Session: The AEAM Process at Hocker Flat
Friday, February 9, 2007 - 8:00 to 9:15 AM
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| In this session: | |
| Results of WY2006 Geomorphic Monitoring at Hocker Flat | Geoffrey Hales & Scott McBain |
| WY2006 Riparian Monitoring and Experimentation Results at Hocker Flat | John Bair & Sunny Loya |
| Bioaccumulation of Mercury in the Hocker Flat Restoration Area | Roger Hothem, Jason May, Darrin Bergen, Bonnie Trejo & Marissa Bauer |
| Discussion Session: The AEAM Process at Hocker Flat |
Results of WY2006 Geomorphic Monitoring at Hocker Flat
Geoffrey M. Hales, McBain and Trush Inc. PO Box 663 Arcata CA 95518, geoff@mcbaintrush.com,
(707) 826-7794 ext 18
Scott McBain, McBain and Trush Inc. PO Box 663 Arcata CA 95518, scott@mcbaintrush.com
(707) 826-7794 ext 11
The Hocker Flat Bank Rehabilitation Site (RM 78 - 79) was constructed in September - October 2005 and site revegetation was completed in March 2006. As a part of the Trinity River Restoration Program's adaptive management monitoring, site geomorphic changes resulting from the spring 2006 Record of Decision (ROD) Extremely Wet water year release were documented (the peak release was approximately 10,000 cfs and lasted for three days). In addition, site geomorphic changes resulting from the December 2005 peak winter flood (estimated as approximately 26,700 cfs at Hocker Flat) were also documented. This report summarizes results of geomorphic monitoring used to document changes from two peak flow events in achieving Trinity River Flow Evaluation Study (TRFES) and ROD fluvial geomorphic objectives for an Extremely Wet water year.
Geomorphic monitoring consisted of re-occupying and surveying historic (pre-construction) cross sections and evaluating channelbed mobility and scour during the winter peak and spring ROD release. Monitoring results showed: (1) topographic changes resulting from the winter flood and spring ROD release occurred along all cross sections, with the greatest change occurring at the upstream end of the site (topographic changes may have been exacerbated by erosion-prone constructed surfaces), and; (2) bed mobility and bed scour thresholds were exceeded from both the winter flood and, more importantly, the spring ROD release, although only partial mobilization of the spring release marked rock sets occurred.
In the context of the fluvial geomorphic objectives outlined in the TRFES and ROD, bed mobility objectives were met by the December 2005 peak winter flood but were not met by the spring ROD release (D 84 particle mobility for each marked rock set ranged from 92% to 100% for the winter flood but only ranged from 9% to 36% for the spring release). Bed scour objectives were generally not met; only one cross section recorded scour from the December flood that was deep enough to meet TRFES objectives (both scour cores on the cross section were completely scoured and results suggest scour exceeded 2 D 84's depth), and no scour cores recorded scour from the spring release that was deep enough to meet TRFES objectives. However, high river stage during spring 2006 prevented geomorphic experiments from being replaced in their previous winter monitoring locations (they were relocated higher up on the bar surface). Because of this condition, the spring mobility and scour results presented are likely lower than would have been recorded if the winter locations were reoccupied, but the degree of mobilization and scour would still likely be less than what was recorded by the December 2005 flood.
Presentation notes:
The high flows that occurred in December 2005 were not expected. Canyon Creek may have contributed an extra 10,000 cfs to these December flows. High flows resulted in the constructed channel both eroding and filling with up to 6' of bedload in upper cross sections at Hocker Flat. ROD release resulted in bed lowering from earlier flow and resulting in silt depositing in furrows on the bed. ROD flows showed less mobility than the December flow, but part of this may have been due to marked rocks being placed at higher sites for the ROD flows. ROD flows should have moved 35-100 % of the rocks. December 2005 flows mobilized the D84 size fraction. Overall the results were good.
