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Geology topics

Daniel M. Hanes

Publications and source records attributed to Daniel M. Hanes.

15 recordsLinked to original sources
USGS2018

Before the storm: Antecedent conditions as regulators of hydrologic and biogeochemical response to extreme climate events

While the influence of antecedent conditions on watershed function is widely recognized under typical hydrologic regimes, gaps remain in the context of extreme climate events (ECEs). ECEs are those events that far exceed seasonal norms of intensity, duration, or impact upon the physical environment or ecosystem. In this synthesis, we discuss the role of source availability and hydrologic connectivity on antecedent conditions and propose a conceptual framework to characterize system response to ECEs at the watershed scale. We present four case studies in detail that span a range of types of antecedent conditions and type of ECE to highlight important controls and feedbacks. Because ECEs have the potential to export large amounts of water and materials, their occurrence in sequence can disproportionately amplify the response. In fact, multiple events may not be considered extreme in isolation, but when they occur in close sequence they may lead to extreme responses in terms of both supply and transport capacity. Therefore, to advance our understanding of these complexities, we need continued development of a mechanistic understanding of how antecedent conditions set the stage for ECE response across multiple regions and climates, particularly since monitoring of these rare events is costly and difficult to obtain. Through focused monitoring of critical ecosystems during rare events we will also be able to extend and validate modeling studies. Cross-regional comparisons are also needed to define characteristics of resilient systems. These monitoring, modeling, and synthesis efforts are more critical than ever in light of changing climate regimes, intensification of human modifications of the landscape, and the disproportionate impact of ECEs in highly populated regions.

Biogeochemistry↗
USGS2013

The use of modeling and suspended sediment concentration measurements for quantifying net suspended sediment transport through a large tidally dominated inlet

Sediment exchange at large energetic inlets is often difficult to quantify due complex flows, massive amounts of water and sediment exchange, and environmental conditions limiting long-term data collection. In an effort to better quantify such exchange this study investigated the use of suspended sediment concentrations (SSC) measured at an offsite location as a surrogate for sediment exchange at the tidally dominated Golden Gate inlet in San Francisco, CA. A numerical model was calibrated and validated against water and suspended sediment flux measured during a spring–neap tide cycle across the Golden Gate. The model was then run for five months and net exchange was calculated on a tidal time-scale and compared to SSC measurements at the Alcatraz monitoring site located in Central San Francisco Bay ~ 5 km from the Golden Gate. Numerically modeled tide averaged flux across the Golden Gate compared well (r 2 = 0.86, p-value < 0.05) with 25 h low-pass filtered (tide averaged) SSCs measured at Alcatraz over the five month simulation period (January through April 2008). This formed a basis for the development of a simple equation relating the advective flux at Alcatraz with suspended sediment flux across the Golden Gate. Utilization of the equation with all available Alcatraz SSC data resulted in an average export rate of 1.2 Mt/yr during water years 2004 through 2010. While the rate is comparable to estimated suspended sediment inflow rates from sources within the Bay over the same time period (McKee et al., 2013-this issue), there was little variation from year to year. Exports were computed to be greatest during the wettest water year analyzed but only marginally so.

California↗
USGS2012

Predicting longshore gradients in longshore transport: the CERC formula compared to Delft3D

The prediction of longshore transport gradients is critical for forecasting shoreline change. We employ simple test cases consisting of shoreface pits at varying distances from the shoreline to compare the longshore transport gradients predicted by the CERC formula against results derived from the process-based model Delft3D. Results show that while in some cases the two approaches give very similar results, in many cases the results diverge greatly. Although neither approach is validated with field data here, the Delft3D-based transport gradients provide much more consistent predictions of erosional and accretionary zones as the pit location varies across the shoreface.

