the number of bridges for pedestrian crossings, golf carts and maintenance/emergency access bridges as they were not finalized at the time of this report. Numbers were based upon assuming a continued pathway throughout the valley and replacement of the existing number of emergency access/ maintenance bridges and one golf cart bridge for each fairway crossing. The various additional bridges assumed as part of the bridge network inventory are outlined in Table 3-6. It should be further noted that in addition to the various bridges that will be relocated, there will be the elimination of the stream crossing at Melvin Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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St. as this roadway will be eliminated over the valley.
Table 3-8.
Estimated Additional bridges for stream coverage by structures estimation Number of bridges assumed
Width of bridge(m)
Maintenance / Emergency Access
1
8
Golf cart
4
2
Pedestrian
4
3
3.3 Sediment Loading A sediment loading analysis was undertaken for the proposed natural channel design reach to determine loadings to the creek. The calculation method is similar to that used in Section 1.3.6. However, rather than using the field measured erosion rates for the existing channel, field monitored erosion rates from previously constructed in-stream structures (Figures 3-7 - 3-10) on other streams projects were used. The average erosion rates of constructed in-stream structures observed through ongoing monitoring from other restoration projects is typically less than 0.01m/year. Using this value as the upper limit of erosion rates and substituting this value into Equation 2, a net total of 205 tonnes/year would contribute to the stream after the restoration works have been completed. This calculation further assumes that the average bank height on each bend is 2.25 m in the C-type streams and 1.75m in the B-type streams which are the mean design bank heights from the invert of the pool to the top of bank. The 0.01m/year erosion rate is considered, from previously monitored projects, to be an upper limits of erosion rates observed producing a conservatively high sediment loading estimate. The bulk density used was 1920 kg/m3 which is typical of the alluvial deposits found throughout the valley (Appendix 7). Comparing the existing reach from the Bruce Trail foot bridge (most upper limit of the proposed restoration channel) to 400m down stream of the CNR (the same limits compared as in the existing conditions of Section 1.3.6) the sediment loading would decrease in this reach from approximately 3,400 tonnes/year to approximately 205 tonnes/year. The differences in sediment loadings (pre and post restoration) are illustrated in Figure 3-17. The existing sediment loading plot combines the measured and inventoried erosion rates of each bend within the project limits and the down cutting rates observed from as-built comparisons of structures within the valley as discussed in Section 1.3.6. In previous restoration projects on similar geology, slope and watershed land use, an even lower average bank erosion rate of 0.005m/y is commonly observed. If this erosion rate were applied to the above analysis, an annually loading of 102 tonnes/year may be expected. Regardless of which post-construction erosion rate is used, the proposed stream restoration would cause a significant reduction in sediment loadings to the stream and finally to Windermere Basin. It is more Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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appropriate to evaluate the potential ranges in sediment loading to the stream from future constructions with the present rate of sediment loading to the stream to gain a general appreciation for the magnitude in reduction of sediment loading to the stream. Therefore, if the average sediment loading, as discussed in Section 1.4.5, of 7,750 tonnes/year were used that discharges into Red Hill Marsh (prior to the sewage treatment plant discharge) and the existing sediment loading to the stream were reduced from the existing 3,400 tonnes/ year to the range of 102 tonnes/year to 205 tonnes/year, the sediment loading to Red Hill Marsh would be reduced by approximately 4,452 tonnes/ year to 4,555 tonnes/year. This reduction in sediment loadings equates to an approximate 43% reduction in sediment loadings to the Red Hill Marsh per annum.
Figure 3-17
Comparison of sediment loadings to Red Hill Creek from pre to post stream restoration.
3.4 Contractor Selection As mentioned in Section 1.5, specialized construction experience is required in properly constructing a natural channel design. The handling of plantings, placement of structures, trained personnel and the site management practices can dictate the success of a restoration project as much as the proper design. Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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It is recommended that to minimize design risk and maximize long-term stability of the channel, a contractor experienced in constructing the proposed in-stream structures be retained without implementing the tendering process. Selection of an appropriate contractor is recommended through a pre-qualification involving panel screening between the stream restoration design engineer, terrestrial biologist, design engineer, landscape architect and applicable City staff. The following are the recommended criteria for screening and selection of the appropriate contractor: •
Request a portfolio of completed stream rehabilitation projects which includes: pictures of pre-, during-, and post-construction. The pre- and post-pictures provide visual information on the visual quality of the work. Pictures during construction are of benefit to determine the work ethic of the contractor and their ability to environmentally manage a site.