Questions: Is this the most active site. Yes. Shouldn't there have been more change? And are there any suggestions for construction modifications? There were big changes at top and these could migrate downstream over time. Not sure what you could do differently to accentuate change.
WY2006 Riparian Monitoring and Experimentation Results at Hocker Flat
John H. Bair, McBain and Trush Inc. PO Box 663 Arcata CA 95518, john@mcbaintrush.com
(707) 826-7794 ext 14
Sunny S. Loya, McBain and Trush Inc. PO Box 663 Arcata CA 95518, sunny@mcbaintrush.com
(707) 826-7794 ext 21
The TRFES and ROD riparian objectives for an Extremely Wet water year (and therefore the objectives of the WY2006 managed release) are twofold: 1) to periodically scour woody riparian vegetation on lower alternate bar surfaces, and 2) to regenerate woody riparian vegetation on upper bar alternate bar surfaces and floodplains. The riparian mortality objective inhibits young woody riparian vegetation (<3 yrs old) from getting establishing along the low flow channel margins and prevent riparian encroachment leading to channel simplification. The riparian regeneration objective encourages the natural establishment and growth of riparian vegetation on floodplains and increase species and age diversity overall (HVT and USFWS 1999).
Because WY2006 was an Extremely Wet water year, both objectives could be tested at the newly constructed Hocker Flat bank rehabilitation site. Riparian scour was monitored for two high flow events: a December 2005 tributary-generated event (peak flows approximately 26,700 cfs at Hocker Flat) and the May 24 to 26 ROD flow release (three day release of approximately 10,000 cfs). Riparian initiation was monitored on the recession limb following the May 24 to 26 ROD release. The 2006 ROD release started with a sustained peak release of approximately 10,000 cfs, followed by a seven day bench of 8,500 cfs, then followed by an eight-day bench of 4,800 cfs intended to initiate riparian seedlings on constructed floodplains. This 4,800 cfs bench created moist seedbeds on surfaces of constructed floodplains at the Hocker Flat site providing nursery sites for riparian hardwood initiation. Flows were ramped down to 2,000 cfs at a rate predicted to allow germinated seedling roots to follow a declining water table.
Hocker Flat was constructed in the fall 2005 and therefore had no riparian woody plant seedlings to scour during the winter and spring flood peaks. Monitoring of scour induced mortality focused on the willow root sprouts removing after construction. Riparian mortality monitoring after the December 2005 tributary peak and May 2006 ROD peak release revealed that scour depths were insufficient to significantly remove root sprouts. Given two large flood magnitudes in WY2006, the likelihood that the root sprouts will be scoured is low. The riparian berm is likely to re-form along the low water edge at future construction projects without further removal effort during construction.
Riparian monitoring, to evaluate how managed spring releases affected riparian woody plant initiation on constructed floodplains at Hocker Flat, focused on black cottonwood as an indicator species. Black cottonwoods are one of the earliest seed dispersers. Physical conditions that facilitate black cottonwood initiation would also meet the requirements of woody plants that disperse seeds later. Seed dispersal period, dispersal rate, seed germination rate, root growth rate, initiation success, and inundation tolerance were assessed for black cottonwood. Other physical factors were assessed, including rate of stage decline, soil moisture dynamics, and hourly air temperature fluctuations.
Black cottonwood seed dispersal period occurred before peak releases and the 4,800 cfs bench. Woody plants dispersed seeds following previously quantified patterns (McBain & Trush 2006). Seed germination and formation of a tap root occurred for most remaining black cottonwood seeds within 36 hours of landing on sterile sand. Root growth rates were much slower than reported in the literature (i.e., 0.008 ft/day rather than 0.08 ft/day), but were sufficient to keep up with the abundant soil moisture 0.5 feet below the ground surface. The recession rate of releases from 4,800 cfs to 2,000 cfs appeared to meet the physical requirements for riparian initiation and seedling development. Despite adequate soil moisture 0.5 feet below the ground surface most of the young seedlings died. Hourly air temperature data collected near Hocker Flat was evaluated and compared to previous years when high densities of successfully initiating seedlings were observed, indicating that the single greatest factor affecting the survival of recently germinated seedlings in 2006 was the lethal effect of high day-time air temperatures (i.e., 19 of 45 days between late June and July were over 100ºF), compounded by the additional heating of unshaded cobble/gravel constructed floodplains.