Conference Paper↗
USGS2012

Monitoring and modeling nearshore dredge disposal for indirect beach nourishment, Ocean Beach, San Francisco

Nearshore dredge disposal was performed during the summer of 2005 at Ocean Beach, San Francisco, CA, a high energy tidal and wave environment. This trial run was an attempt to provide a buffer to a reach of coastline where wave attack during the winter months has had a severe impact on existing sewage infrastructure. Although the subsequent beach response was inconclusive, after one year the peak of the disposal mound had migrated ~100 m toward the shore, providing evidence that annual dredge disposal at this site could be beneficial over the long-term by at the very least providing: 1) additional wave dissipation during storms 2) compatible sediment to feed nearshore bars, 3) sediment cover on an exposed sewage outfall pipe, and 4) a viable alternative to the shoaling offshore disposal site. Numerical modeling suggests that despite the strong tidal currents in the region, wave forcing is the dominant factor moving the sediment slowly toward shore, and placing sediment at just slightly shallower depths (e.g. < 8 m vs. > 9 m) in the future would have a more immediate impact.

California↗
USGS2012

Recent scientific advances and their implications for sand management near San Francisco, California: The influences of the ebb tidal delta

Recent research in the San Francisco, California, U.S.A., coastal region has identified the importance of the ebb tidal delta to coastal processes. A process-based numerical model is found to qualitatively reproduce the equilibrium size and shape of the delta. The ebb tidal delta itself has been contracting over the past century, and the numerical model is applied to investigate the sensitivity of the delta to changes in forcing conditions. The large ebb tidal delta has a strong influence upon regional coastal processes. The prominent bathymetry of the ebb tidal delta protects some of the coast from extreme storm waves, but the delta also focuses wave energy toward the central and southern portions of Ocean Beach. Wave focusing likely contributes to a chronic erosion problem at the southern end of Ocean Beach. The ebb tidal delta in combination with non-linear waves provides a potential cross-shore sediment transport pathway that probably supplies sediment to Ocean Beach.

California↗
USGS2007

Bed forms created by simulated waves and currents in a large flume

The morphology and evolution of bed forms created by combinations of waves and currents were investigated using an oscillating plate in a 4-m-wide flume. Current speed ranged from 0 to 30 cm/s, maximum oscillatory velocity ranged from 20 to 48 cm/s, oscillation period was 8 s (except for one run with 12 s period), and the median grain size was 0.27 mm. The angle between oscillations and current was 90°, 60°, or 45°. At the end of each run the sand bed was photographed and ripple dimensions were measured. Ripple wavelength was also determined from sonar images collected throughout the runs. Increasing the ratio of current to wave (i.e., oscillatory) velocity decreased ripple height and wavelength, in part because of the increased fluid excursion during the wave period. Increasing the ratio of current to waves, or decreasing the angle between current and waves, increased the three-dimensionality of bed forms. During the runs, ripple wavelength increased by a factor of about 2. The average number of wave periods for evolution of ripple wavelength to 90% of its final value was 184 for two-dimensional ripples starting from a flat bed. Bed form orientations at the end of each run were compared to four potential controlling factors: the directions of waves, current, maximum instantaneous bed shear stress, and maximum gross bed form normal transport (MGBNT). The directions of waves and of MGBNT were equally good predictors of bed form orientations, and were significantly better than the other two factors.

Journal of Geophysical Research C: Oceans↗
USGS2007

An efficient mode-splitting method for a curvilinear nearshore circulation model

A mode-splitting method is applied to the quasi-3D nearshore circulation equations in generalized curvilinear coordinates. The gravity wave mode and the vorticity wave mode of the equations are derived using the two-step projection method. Using an implicit algorithm for the gravity mode and an explicit algorithm for the vorticity mode, we combine the two modes to derive a mixed difference–differential equation with respect to surface elevation. McKee et al.'s [McKee, S., Wall, D.P., and Wilson, S.K., 1996. An alternating direction implicit scheme for parabolic equations with mixed derivative and convective terms. J. Comput. Phys., 126, 64–76.] ADI scheme is then used to solve the parabolic-type equation in dealing with the mixed derivative and convective terms from the curvilinear coordinate transformation. Good convergence rates are found in two typical cases which represent respectively the motions dominated by the gravity mode and the vorticity mode. Time step limitations imposed by the vorticity convective Courant number in vorticity-mode-dominant cases are discussed. Model efficiency and accuracy are verified in model application to tidal current simulations in San Francisco Bight.

