River-Lab

Actively incising Lower Tassajara Creek in Dublin, California, was restored as a compound channel in 1999-2000 to mitigate incision and provide flood conveyance capacity to reduce flood risk to an adjacent greenfield residential development. The project benefitted from a wide floodplain corridor set aside during development, allowing a rough vegetated overbank channel with a design capacity to carry the 100-year flood. Several years of cross-sectional channel surveys conducted under an informal monitoring program from 2000 to 2006 indicated that active incision was largely attenuated following the restoration, with some minor incision still evident and low-flow channel complexity just beginning to develop. This research evaluates Lower Tassajara Creek 20 years after its restoration, investigating ongoing channel evolution, incision and aggradation, and floodplain reconnection, and discussing channel conditions in the context of the catchment land use history. I repeated and overlayed a series of cross-section surveys to detect channel incision and overbank deposition, documented field observations of channel condition, and cross-referenced against LiDAR terrain data to detect depositional landforms on the floodplain. I also developed a one-dimensional hydraulic model to better understand current flood conveyance capacity, using channel roughness back-calculated using measured high water marks from a recent storm. Preliminary results suggest overbank deposition has occurred in some locations, particularly in the upper reaches, while shallow slopes and fine sediment in the low flow channel throughout the project indicate a depositional environment. While active incision appears to have halted, entrenched conditions persist in the reach with a deeper low-flow channel sized to carry the 5-year flow. There may be opportunities to improve floodplain connection by adding woody debris to push more frequent flows out of the low flow channel, but additional hydraulic model validation and testing will be required to determine where flood conveyance capacity is sufficient to support such an intervention.

The headwaters of Blind Horse Creek originate in the highest point of the Trinity Alps. It is a tributary to the South Fork Salmon River located in the Klamath National Forest. In the summer of 2021, wildfires burned 114,433 acres in the Salmon River watershed. For this subbasin of the greater Klamath River Basin (KRB), this was the greatest number of acres burned in a single year on record. The River Complex was a large-scale, high-severity wildfire that burned all around the South Fork Salmon River leaving steep drainages barren of any vegetation. The following year, 2022, summer rains brought 1-2 inches of rainfall to the landscape and triggered a debris flow within the Blind Horse Creek drainage. Although initially a major disturbance to the river system, over time the new sediment moving through the system deposited behind Large Woody Debris, boulders, and eddies, creating new beaches and sand bars distributed throughout the river. The delivery of fine sediments to streams post-fire can initially degrade salmonid-rearing habitat, however, these new sand deposits have the potential to be viable rearing habitats for other native fish species, such as Pacific Lamprey (Entosphenus tridentatus), and their larval stage, ammocoetes. Having a baseline of how the sediment is distributed throughout the system can indicate habitat change and distribution for these evolutionarily primitive and culturally significant fishes. Our work documents the current distribution of sediment and identifies potential lamprey rearing habitat through cross-sectional elevation surveys, facies map documentation, and the measurement of viable sand bars. The description of current site conditions after a large disturbance can help inform restoration strategies for the river and perpetuation of habitat for sensitive species such as salmonids and Pacific lamprey.

Vegetation restoration projects throughout the American Southwest have yielded positive outcomes for degraded desert streams, including the Mojave River restoration at Afton Canyon in the Eastern Mojave Desert (Egan, 1999; 2016; Bunn et al., 2003). Although rare, beaver translocation has demonstrated success as a passive desert river restoration strategy at the Price and San Rafael Rivers in eastern Utah and the San Pedro River in Arizona (Soykan et al., 2009; Doden, 2021; Sandbach, 2023). The success of translocated beaver populations is determined by mortality rate and site fidelity, as dictated by habitat quality (Colleen & Gibson, 2000; McKinstry & Anderson, 2002; Petro et al., 2015; Morris et al., 2021; Bilby & Moseby, 2023). In deserts, beaver habitat is restricted to riparian forests (Rutherford, 1964; Bee et al., 1981; Welch et al., 1993). The restoration project at Afton Canyon has facilitated the return of native willow and cottonwood populations and beaver sightings have increased (Egan, 1999; 2016; MDRCD, 2022). It is likely that a combination of natural beaver recolonization and translocation would facilitate further habitat restoration.

