Evaluation of the bank stability and toe erosion model (BSTEM) for predicting lateral retreat on composite streambanks

Streambank erosion is known to be a major source of sediment in streams and rivers. The Bank Stability and Toe Erosion Model (BSTEM) was developed in order to predict streambank retreat due to both fluvial erosion and geotechnical failure. However, few, if any, model evaluations using long-term streambank retreat data have been performed. The objectives of this research were to (1) monitor long-term composite streambank retreat during a hydraulically active period on a rapidly migrating stream, (2) evaluate BSTEM’s ability to predict the measured streambank retreat, and (3) assess the importance of accurate geotechnical, fluvial erosion, and near-bank pore-water pressure properties. The Barren Fork Creek in northeastern Oklahoma laterally eroded 7.8 to 20.9 m along a 100-m length of stream between April and October 2009 based on regular bank location surveys. The most significant lateral retreat occurred in mid- to late-May and September due to a series of storm events, and not necessarily the most extreme events observed during the monitoring period. BSTEM (version 5.2) was not originally programmed to run multiple hydrographs iteratively, so a subroutine was written that automatically input the temporal sequence of stream stage and to lag the water table in the near-bank ground water depending on user settings. Eight BSTEM simulations of the Barren Fork Creek streambank were performed using combinations of the following input data: with and without a water table lag; default BSTEM geotechnical parameters (moderate silt loam) versus laboratory measured geotechnical parameters based on direct shear tests on saturated soil samples; and default BSTEM fluvial erosion parameters versus field measured fluvial erosion parameters from submerged jet tests. Using default BSTEM input values underestimated the actual erosion that occurred. Lagging the water table predicted more geotechnical failures resulting in greater streambank retreat. Using measured fluvial and geotechnical parameters and a water table lag also under predicted retreat (approximately 3.3 m), but did predict the appropriate timing of streambank collapses. The under prediction of retreat was hypothesized to be due to over predicting the critical shear stress of the non-cohesive gravel, under predicting the erodibility of the non-cohesive gravel, and/or under predicting the imposed shear stress acting on the streambank. Current research improving our understanding of shear stress distributions, streambank pore-water pressure dynamics, and methods for estimating excess shear stress parameters for noncohesive soils will be critical for improving BSTEM and other streambank stability models

Evaluation of the bank stability and toe erosion model (BSTEM) for predicting lateral retreat on composite streambanks

Streambank erosion is known to be a major source of sediment in streams and rivers. The Bank Stability and Toe Erosion Model (BSTEM) was developed in order to predict streambank retreat due to both fluvial erosion and geotechnical failure. However, few, if any, model evaluations using long-term streambank retreat data have been performed. The objectives of this research were to (1) monitor long-term composite streambank retreat during a hydraulically active period on a rapidly migrating stream, (2) evaluate BSTEM’s ability to predict the measured streambank retreat, and (3) assess the importance of accurate geotechnical, fluvial erosion, and near-bank pore-water pressure properties. The Barren Fork Creek in northeastern Oklahoma laterally eroded 7.8 to 20.9 m along a 100-m length of stream between April and October 2009 based on regular bank location surveys. The most significant lateral retreat occurred in mid- to late-May and September due to a series of storm events, and not necessarily the most extreme events observed during the monitoring period. BSTEM (version 5.2) was not originally programmed to run multiple hydrographs iteratively, so a subroutine was written that automatically input the temporal sequence of stream stage and to lag the water table in the near-bank ground water depending on user settings. Eight BSTEM simulations of the Barren Fork Creek streambank were performed using combinations of the following input data: with and without a water table lag; default BSTEM geotechnical parameters (moderate silt loam) versus laboratory measured geotechnical parameters based on direct shear tests on saturated soil samples; and default BSTEM fluvial erosion parameters versus field measured fluvial erosion parameters from submerged jet tests. Using default BSTEM input values underestimated the actual erosion that occurred. Lagging the water table predicted more geotechnical failures resulting in greater streambank retreat. Using measured fluvial and geotechnical parameters and a water table lag also under predicted retreat (approximately 3.3 m), but did predict the appropriate timing of streambank collapses. The under prediction of retreat was hypothesized to be due to over predicting the critical shear stress of the non-cohesive gravel, under predicting the erodibility of the non-cohesive gravel, and/or under predicting the imposed shear stress acting on the streambank. Current research improving our understanding of shear stress distributions, streambank pore-water pressure dynamics, and methods for estimating excess shear stress parameters for noncohesive soils will be critical for improving BSTEM and other streambank stability models

