Session: Integrating Habitat and Geomorphic Process
Friday, February 9, 2007 - 9:15 to 10:45 AM
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| In this session: | |
| Preliminary Results of 2006 Geomorphic Mapping | Dave Gaeuman |
| Assessing the Risk of Redd Scour on the Trinity River | Christine May, Bonnie Pryor, Tom Lisle & Margaret Lang |
| Initial fish response to July 2006 Hatchery Gravel Augmentation Project | Gregory Pasternack |
| Integrating salvage LWD in rehabilitation site construction | John Klochak |
| Discussion session: Assessing the risk of redd scour on the Trinity River | |
Preliminary Results of 2006 Geomorphic Mapping
Dave Gaeuman, Trinity River Restoration Program, dgaeuman@mp.usbr.gov, (530) 623-1813
Among the primary objectives of the Trinity River Restoration Program is to create and maintain spatially complex channel morphology in the Trinity River . This objective is motivated by the well-established principle that complex channel morphology provides the physical basis for diverse, high-quality aquatic and riparian habitat. It has been proposed that channel complexity in the Trinity River be assessed through the development of an integrated geomorphic/habitat mapping strategy. It is proposed that stream morphology and habitat can be viewed in terms of geomorphic assemblages defined by particular arrangements of topographic elements, particular substrate and hydraulic characteristics. These physical attributes translate into particular habitat values. This approach recognizes that physical habitat emerges from the synthesis of geomorphic structure, substrate, bank characteristics, riparian vegetation, and woody debris. Approximately 20 river miles were mapped in the late summer of 2006 as an initial effort to develop and implement this strategy. Mapping was conducted in the field on a 2006 air photo base, and focused on gross topography of the bed, bed surface grain sizes, and bank conditions. Some useful qualitative conclusions emerged from this effort, including the verification of tributary delta scour, bar aggradation, bank erosion, the entrainment of small boulders during the 2006 release, and the recognition that substantial lengths of river are confined by bedrock or boulder banks. Although a relatively small portion of these maps have been digitized to date, some semi-quantitative analyses pertaining to grain size distributions, fine sediment storage, and bank conditions have been conducted. Refinement of mapping methods, development of reach-scale geomorphic unit classes, addition of a riparian component, and greater integration with aquatic habitat values is planned.
Presentation notes:
Attempting to map geomorphically 40 miles of river; only finished 20 miles so far. Mapping grain size (D50 and D90), bank characteristics (eroding and nonalluvial), and habitat types. This can provide guidance for future restoration. We need an integrated mapping approach as a primary TRRP assessment strategy. We want in-channel complexity, transverse bars, riparian floodplains with a variety of shrubs and topography. But, no one knows how to do this.
Question/comment: We need to map, and then link, geomorphology to habitat.
Assessing the Risk of Redd Scour on the Trinity River
Christine L. May, James Madison University , maycl@jmu.edu
Bonnie S. Pryor, Jeff Anderson and Associates, bonnie@northernhydrology.com
Tom E. Lisle, U.S. Forest Service, Pacific Southwest Research Station, tel7001@humboldt.edu
Margaret M. Lang, Humboldt State University , mml1@humboldt.edu
A critical knowledge gap for implementing peak flow releases during the winter rainy season is predicting the potential scouring of spawning redds downstream of Lewiston dam. To address this issue an understanding of the relationships among river discharge, bed mobility, and scour depths in areas of the streambed heavily utilized by spawning salmon is needed. Our approach coupled numerical flow modeling and empirical data to quantify spatially explicit zones of differential bed mobility and identify specific areas where scour is deep enough to impact redd viability. Boundary shear stress values were predicted from the USGS's Multi-Dimensional Surface Water Modeling System for a segment of the Trinity River near Junction City (Sheridan Bar). From model-generated shear stress and fine-scale mapping of local particle size distributions, Shield s values were calculated to identify areas of differential bed mobility.
Four high flow events occurred during the study, which provided an opportunity to model hydraulic conditions over a range of peak discharges (6,350 - 16,700 cfs) and to measure scour. Spatial patterns of bed mobility based on model predicted Shields stress indicate that a zone of full mobility is limited to a central core along the thalweg, which expands with increasing flow strength. Deep scour was not widespread and rarely reached depths great enough to result in disturbance to eggs at the range of flows experienced during the study. The likelihood and maximum depth of measured scour increased with increasing modeled Shields stress.