Coastal Engineering↗
USGS2007

Coastal processes study at Ocean Beach, San Francisco, CA: Summary of data collection 2004-2006

Ocean Beach in San Francisco, California, contains a persistent erosional section in the shadow of the San Francisco ebb tidal delta and south of Sloat Boulevard that threatens valuable public infrastructure as well as the safe recreational use of the beach. Coastal managers have been discussing potential mediation measures for over a decade, with little scientific research available to aid in decision making. The United States Geological Survey (USGS) initiated the Ocean Beach Coastal Processes Study in April 2004 to provide the scientific knowledge necessary for coastal managers to make informed management decisions. This study integrates a wide range of field data collection and numerical modeling techniques to document nearshore sediment transport processes at the mouth of San Francisco Bay, with emphasis on how these processes relate to erosion at Ocean Beach. The Ocean Beach Coastal Processes Study is the first comprehensive study of coastal processes at the mouth of San Francisco Bay.

California↗
USGS2007

Seabed ripple morphology and surficial sediment size at the SAX04 experiments near Fort Walton Beach, Florida, fall 2004

Data presented in this report originates from measurements obtained off the Florida coast (fig. 1) as part of the Sediment Acoustics Experiment (SAX04) and Ripples Department Research Initiative (DRI) (Office of Naval Research (ONR), Critical Benthic Environmental Processes and Modeling, Long Range BAA 04-001, Sept. 10, 2003). The aim of this document is to present methods employed to extract data and the resulting measured ripple characteristics (ripple height, wavelength, and orientation) and seabed grain sizes. Application and analysis of the data with respect to hydro- and morphodynamics will be addressed in subsequent reports. Sediment transport in the coastal region is a complex process involving interactions between flow dynamics, sediments, and bedforms. Sediment type and bed geometry directly influence entrainment of sediments into suspension, and at sites where ripples occur (sand formations on the order of several cm high and less than two meter long wavelengths), the understanding of ripple dynamics is an essential component in improving sediment transport models. To gain a better understanding and ability to predict sediment transport, a field study was undertaken to investigate morphology, orientation, and dynamics of ripples on the seafloor. The data obtained from the field campaign also supports an on-going effort to study the effects of ripples on low grazing acoustic penetration into sandy marine sediments for the detection of objects, such as mines (Jackson and others, 2002).

Florida↗
USGS2007

Coupling alongshore variations in wave energy to beach morphologic change using the SWAN wave model at Ocean Beach, San Francisco, CA