Earlier peaks would better ensure that the riparian initiation bench and subsequent receding limb intersected the greatest number of woody riparian plant seed dispersal periods. The availability of multiple species seeds over the receding limb would ensure germination success over a wide range in floodplain topography and increases in riparian vegetation diversity. Soil moisture decay followed river stage changes until the soil moisture front was approximately 0.5 ft below the floodplain surface, after which the decay slowed. Root growth rates are sufficient to follow the declining soil moisture front down to a depth of 0.5 feet. When root reached stable soil moisture conditions at a depth of 0.5 ft, seedling survival was less dependent on declining river stage and more dependent on maximum daily air time temperatures. From a flow management perspective, once river stage drops 0.5 feet below floodplain surfaces, river stage recession could be increased because there is still sufficient soil moisture at a depth where recently germinated seedlings roots have grown; the conserved water volume could be re-allocation to other restoration objectives.
McBain & Trush 2006. Riparian Monitoring at Four Proposed Bank Rehabilitation Sites and One Bank Rehabilitation Site. Final Report. Prepared for Trinity River Restoration Program, Arcata , CA .
USFWS and Hoopa Valley Tribe 1999. Trinity River Flow Evaluation. Final Report. US Department of the Interior, Washington D.C.
Presentation notes:
Seed dispersal appears to be good at this site. It is possible that the prolonged bench could be shortened to 3 days and could be reduced at a higher rate. This would allow for more water to be allocated elsewhere.
Questions: Were flow objectives met? Many species are likely seeding in but survival is uncertain yet. How can you enhance survival? Herbivory was not noticed. Mortality is mainly due to high temperatures and this can't easily be controlled.
Bioaccumulation of Mercury in the Hocker Flat Restoration Area
Roger L. Hothem, USGS, roger_hothem@usgs.gov, (707) 678-0682 Ext. 626
Jason T. May, USGS, jasonmay@usgs.gov, (916) 278-3079
Darrin R. Bergen, USGS, dbergen@usgs.gov, (707) 678-0682 Ext. 625
Bonnie S. Trejo, USGS, btrejo@usgs.gov, (707) 678-0682 Ext. 620
Marissa L. Bauer, USGS, mbauer@usgs.gov, (916) 278-3299
Aquatic invertebrates play a critical role in aquatic ecosystems by influencing fundamental processes such as decomposition, primary production, and nutrient and contaminant spiraling, and they form vital links between primary producers and secondary consumers, such as amphibians and fish. This study was conducted to evaluate the potential effects of restoration work in the Hocker Flat area on mercury bioaccumulation by aquatic macroinvertebrates. A baseline study was conducted in 2003 and 2004 in which aquatic insects were collected prior to restoration to characterize mercury concentrations in biota at sampling sites that were also sampled for sediments. Following restoration activities, aquatic invertebrates were collected in fall of 2006 at the same locations to evaluate potential changes in mercury bioavailability. However, since analyses of these samples have not been completed, we cannot evaluate the effects of the restoration on mercury bioaccumulation
Two trophic levels of macroinvertebrates were collected for this study. Predatory insects (e.g., stoneflies, water striders, dragonflies, dobsonflies, and predaceous diving beetles) have been previously collected by the USGS in other areas in the Trinity Watershed and other watersheds with histories of gold or mercury mining. These taxa have been shown to be consistent indicators of localized mercury contamination and have been used to compare mercury contamination within and among watersheds. We also collected larval web-spinning caddisflies and various mayflies, common prey items of salmonids. Such invertebrates may serve as indicators of mercury loading to secondary consumers such as juvenile salmonids and other resident fish species.