In 1996, the National Park Service (NPS) restored a 100-yard section of Lobos Creek in San Francisco. In this study, we evaluated the presence of invasive species within the Lobos Creek restoration project. The restoration site is not actively managed by any organization or volunteer group. Our research is unique in that it is a comparison between an unmanaged restoration site and an actively managed area along the same creek. Our project takes into account the historical land use changes within the area to provide context on how plant communities have been impacted. We found that the unmanaged Lobos Creek restoration site has reduced the presence of invasive species, in comparison to the managed and unrestored upstream portions of the creek.

In recent years, river restoration has shifted towards natural, process-based approaches rather than fixed, engineered solutions. This new emphasis on natural approaches was implemented in a restoration design and subsequent experiment in the Tilden Park Golf Course reach of Wildcat Creek in Berkeley, California, USA. The restoration design implemented step-pools to address bank erosion and encourage channel stabilization, while the experiment highlighted the creek’s ability to self-organize these desired step-pool formations without the need for human interference. The Restoration and Experimental Reaches were monitored consistently from 2012 to 2017 and again in 2022, and found that after the addition of step-pools, the channel bed remained fairly stable without significant aggradation or erosion. Our study conducted a post-project monitoring of the Restoration and Experimental Reach, to gain further insights on potential changes in the channel and step-pool morphology, as well as identifying three potential contributing factors: vegetation growth, precipitation, and disturbances.

Previous monitoring in 2022 noted that vegetation management greatly influences channel morphology, and willow growth in the Restoration Reach could thereby negatively impact channel stability. Further, since the most recent monitoring in 2022, a series of large winter precipitation events may have altered the channel morphology but have not yet been accounted for in analysis. Additionally, a willow fell into the Experimental Reach during the winter of 2015-2016, accumulating debris and causing aggradation. While the effects of this disturbance are noted through cross-sections taken in 2016 and 2017, it is unclear how the disturbance impacted step-pool morphology as well as longer-term trends in channel morphology. Through three days of field work, we surveyed cross sections, performed pebble counts, and observed the step-pool formations and coinciding slope in the restoration and Experimental Reach. Informally, we also replicated photos taken yearly at various perspectives along the creek and recorded occurrences of riparian species. We situated our data in the context provided by documents from and interviews with Dr. Anne Chin and Dr. Patina K Mendez, as well as Restoration Design Group (RDG). Results show that channel morphology, sediment composition, and step-pool morphology are heavily influenced by vegetative growth, precipitation, and the log jam disturbance. Specifically, the channel cross sections aggraded due to willow growth and the log jam, though the Experimental Reach impacted by the log jam has recently shown signs of incising and returning to pre-log jam conditions. High flows greatly impacted sediment composition, as high flows allowed for increased transport capacity, flushing out the coarser material added by RDG in the 2012 restoration. Without replenishment of coarse material, the sediment supply returned to pre-construction fines, decreasing grain size. High flows and the log jam also influenced step-pool morphology, high flows allowed for an increase in the number of step-pools, and the log jam allowed for a decrease in average slope and average five largest rock sizes.

This paper presents historical overviews and original ecological surveys on the North Fork of Strawberry Creek in Berkeley, California to better inform the Kingman Hall Creek Restoration Project. Analysis of geomorphologic changes in the North Fork of Strawberry Creek during urbanization reveals the legacy of alterations on contemporary ecology. Case studies varying in time, scale, and approach contextualize restoration efforts in the entire Strawberry Creek Watershed. The impacts of urbanization and culverting are evidenced by an ecological snapshot of current creek conditions between LBNL and the UC Berkeley Campus. Rod and level topographic surveys, ArcGIS permeability analysis, vegetation analysis, avian surveys, and macroinvertebrate counts conducted at three distinct locations along the North Fork provide a multipronged baseline survey of current conditions. Topographic surveys show a higher degree of incision below culverted stream sections. ArcGIS permeability analysis reveals a highly urbanized watershed, especially around the restoration project site. Vegetation analysis shows the prevalence of invasive species in urbanized riparian ecosystems. Avian surveys found the majority of birds in riparian areas of the North Fork to be generalist ground foragers. Finally, macroinvertebrate surveys found that the complexity and richness of benthic insects decrease after culverting, suggesting a need for further restoration work along the creek. Our surveys found that the impacts on stream health due to culverting and urbanization are beyond the scale of the Kingman Hall Creek Restoration Project. This paper is intended to provide a baseline for future research on the North Fork.