•
The length of each stream constructed, average cost per unit length, percent hold-back, duration of hold-back, whether the project was a tender or rate pay contract, time to completion, previous success and the number of trained personnel.
•
Request contact numbers of the previous stream rehabilitation designers who the contractor has worked with, to ascertain the quality of work of the contractor, field co-operation, and to obtain monitoring information about the long-term stability of each project (experienced contractors should have this information available).
•
Require that a contractor cannot sub-contract the job after it has been awarded. The construction must be done exclusively by the contractor selected.
•
Obtain a listing of plant materials that the contractor is familiar with, the range in caliper of tree that they are experienced working with and mortality rate after planting. Mortality estimates can usually be obtained from monitoring or hold back summary reports by the consultant responsible for the design if a specific contractor does not have them.
•
Require a listing of structures constructed, and how many projects they have been used on from each contractor. For example Table 3-9 outlines an inventory list that each bidding candidate should complete that outlines the streams that have been worked on, the types of in-stream structures built. This demonstrates the firm’s relative experience. The retained contractor must have experience with the in-stream structures shaded in this table to be a candidate for selection.
Hold-backs should also be incorporated into the construction contract. Since most of the materials used in a natural channel design are native materials (rocks, logs etc.), subtle adjustments are required after construction that require attention to eliminate localized areas of adverse erosion that Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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can not be fully realized at the time of initial construction (i.e. the requirement for a high flow event). Often, the placement of a given boulder with a given shape may produce undesirable convergent or divergent flow patterns that may cause back eddies, hydraulic jumps, or convergent flow resulting in adversely high erosion. The contractor must return to the field with the designer to alter the positions or replace rocks and structures if required. If all of the structures were properly designed and constructed initially, these ‘fine tuning’ events occur only in the first one to two years after construction and should be anticipated.
Stream
Stream Length (m)
Armor stone
Rip-rap
Gabions
Rocky - Ramps
Lunker Units
Wing Deflectors
Boulder Placements
Riffles
Pools
Roller Logs
Rock Vanes
Log Vanes
Cross Vanes
Vortex Rock Weirs
Double Wing Deflectors
Table 3-9. Contractor in-stream construction survey
A
495
U
U
U
U
U
!
"
U
U
"
"
!
!
X
!
B
654
U
U
U
!
!
X
!
!
!
!
!
!
!
X
!
C
1112
U
U
U
!
!
U
"
U
U
U
U
"
"
U
"
NOTE: U - excellent success, "- moderate success, ! - have not constructed, X - poor success
Dependent upon antecedent moisture conditions, the timing of construction and seasonal weather patterns, mortality rates of transplanted vegetation can be high. In many instances, this can be offset by utilizing a diversity of plantings along each bend rather than homogeneous planting of species. In the event that high mortality rates occur and re-vegetation of failed areas is not quickly implemented, long-term integrity of the channel is in jeopardy and liability significantly increased. Although this is a random consequence of nature that is not attributable to the stream channel design, bio-engineering or the contractor, remedial measures must be undertaken to maintain the long-term stability of a given project. Therefore, these contingencies must be built into a representative hold-back for the first two years after the completion of the project.
3.5 Construction Phasing of the Stream Corridor Much of the proposed natural channel design is in a different location than the existing stream. This provides an opportunity for a large portion of the channel to be constructed in the dry, off-line of the existing flow. This opportunity will reduce the need for in-stream erosion works and decrease construction expense. The linear expanse of the stream restoration project provides several opportunities for construction phasing to ensure that works would not be undertaken in the channel during any fish migratory periods. Moreover, bulk stream channel excavation away from the current flowing channel could be undertaken at anytime of the year. Therefore, phasing of plantings could be coordinated such that installation of sod mats, transplants, etc. can be undertaken at the best time of the year (i.e. spring and fall) to minimize mortality rates. The channel can be constructed and left without Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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implementing rigorous plantings until the optimal times of the year for planting have arrived. Reach specific phasing will depend upon supply and demand of material within the creek and the expressway project (i.e. armour stone source, source for sod mats and root wads etc). However, there are many areas associated with expressway crossings and / or on/off ramps where general construction practices and the stream restoration will overlap. To minimize the impacts to the stream restoration and perturbations to any of the structures built, and/or to minimize duplication of in-stream works, it is recommended that creek spanning structures be built prior to the stream rehabilitation wherever possible. This phasing would minimize impacts to the rehabilitated creek. In-filling of the existing reaches would occur after new portions of the channel become activated to circumvent the existing flow route. However, before in-filling of the abandoned channel occurs, it is recommended that excavation of the existing channel substrate be undertaken to an approximate depth of 0.5m (the typical shear depth / depositional depth of stream deposits). This salvaged material would be used in the proposed channel to replace the substrate through the riffles and on the point bars, thus providing the proper grain size distribution / substrate to the new channel to establish the functional sediment transport processes. The majority of this material would then provide the basis for in-stream substrate. Regardless of the overall phasing of the project, it is strongly recommended that rehabilitation of the reach between the Bruce Trail foot bridge and approximately the Greenhill CSO be conducted first. As discussed in Section 1.0, this portion of the stream is highly incised and experiences very high rates of erosion. Stabilizing this reach would reduce sediment delivery to down stream reaches, reduce stream power and eliminate on-going capital costs for maintenance of erosion control structures throughout the Kings Forest golf course. Stabilization of this reach, which is the highest gradient component of the entire valley, would also begin to reduce the rates of stream channel erosion currently observed in down stream reaches. As a result, down stream reaches that would be rehabilitated would not have to have to respond to any adverse sediment loading regimes from bank / bed erosion potentially requiring interim maintenance.