Escherichia coli Transport from Surface-Applied Manure to Subsurface Drains through Artificial Biopores

Bacteria transport in soils primarily occurs through soil mesopores and macropores (e.g., biopores and cracks). Field research has demonstrated that biopores and subsurface drains can be hydraulically connected. This research was conducted to investigate the importance of surface connected and disconnected (buried) biopores on Escherichia coli (E. coli) transport when biopores are located near subsurface drains. A soil column (28 by 50 by 95 cm) was packed with loamy sand and sandy loam soils to bulk densities of 1.6 and 1.4 Mg m−3, respectively, and containing an artificial biopore located directly above a subsurface drain. The sandy loam soil was packed using two different methods: moist soil sieved to 4.0 mm and air-dried soil manually crushed and then sieved to 2.8 mm. A 1-cm constant head was induced on the soil surface in three flushes: (i) water, (ii) diluted liquid swine (Sus scrofa) manure 48 h later, and (iii) water 48 h after the manure. Escherichia coli transport to the drain was observed with either open surface connected or buried biopores. In surface connected biopores, E. coli transport was a function of the soil type and the layer thickness between the end of the biopore and drain. Buried biopores contributed flow and E. coli in the less sorptive soil (loamy sand) and the sorptive soil (sandy loam) containing a wide (i.e., with mesopores) pore space distribution prevalent due to the moist soil packing technique. Biopores provide a mechanism for rapidly transporting E. coli into subsurface drains during flow events

Role of Directly Connected Macropores on Pathogen Transport to Subsurface Drainage Water

Pathogen contamination of water supplies is now considered one of the top water quality issues in the United States and worldwide. Continual application of livestock manure may contribute to nonpoint source pollution by releasing microbial pathogens including bacteria, virus, and protozoa, through runoff and subsurface drainage water to surface and ground water. Many studies have been conducted in the laboratories and fields to understand the preferential flow through macropores. But no experiments in the field have been conducted to examine the breakthrough curve of pathogen and/or Escherichia coliform (E.coli) with directly connected macropores. The objective of this research is to address the transport of pathogens (specifically the indicator organism E. coli) through soils, and more specifically the role of macropores in the transport of E. coli to subsurface drains. A greater understanding and more theoretical modeling approach is needed to understand the role of directly connected macropores on pathogen transport to subsurface drainage

A new adaptive neural network and heuristics hybrid approach for job-shop scheduling

Copyright @ 2001 Elsevier Science LtdA new adaptive neural network and heuristics hybrid approach for job-shop scheduling is presented. The neural network has the property of adapting its connection weights and biases of neural units while solving the feasible solution. Two heuristics are presented, which can be combined with the neural network. One heuristic is used to accelerate the solving process of the neural network and guarantee its convergence, the other heuristic is used to obtain non-delay schedules from the feasible solutions gained by the neural network. Computer simulations have shown that the proposed hybrid approach is of high speed and efficiency. The strategy for solving practical job-shop scheduling problems is provided.This work is supported by the National Nature Science Foundation (No. 69684005) and National High -Tech Program of P. R. China (No. 863-511-9609-003)

Comparison of Aquifer Sustainability Under Groundwater Administrations in Oklahoma and Texas