Sea-level rise will have extreme impacts on coastal estuaries, including freshwater sources like rivers and creeks. Though freshwater linkages are critical to overall estuarine health, few studies have explicitly considered how sea-level rise and saltwater intrusion will impact riparian vegetation composition or community health in freshwater creeks adjacent to tidally influenced systems. Our study sought to identify the historical and current conditions as well as projected vulnerabilities for the lower section of Carneros Creek, the main freshwater source for the Elkhorn Slough, in Monterey County, California. To describe historical and current conditions of Lower Carneros Creek, we assessed historical maps, surveyed riparian vegetation using the rapid assessment method, and evaluated drinking water well data for evidence of existing saltwater intrusion. To assess future sea-level rise impacts for Lower Carneros Creek, we mapped previously modeled groundwater rise and saltwater intrusion footprints under a 0.25m sea-level rise scenario. We found that the Western lower section of Lower Carneros Creek is currently characterized by the presence of halophytic, tidal wetland species while the Eastern upper section is dominated by freshwater, riparian species. Our results also showed that even with tidal controls, sea-level rise induced groundwater rise and saltwater intrusion will impact Lower Carneros Creek’s hydrology and likely alter riparian vegetation composition. In response to these findings, we presented management considerations for Lower Carneros Creek that account for historical conditions, broader estuary-wide conservation goals, and public health concerns for communities living in the floodplain.

Our post-project monitoring research focuses on a natural beaver dam on French Creek in the Scott River Watershed in Siskiyou County, CA. The dam exists on a stretch of the creek with several beaver dam analogues (BDAs), which have been implemented by the Scott River Watershed Council in the hopes of combatting incision in the system and recruiting beaver to maintain the structures. French Creek in particular is an important spawning ground for the threatened coho salmon, so the impacts of the dam on fine sediment are of particular interest. Since the installment of the BDAs on French Creek, a beaver family has colonized the site and built a natural beaver dam. In 2021, high flows led to a breach in this dam. Scott River Watershed Council (Council) developed plans to fortify it using similar techniques used in the nearby BDAs. These plans will be implemented in November 2023, one week after this survey.

This dam breach presented the unique opportunity to analyze the surrounding area before its reconstruction, providing both post-breach and pre-reconstruction information on beaver presence, groundwater levels, channel morphology, and sediment grain size. We found evidence of continued beaver activity at the site. Groundwater levels were lower compared to pre-breach data from 2020. Sediment grain size was bimodal directly below the breached dam as compared to an upstream site with imported gravels, potentially indicating a release of fine sediment during the breach. Given the impact of fine sediment on salmon spawning, these fluxes of sediment should be carefully studied and managed. Comparable cross-section data did not exist for the studied reach, so we cannot draw conclusions about the impact of the breach on these metrics, though they may be used going forward to assess the influence of the artificial dam repair.

The current interest in "multibenefit projects" that balance ecology, flood control, and social use in urban rivers makes developing sound theory and methods for social assessments of urban rivers a pressing concern. "Social connectivity" is one theoretical approach to assessing the relationship between the social use and physical condition of rivers. In this study we apply a social connectivity analysis to the American River Parkway in Sacramento, California. We combined observations of channel form with in person counts of users and activities, interviews with users, and reviews of planning documents to conduct a post project assessment of some of the major goals and use assumptions that informed the planning of the Parkway. We found that channel form and access to the river largely drove use patterns, many uses were quotidian and conventional but the largest user groups were there for special occasions, and that users viewed the Parkway positively but had low awareness of flood control and modifications to the hydrology. The results may be relevant to planners or researchers studying urban rivers and their use as public spaces.