3.6 Site Inspection Site inspection for the stream restoration component of this project should be carried out by experienced stream restoration personnel. A full time presence during construction when operators are on site should be maintained. Inspectors should provide guidance and design specifications to the contractor on the proper methods of in-stream structure construction, location of plantings, grading and general site management. Also, stream restoration supervision staff should participate with the terrestrial biologists, landscape architects and the contractor in selecting the various materials required for the stream rehabilitation. Specifically, the species and sizes of trees that will be salvaged for root wads, sod mats and transplants will be coordinated. Similarly, selection of boulders an/or armour stone will also be coordinated with the contractor to ensure that the proper boulder sizes and shapes are obtained.
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3.7 Monitoring A monitoring program is proposed throughout the entire rehabilitated reach to quantify the stability of the stream restoration program. In addition, the level of monitoring proposed would quantify the sediment loading to the stream throughout the rehabilitated reach and provide information on the volumes of sediment passing through the creek and being delivered to Red Hill Marsh. Through the construction of the proposed natural channel design, the existing Environment Canada Gauge station at Queenston Ave. will be abandoned as the channel will have moved from the present location to the west side of the valley. It is recommended that the gauge station be relocated to continue monitoring the flow characteristics of the creek. In addition, the current suspended sediment monitoring program is recommended to be continued at the re-located gauge station. Since there is a significant reduction in sediment loading predicted from the stream restoration, these results should be verified from the flow and suspended sediment monitoring program. Moreover, information gained from this monitoring exercise will not only assist in validating the performance of the restoration works within this watershed but will also provide design guidance and validate a method of significantly reducing sediment loadings to streams that can be applied to other watersheds. To capture the largest portion of the rehabilitated reach, for both flow and sediment transport, it is recommended that the present Queenston Ave. gauge station be re-located to a location in the vicinity of the Barton St. bridge. This location is the furthest downstream point above the backwater effects of Lake Ontario. Therefore, it would be the most suitable location to capture the largest portion of the watershed flow and suspended sediment transport. The continued operation of the Mount Albion gauge station and suspended sediment monitoring program is also recommended. If additional suspended sediment samples can be collected at a broad range of flows, particularly at high flows, a more reliable suspended sediment rating curve can be developed to evaluate the watershed sediment budget from above the escarpment. Then, a mass balance analysis can be accomplished between the Mount Albion gauge and the newly located gauge at Barton St. and sediment loading from the rehabilitated reach ascertained. A new and third flow and suspended monitoring station is proposed within the watershed at a point downstream of the new CSO discharge confluence and up-stream of the Davis / Montgomery Creek confluences. Flow and suspended sediment information obtained from this station would provide a detailed base line for a sediment mass balance assessment determining the sediment loading to the creek and verifying the rates of bank erosion. Moreover, a gauge station within this reach would verify the proper functioning of the re-configured CSO facility and assist in corroborating the monitoring exercises proposed below to document the efficiency of the various in-stream structures. In addition to monitoring the flow and suspended sediment characteristics of the rehabilitated reach, a series of monitoring stations and erosion sections are proposed to evaluate the long-term stability of the channel. Information gained from these monitoring surveys will not only provide fundamental information on validating the success of the restoration, but will also provide future guidance to other stream restoration projects on the functioning of the various in-stream structures Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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either on the Red Hill Creek watershed or elsewhere. Moreover, if areas of instability are observed, the monitoring program can then be used to implement recommendations for in-stream works to resolve reach issues. Since the scale of this project is, on average, longer than many other continuous urban stream rehabilitations undertaken in Ontario, additional tasks in addition to the standard stream monitoring program are recommended to ensure that thorough evaluation of the restored reach is achieved. The following is a listing of the proposed monitoring tasks (additional tasks unique to this project have been underlined): •
Conduct a longitudinal profile survey once a year, on or about the same date, for each of the first five years after construction, the tenth year after construction and once after a significant discharge event (greater than 25 year storm). Each monitoring survey should include the locations of the deepest points in the pools, tops and bottoms of riffles and sufficient detail to represent the profile of the reach. A rule of thumb that will be followed is one discrete survey point as a minimum every channel width along the center line of the surveyed reach. A consistent stationing (chainage) should be used so that, as the monitoring program continues, the longitudinal profiles can be superimposed upon the same plot for comparison.