Coastal managers have faced increasing pressure to manage their resources wisely over the last century as a result of heightened development and changing environmental forcing. It is crucial to understand seasonal changes in beach volume and shape in order to identify areas vulnerable to accelerated erosion. Shepard (1950) was among the first to quantify seasonal beach cycles. Sonu and Van Beek (1971) and Wright et al. (1985) described commonly occurring beach states. Most studies utilize widest spaced 2-D cross shore profiles or shorelines extracted from aerial photographs (e.g. Winant et al. 1975; Aubrey, 1979, Aubrey and Ross, 1985; Larson and Kraus, 1994; Jimenez et al., 1977; Lacey and Peck, 1998; Guillen et al., 1999; Norcorss et al., 2002) to analyzed systematic changes in beach evolution. But with the exception of established field stations, such as Duck, NC (Birkemeier and Mason, 1984), ans Hazaki Oceanographical Research Station (HORS) in Japan (Katoh, 1997), there are very few beach change data sets with high temporal and spatial resolutions (e.g. Dail et al., 2000; Ruggiero et al., 2005; Yates et al., in press). Comprehensive sets of nearshore morphological data and local in situ measurements outside of these field stations are very rare and virtually non-existent high-energy coasts. Studied that have attempted to relate wave statistics to beach morphology change require some knowledge of the nearshore wave climate, and have had limited success using offshore measurement (Sonu and Van Beek, 1971; Dail et al., 2000). The primary objective of this study is to qualitatively compare spatially variable nearshore wave predictions to beach change measurements in order to understand the processes responsible for a persistent erosion 'hotspot' at Ocean Beach, San Francisco, CA. Local wave measurements are used to calibrate and validate a wave model that provides nearshore wave prediction along the beach. The model is run for thousands of binned offshore wave conditions to help isolate the effects of offshore wave direction and period on nearshore wave predictions. Alongshore varying average beach change statistics are computed at specific profile locations from topographic beach surveys and lidar data. The study area is located in the San Francisco Bight in central California. Ocean Beach is a seven kilometer long north-south trending sandy coastline located just south of the entrance to the San Francisco Bay Estuary (Figure 1). It contains an erosion hotspot in the southern part of the beach which has resulted in damage to local infrastructure and is the cause of continued concern. A wide range of field data collection and numerical modeling efforts have been focused here as part of the United States Geological Survey's (USGS) San Francisco Bight Coastal Processes Study, which began in October 2003 and represents the first comprehensive study of coastal processes at the mouth of San Francisco Bay. Ocean Beach is exposed to very strong tidal flows, with measured currents often in excess of 1 m/s at the north end of the beach. Current profiler measurements indicate that current magnitudes are greater in the northern portion of the beach, while wave energy is greater in the southern portion where erosion problems are greatest (Barnard et al., 2007). The sub-aerial beach volume fluctuates seasonally over a maximum envelope of 400,000 m 3 for the seven kilometer stretch (Barnard et al, 2007). The wave climate in the region is dominated by an abundance of low frequency energy (greater than 20 s period) and prevailing northwest incident wave angles. The application of a wave model to the region is further complicated by the presence of the Farallon Islands 40 kilometers west, and a massive ebb tidal delta at the mouth of San Francisco Bay (~150 km 2 ), which creates complicated refraction patterns as wave energy moves from offshore Ocean Beach; however the cost and threat of the energetic nearshore environment have limited the temporal and spatial resolution of these measurements. Applying numerical models to predict wave and current patterns along the beach can help supplement the filed data that exists and provide opportunities to make prediction about the impacts of changing environmental forcing.

California↗
USGS2007

Morphological evolution in the San Francisco Bight

San Francisco Bight, located near the coast of San Francisco, USA, is an extremely dynamic tidal inlet environmental subject to large waves and strong currents. Wave heights coming from the Pacific Ocean commonly exceed 5 m during winter storms. During peak flow tidal currents approach 3 m/s at the Golden Gate, a 1 km wide entrance that connects San Francisco Bay to the Pacific Ocean. Flow structure in this region varies markedly spatially and temporally due to the complex interaction by wind, waves and tidal currents. A multibeam sonar survey was recently completed that mapped in high resolution, for the first time, the bottom morphology in the region of the ebb tidal delta. This data set includes a giant sand wave field covering an area of approximately 4 square kilometers. The new survey enables the calculation of seabed change that has occurred in the past 50 years, since the last comprehensive survey of the area was completed. This comparison indicates an average erosion of 60 centimeters which equates to a total volume change of approximately 9.3 x 10 7 m 3 . Morphologic change also indicates that flood channels have filled and that the entire ebb delta is contracting radially.

California↗
USGS2006

Coastal monitoring of the May 2005 dredge disposal offshore of Ocean Beach, San Francisco, Calif.