Site selection preferences of spawning Chinook also influenced their risk of scour. Statistical analysis indicates that redds are preferentially located in shallow, high velocity areas with relatively coarse substrate and in close proximity to streambanks. These site selection preferences correspond to areas of the streambed that are least likely to become mobilized or risk deep scour. Because redds are being constructed in areas of inherently lower mobility, they have a lower risk of scour than the surrounding bed area. This suggests that extremely large flow events will be necessary to mobilize areas that are preferentially used for spawning. The trade-off for spawning in relatively stable portions of the bed is that flushing of fine sediment from the subsurface occurs very infrequently and gravel permeability may become limiting.
In areas identified as potential spawning habitat, the envelope of potential scour and the probability distributions of scour depths for ranges of Shields stress can be used to assess the risk of redd scour. For Shields stress <0.04 there is a very low risk of redd scour because the bed is not fully mobile and the maximum scour potential did not exceed the average depth to top of egg pocket (23cm). For Shields values between 0.04 and 0.06 the bed transitions from partial mobility to full mobility and there is a low risk of redd scour. Within this range of Shields values the envelope of potential scour encompasses the entire depth of the egg pocket (23 to 30cm); however, maximum scour potential represents the tail of a skewed distribution and the probability of scour >23cm is only 4%. For Shields stress >0.06 the streambed is fully mobile and there is a moderate risk of redd scour. The scour potential line exceeds egg pocket depths; however, the probability of scour >23cm is still very low (7%). Based on a strong relationship between reach averaged Shields values and scour depths from a compellation of studies on the Trinity River , we propose that this strategy for assessing risk is transferable to other areas of the river.
Presentation notes:
Looked at the Sheridan Creek area. Used a two-dimension, steady-state hydrology model. Shields stress is a factor that describes mobility of the bed-0.03 is partially mobile; 0.06 is fully mobile. Most predicted scour is less than the depth to buried redds (23 cm). Even at Shields stresses of 0.06, the probability of redd scour is only 7 %.
Questions: Is there a plan to use this approach in gaming? No, but there should be.
Initial fish response to July 2006 Hatchery Gravel Augmentation Project
Gregory B. Pasternack, Department of Land, Air, and Water Resources, University of California at Davis, gpast@ucdavis.edu, 530-754-9243
The Lewiston Hatchery reach (LHR) of the Trinity River was determined by fisheries biologists to lack adequate physical habitat to support the spawning and embryo incubation life stages of anadromous salmonids present in that reach. As a management action to address this concern, UC Davis and the Trinity River Restoration program performed baseline research and river-rehabilitation design activities that ultimately led to the selection of a final design for a project to re-introduce natural hydrogeomorphic process promoting habitat heterogeneity and supporting spawning. The details of the baseline research and design alternatives are available at shira.lawr.ucdavis.edu/trinity.htm. The final design called for 1) elimination of the pre-existing rock-weir structures to redistribute slope more naturally, 2) widening of the channel at riffle crests and narrowing at pools to focus high-flow scour in pools and diminish it on riffle crests, 3) addition of 9000 tons of coarse sediment to be contoured according to the design grading plan, and 4) addition of boulders to create local hydraulic diversity. Institutional delays in implementation of the project resulted in cost increases associated with transportation of the gravel to the project site. Consequently, the project is being constructed in two stages. The first stage involving site excavation, placement of 2500 tons of course sediment, and placement of boulders was performed during summer 2006. Placement of the remaining 6500 tons of coarse sediment and associated boulders is planned for summer 2007. Observations of fish usage of the first-stage project area are on-going, and preliminary results will be reported.
Presentation notes:
They used the SHIRA approach of the previous study: 2-D model and assess scour depths. This is called an indicator approach by ecologist: to restore for one species but restoration should benefit other species. The design of the Lewiston project was constrained by the presence of the hatchery facility. The actual choice was based on a series of meetings. They have been told that fish have been observed using the gravel for spawning. Fishermen responded to their project with varying support. The local fishermen were less supportive, and they did not like the 2500 cfs flows; the non-local fishermen seemed to like the project more as it provide better access.
Questions: Use by spawners is a useful measure of success, but is fitness increased? Success of the fry is paramount. Pasternack noted that the choice of the design was not necessarily his but of the TRRP as a group. Studies show that flow regulation does not work by itself, but active restoration is important together with flows. 2-D modeling and scour analysis is helpful.
Integrating salvage LWD in rehabilitation site construction
John Klochak, Trinity River Restoration Program, jklochak@mp.usbr.gov, (530) 623-1810
The Trinity River Restoration Program built the Canyon Creek Suite of riverine rehabilitation projects at Conner Creek, Valdor Gulch, Elkhorn, and Pear Tree Gulch, located between river mile 73 and 78 on the Trinity River in the Fall of 2006.