•
Install permanent cross-sections on the bottom third of approximately 1/5 of the bends within the rehabilitated reach (approximately 18 of the 91 bends) and on the top third of approximately 15 of the 68 proposed riffles to monitor channel stability. Each cross-section would establish a consistent chainage protocol so that, as the monitoring program continues, plots of consecutive cross-sections at each monitoring station can be superimposed for comparison. A minimum of fifteen discrete survey points are recommended along each cross-section which includes the locations of: the deepest point of the channel, bottom of bank, top of bank, bankfull stage on the left and right banks. Additional survey points should be obtained to characterize the bed of the contemporary channel This information will used to determine the rate of migration of the outside of the bend (on bend cross sections), changes in bed elevation for both the bend and riffle sections and document the changes in cross-sectional area to determine if quasi-equilibrium is established in the channel. A sub-set of monitoring sections will be placed upstream and downstream of the in-stream structures to verify their stability and hydraulic function.
•
At the same locations as the permanent cross-sections on riffles, pebble counts should be conducted (no less than 100 pebbles per section). This monitoring survey would enable changes in substrate distribution to be observed over time. The analysis should include a single grain size analysis plot for each cross-section and superimposed in consecutive years of monitoring. Also the d5, d16, d25, d50, d75, d84, d95 particle sizes will also be documented for each analysis.
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•
A photographic monitoring program should also be implemented. Photographs should be taken at exactly the same locations over the period of the monitoring program. It is recommended that photographs be taken at the permanent cross sections on the outsides of bends with views upstream and downstream. In addition before construction commences, during and for each year after for the first five years of post-construction, an aerial video taping should be conducted to document the progression of the channel construction and the terrestrial responses after construction. Also, if a significant return period occurs, an aerial video taping should also be conducted to document the channels location and stability after such an event.
A annual monitoring report should be developed which documents the above information and identifies locations where channel stability is being maintained and where channel migration is being observed for each cross section and the longitudinal profile. This summary should also document if any changes in substrate distribution are occurring over time as determined from the pebble counts. Also, the summary should indicate any locations along the length of the channel that are failing and the magnitude of failure with proposed intervention strategies.
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REFERENCES ANDREWS, E.D. and J.M. NANKERVIS, 1995, Effective discharge and the design of channel maintenance flows for gravel-bed rivers, In “Natural and Anthropogenic Influences in Fluvial Geomorphology”, Eds. J.E. Costa, A.J. Miller, W. Potter and P.R. Wilcock, Geophysical Monograph 89, pp. 151 -164, ISBN # 0-87590-046-1. ANDREWS, E.D., 1984, Bed-material entrainment and hydraulic geometry of gravel-bed rivers in Colorado, Geological Society of America Bulletin, Vol. 95, pp. 371 - 378. ANNABLE, W.K., 1999, On the design of natural channels: decisions, direction and design, Presented at the Natural Channels Systems Conference, March 1 - 4, 1999, Niagara Falls, Ontario, Canada, pp. 27. ANNABLE, W.K., 1996a, Morphologic relationships of rural watercourses in southern Ontario and Selected field methods in fluvial geomorphology., Ontario Ministry of Natural Resources, ISBN# 0-77785113-X, pp. 92. ANNABLE, W.K., 1996b, Database of morphologic characteristics of watercourses in southern Ontario, Ontario Ministry of Natural Resources, ISBN# 0-7778-5112-1, pp. 212. ANNABLE, W.K., 1995a, Morphologic relationships of rural watercourses in southern Ontario for use in natural channel designs., M.Sc. Thesis, School of Engineering, University of Guelph, Guelph, Ontario, Canada, pp. 377. ANNABLE, W.K., 1995b, Database of morphologic characteristics of urban streams in southern Ontario, Ontario Ministry of Natural Resources, Interim Report BRUNNER, D.S., 1999, Methods for estimating bankfull discharge in gauged and ungauged urban streams, B.Sc. Thesis, Department of Earth Sciences, University of Waterloo. DICRESCENZO,R., D. HATANAKA, W. LEE, 1996, Fluvial geomorphology study of Red Hill Creek, B.A. Theses, Department of Geography, McMaster University, Hamilton, Ontario, Canada ENVIRONMENT CANADA, 1990, Fifteen minute stage/discharge data: Gauge 02HA014 (Red Hill Creek at Hamilton), Environment Canada, Monitoring and systems branch, Guelph, Ontario. ENVIRONMENT CANADA, 1990, HYDAT CD_ROM Ver. 3.0, Water resources branch, Inland Water Directorate, Environment Canada, Ottawa, Ontario. FERKO, D, 2000, Erosion characteristics of Red Hill Creek, Unpublished M.Sc. Thesis manuscript, School of Engineering, University of Guelph. Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.