Ocean Beach, California, contains an erosion hot spot in the shadow of the San Francisco ebb tidal delta south of Sloat Boulevard that threatens valuable public infrastructure as well as the safe recreational use of the beach. In an effort to reduce the erosion at this location and avoid hazardous navigation conditions at the current disposal site (SF-8), a new plan for the management of sediment dredged annually from the main shipping channel at the mouth of Francisco Bay was implemented in May 2005 by the United States Army Corps of Engineers, San Francisco District (COE). The objective for COE was to perform a test dredge disposal of ~230,000 m 3 (300,000 yd 3 ) of sand just offshore of the erosion hot spot, in depths between approximately 9 and 14 m. This disposal site was chosen because it is in a location where the strong tidal currents associated with the mouth of San Francisco Bay and waves can potentially feed sediment toward the littoral zone in the reach of the beach that is experiencing critical erosion. The onshore migration of sediment from the target disposal location might feed the primary longshore bar or the nearshore zone, and provide a buffer to erosion that peaks during winter months when large waves impact the region. The U.S. Geological Survey (USGS), in collaboration with the Sea Floor Mapping Lab (SFML) of California State University, Monterey Bay, monitored the initial bathymetric evolution of the test dredge disposal site and the adjacent coastal region from May 2005 to November 2005. This paper reports on this monitoring effort and assesses the short-term coastal response.

California↗
USGS2004

Suspended sediment and hydrodynamics above mildly sloped long wave ripples

We investigate the spatial and temporal distribution of suspended sediment and the associated hydrodynamics over mildly sloped long wave ripples on the inner shelf. These bedforms had wavelengths of approximately 1 m and heights of approximately 5 cm, in a mean water depth of 4 m. The vertical and temporal structures of the suspended sediment concentration (SSC) are consistent with the entrainment of sediment on the offshore flank of the ripple, and rapid vertical mixing at the time of flow reversal, followed by advection onshore by the onshore fluid motion. This work confirms that the mechanism for sediment suspension above low-amplitude, long wave ripples is similar to the vortex formation process expected over steeper vortex ripples. Numerical simulations of the flow using the Dune2d model indicate that a separated rotational flow structure is generated at the flank of the ripple on the seaward side of the ripple crest, near the time of flow reversal. The simulations indicate that only one vortex is formed during each wave period, in agreement with the field observations. This asymmetry is due mainly to the presence of an offshore mean near-bed current of approximately 6 to 8 cm/s. The SSC is calculated by the model and compared to the field observations. A hydraulic bed roughness of 10 to 15 median grain diameters ( d 50 ) was used in order to match the model prediction to the observed SSC approximately 1 cm above the seabed (cab). However, the modeled SSC and turbulent kinetic energy were significantly lower than the field observations at elevations exceeding approximately 2 cab.

North Carolina↗
USGS2004

One-dimensional wave bottom boundary layer model comparison: Specific eddy viscosity and turbulence closure models

Six one-dimensional-vertical wave bottom boundary layer models are analyzed based on different methods for estimating the turbulent eddy viscosity: Laminar, linear, parabolic, k —one equation turbulence closure, k−ε —two equation turbulence closure, and k−ω —two equation turbulence closure. Resultant velocity profiles, bed shear stresses, and turbulent kinetic energy are compared to laboratory data of oscillatory flow over smooth and rough beds. Bed shear stress estimates for the smooth bed case were most closely predicted by the k−ω model. Normalized errors between model predictions and measurements of velocity profiles over the entire computational domain collected at 15° intervals for one-half a wave cycle show that overall the linear model was most accurate. The least accurate were the laminar and k−ε models. Normalized errors between model predictions and turbulence kinetic energy profiles showed that the k−ω model was most accurate. Based on these findings, when the smallest overall velocity profile prediction error is required, the processing requirements and error analysis suggest that the linear eddy viscosity model is adequate. However, if accurate estimates of bed shear stress and TKE are required then, of the models tested, the k−ω model should be used.

Journal of Waterway, Port, Coastal and Ocean Engin↗