Collections were made at one site on the Trinity River above the restoration ( Dutch Creek Bridge ), one site downstream of the restoration, one site on Canyon Creek just upstream of the Trinity River, three Trinity River sites within the restoration area, and two wetland areas within the restoration area. Data from samples collected prior to restoration efforts were compared to samples from the East Fork Trinity River, and Brandy Creek , a reference site in the Whiskeytown National Recreation Area. Total mercury and methylmercury values prior to restoration efforts were generally low (below 0.1 µg/g, wet weight in most samples), with few statistical differences between sample sites at Hocker Flat. No sites showed consistently higher or lower patterns of mercury concentrations, although some levels were slightly higher in invertebrates from the wetlands sites. Mercury concentrations from Hocker Flat were generally comparable to results from the uncontaminated reference site at Brandy Creek . Mercury concentrations in samples from the East Fork Trinity River, especially near the Altoona mercury mine, were generally much higher than Hocker Flat.
Presentation notes:
There is no known biological functions for mercury (Hg) and it is toxic. There are natural sources of Hg but the gold extraction process is a larger source. Fish eating advisories exist for Trinity Lake and for the East Fork Trinity River. The East Fork is contaminated by Altoona Mine and has highest concentrations in stoneflies and trout concentrations are close to EPA advisory levels. In general, the predatory insects tended to have higher Hg concentrations than the grazing insects. There were no differences between 2003 and 2004 collections. 2006 have not yet been analyzed. Spring concentrations were higher than fall concentrations.
Questions were combined with the following discussion session.
Discussion Session: The AEAM Process at Hocker Flat
Panelists: Geoffrey Hales, John Bair, and Roger Hothem
What are the best fish to measure at Hocker Flat for Hg? Brown trout may be better since they live there year long. What is the overall impact of restoration on Hg. There is concerned about the sluice sands that become exposed as they have high Hg. Methylation of Hg causes biota to take it up. Rainbow were the most abundant fish sampled. Levels of 0.2 µg/g is below the EPA level even in the EF Trinity River .
How was cottonwood seedling survival estimated? They first observed low germination success of planted seeds and then saw low survival too. But this is expected. Why so few germinations? May be due to inexperience with germinating the seeds. Bair did not look at purposeful revegetation efforts.
There appear to be great changes in the bed at Hocker Flat following the high flows. Is there any advice for future restoration regarding geomorphic effects? Changes in upper end were not solely due to the restoration efforts. For example, Canyon Creek helped to create changes. Better design is possible, but it depends on hydraulics and planform. If a meander were present, changes may be greater-e.g., it may be site specific. What "great change is," is actually difficult to quantify and depends on perspective. Were changes due to erosion or channel migration? Changes were due to new construction, and was susceptible to erosion. Downstream bars are forming and if these continue as depositional area, this will encourage channel migration. It is tricky to extrapolate too far after only 12 months.
Methods used to measure channel changes due to high flows-are alternative methods such as aerial surveys useful? or are there any ideas about the values of different methods? Both methods are useful. Aerial photos show changes at a large scale; cross sections help to explain why things happen. The amount of sampling needed is not known. Cross sections alone are not as useful as compared to when there are combined with photos. A level-survey gives much greater precision, e.g., 0.001 foot versus 1 foot resolution in LIDAR.
Downstream of Hocker Flat, did anything happen to the remaining berms? These berms were still left after the high flows. There, sand was deposited and the berm grew. But there was only one cross section so not sure if this is representative of all berms.
One thing we learned at Hocker Flat is, to increase geomorphic change, we may want to leave some patches of existing vegetation and we may want to incorporate more micro-topography and with less uniformity.
How much geomorphic change might be expected upstream at Lewiston where there is less tributary accretion? Certainly there should be less, maybe we can incorporate more complexity to encourage change.
Presentations where researchers give views as to whether flow evaluation objectives were either met or not met is very useful.