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FISRWG, 1988. Stream Corridor Restoration: Principles, Processes, and Practices. By the Federal Interagency Stream Restoration Working Group (FISRWG)(15 Federal agencies of the US gov't). GPO Item No. 0120-A; SuDocs No. A 57.6/2:EN 3/PT.653. ISBN-0-934213-59-3. GRIFFIN, W.L., 1998, From the mountain to the lake: the Red Hill Creek valley, The conserver society of Hamilton and district, pp.256, ISBN # 0-9683259-0-4. HOLLIS, G.E., 1975, The effect of urbanization on floods of different recurrence interval, Water Resources research, Vol. 11(3), pp. 431 - 435. KARROW, P.F., 1987, Quaternary Geology of the Hamilton-Cambridge Area Southern Ontario, Ontario Ministry of Northern Development and Mines, Mines and Minerals Division, Ontario Geological Survey, Report 255, pp.94. LEOPOLD, L.B., M.G. WOLMAN, and J.P. MILLER, 1964, Fluvial processes in geomorphology, W.H. Freeman and Company, San Francisco, California, pp. 522. MAGALHAES, L., and T.S. CHAU, 1983, Initiation of motion conditions for shale sediments, Canadian Journal of Civil Engineering, Vol. 10, pp. 549 - 544. MOSS, A.J., 1963, The physical nature of common sandy and pebbly deposits. Part II., American Journal of Science, Vol. 261, April, pp. 297 - 343. MOSS, A.J., 1962, The physical nature of common sandy and pebbly deposits. Part I., American Journal of Science, Vol. 260, May, pp 337 - 373. NEWBURY, R.W. and M.N. GABOURY, 1993, Stream analysis and fish habitat design - A field manual, Newbury Hydraulics Ltd., ISBN 0-969-6891-0-1, pp.256 ONTARIO MINISTRY OF NATURAL RESOURCES, 1:10000 Time series air photos ONTARIO MINISTRY OF NATURAL RESOURCES, 1999, Adaptive Management of Strem Corridors in Ontario - Working Draft,Natural Channel Systems - An Approach to Management and Design, Queen’s Printer for Ontario, Ontario, Canada, pp.103, ISBN # 0-7778-2669-0 ONTARIO MINISTRY OF NATURAL RESOURCES, 1994, Natural Channel Systems - An Approach to Management and Design, Queen’s Printer for Ontario, Ontario, Canada, pp.103, ISBN # 0-7778-2669-0 PEACE, W.G. - Editor, 1998, From mountain to lake: The Red Hill Creek valley, W.L. Griffin Printing Ltd, Hamilton, Ontario,pp. 256 ROSGEN, D.L., 1996, Applied river morphology, Wildland Hydrology Press, Pagosa Springs, Colorado,
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ROSGEN, D.L., 1994, A classification of natural rivers, Catena, Vol. 22, pp. 169 - 199. SHIELDS, A., 1936, Application of similarity principles and turbulence research to bedload movement, Mitt Preuss, Verchsanst, Berlin. Wasserbau Schittbau, in Ott. W.P., and Uchelen, J.C., (translators): Pasadena, California Institute of Technology, W.M. Kech Laboratory of Hydraulics and Water Resources, Report No. 167. STEAD, V., 1996, Channel erosion in the upper Red Hill Creek Valley, B.A. Thesis, Department of Geography, McMaster University, Hamilton, Ontario, Canada VISHER, G.S., 1969, Grain size distributions and depositional processes, Journal of Sedimentary Petrology, Vol. 39(3), pp. 1074 - 1106.
Preliminary Natural Channel Design • June 19, 2002 • Water R e g i m e Investigations and Simulations Ltd.