As originally designed, riparian trees at the restoration sites were to be removed, and disposed of off-site, adding to project costs and removing potential valuable habitat components from the river. It is widely acknowledged in this ecoregion that LWD interacts with water and sediment to create channel complexity and is an important component of aquatic habitat. Thus, provisions were made to incorporate salvaged large woody debris (LWD) into the project designs during construction.
A total of 117 pieces of LWD were placed at the four sites. Based on literature review, site conditions, available heavy equipment, and personal experience, several different placement designs and techniques were used.
This presentation will describe placement techniques and show some example LWD placements, examine the increase in LWD loading in the treatment reach, and discuss future efforts to monitor the LWD placements and assess effectiveness.
Presentation notes:
A major question is whether we dispose of vegetation that is being removed or can it be used? Clearing of trees is expensive. At the Valdor Gulch site 119 trees were re-used as a large woody debris (LWD) project; two were removed by wood cutters. These trees resulted in a 40 % increase in LWD within the bankfull zone. Over the coming years, retention, recruitment, and scour and fill around the new habitats will be monitored.
Questions: Was there any backlash regarding added wood as a navigation hazard? Not yet. Wood is natural and the amounts normally recruited by high flows is much more than we added here. Black alders are not long lived, will they become an important source of LWD? Yes, lots of recruitment is expected.
Discussion session: Assessing the risk of redd scour on the Trinity River
Panelists: Dave Gaeuman, Christine May, Greg Pasternack, and John Klochak
We seem to need about ten-fold more habitat than we originally had, how would we do accomplish this? Tributary junctions in undammed rivers have lots of potential for complexity and would be one place to focus. We want to foster diversity and complexity into actions. We don't want uniform parking-lot type floodplains. Diversity may foster more diversity. Use of the trees is important. Methods are in place to do this, but it also depends on political will and money. We need these resources if you want to restore 40 miles.
How much is cost a factor in design and is the expensive, 2-D hydrodynamic simulation going to be used in future designs? The money is more of a consideration for the number of sites that can be built and less on what is done at a particular site. Downstream sites are more expensive due to the need to treat the raised terraces. As we modify designs to incorporate more topographic complexity, these can be less expensive as they may require less ground moving. Modeling will not likely be done at most other sites. Lewiston was a high profile site due to fish use and fishing pressure. The design attempted to incorporate natural processes. But the Lewiston reach really can't widen or narrow due to the hatchery constraints.
How likely is the 11,000 cfs flow to be able to really change the river? Is there enough energy? This is difficult to answer as we don't know how much habitat we need or how much we want to get. We should expect our channel to be sized to the flow regime and we can calculate the resultant size-we shouldn't expect a large fluvial river. The system may be becoming less dynamic and therefore you may want to consider adding coarse sediment. It is not just water and sediment, biota plays a role too. 11,000 cfs is likely not enough to stop re-encroachment by willows. Bedrock control will prevent restructuring by flows; meander pattern will not change as bedrock controls this and bedrock will not change by 11,000 cfs flows.
Are there other areas that could benefit by similar projects as Lewiston ? Yes, the Cableway and the straight, "boring sections" as noted by Dave Gaeuman.
North Coast Watershed Assessment Project (NCWAP) used aerial photos together with mapping and this was powerful. This success may have implications for the TRRP.
What is the proper balance between mitigation by hatchery and restoration? (No real answer was offered.)
What about new designs? Costs of design alternatives are considered; and this does drive the level of design considered. Microtopography is a good thing and LWD are great things to incorporate into the design. Trinity River is string of pearls: it alternates from wide to constrained sections. Vegetation does seem to be in equilibrium with post-dam flows.
Can ROD flows redistribute vegetation? What is the persistence of the actions? Any sense? And how to measure success? We can measure physical habitat but it remains to be seen whether this recovers the fishery. Measure of success is how well the fish are doing. We need to understand what limits the natural production (what is the limiting factor?). Otherwise we're shooting in the dark. We do need to move beyond "Did this rock move?" Biologist do not agree about this river; some think it is spawning limited, and they have been shut out. How does mortality vary at different life stages?
Will we be stuck because slope is not steep enough? Slope does seem to be steep enough; it is at least 0.4 % in the upper river and this should be enough to get habitat. Downstream it is lower -- 0.2 to 0.3 %.
What is potential for scouring areas below dam? Pasternack's website has predictions of scour. Danger of having so much spawning near dam is that scour could be too great. Down river redds are at lower risk of scour.
Questioned the notion that the Trinity River is actually "spawning limited." Most biologists seem to agree it is fry-habitat limited based on the flow evaluation and on SALMOD modeling.