We compared two approaches to administration of groundwater law on a hydrologic model of the North Canadian River, an alluvial aquifer in northwestern Oklahoma. Oklahoma limits pumping rates to retain 50% aquifer saturated thickness after 20 years of groundwater use. The Texas Panhandle Groundwater Conservation District’s (GCD) rules limit pumping to a rate that consumes no more than 50% of saturated thickness in 50 years, with reevaluation and readjustment of permits every 5 years. Using a hydrologic model (MODFLOW), we simulated river-groundwater interaction and aquifer dynamics under increasing levels of ‘‘development’’ (i.e., increasing groundwater withdrawals). Oklahoma’s approach initially would limit groundwater extraction more than the GCD approach, but the GCD approach would be more protective in the long run. Under Oklahoma rules more than half of aquifer storage would be depleted when development reaches 65%. Reevaluation of permits under the Texas Panhandle GCD approach would severely limit pumping as the 50% level is approached. Both Oklahoma and Texas Panhandle GCD approaches would deplete alluvial base flow at approximately 10% development. Results suggest periodic review of permits could protect aquifer storage and river base flow. Modeling total aquifer storage is more sensitive to recharge rate and aquifer hydraulic conductivity than to specific yield, while river leakage is most sensitive to aquifer hydraulic conductivity followed by specific yield

Reservoir Sedimentation and Upstream Sediment Sources: Perspectives and Future Research Needs on Streambank and Gully Erosion

Citation: Fox, G.A., Sheshukov, A., Cruse, R. et al. Environmental Management (2016) 57: 945. doi:10.1007/s00267-016-0671-9The future reliance on water supply and flood control reservoirs across the globe will continue to expand, especially under a variable climate. As the inventory of new potential dam sites is shrinking, construction of additional reservoirs is less likely compared to simultaneous flow and sediment management in existing reservoirs. One aspect of this sediment management is related to the control of upstream sediment sources. However, key research questions remain regarding upstream sediment loading rates. Highlighted in this article are research needs relative to measuring and predicting sediment transport rates and loading due to streambank and gully erosion within a watershed. For example, additional instream sediment transport and reservoir sedimentation rate measurements are needed across a range of watershed conditions, reservoir sizes, and geographical locations. More research is needed to understand the intricate linkage between upland practices and instream response. A need still exists to clarify the benefit of restoration or stabilization of a small reach within a channel system or maturing gully on total watershed sediment load. We need to better understand the intricate interactions between hydrological and erosion processes to improve prediction, location, and timing of streambank erosion and failure and gully formation. Also, improved process-based measurement and prediction techniques are needed that balance data requirements regarding cohesive soil erodibility and stability as compared to simpler topographic indices for gullies or stream classification systems. Such techniques will allow the research community to address the benefit of various conservation and/or stabilization practices at targeted locations within watersheds

Field evidence of a natural capillary barrier in a gravel alluvial aquifer

Ozark streams commonly feature “composite” floodplains, in which the vadose zone consists of silt or silt loam soils (?1 m thick) overlying gravel subsoil. Previous work has shown that preferential flow paths can exist within the gravel subsoil, which can conduct water and P at rates exceeding the sorption capacity of the gravel. At a site on Barren Fork Creek, a 1- by 1-m infiltration plot was constructed and an infiltration experiment was performed using sequentially introduced solutes including P (the constituent of regulatory interest), Rhodamine-WT (Rh-WT, a visual tracer), and Cl− (an electrical tracer). The solute transport was measured with monitoring wells (MWs) placed 1 m from the plot boundary and 5 m down the groundwater flow gradient using an electrical resistivity imaging (ERI) array. The ERI method utilized differences between a pre-infiltration background image and subsequent temporal images taken during the test to quantify changes induced by the tracers. The infiltration test maintained a steady-state flow rate of 4.5 L min−1 for 84.75 h. Electrical resistivity imaging data showed significant changes in resistivity induced by the tracers within the soil vadose zone under the plot but no similar changes within the gravel, indicating that the interface was acting as a capillary barrier. Electrical resistivity images 5 m away from the plot showed tracer breakthrough into the gravel in areas not sampled by the MWs. Solute detection was limited in MWs, indicating that MWs could not adequately monitor movement below the capillary barrier because it controlled migration of solute to the heterogeneous phreatic zone

E. coli Transport through Surface-Connected Biopores Identified from Smoke Injection Tests

Macropores are the primary mechanism by which fecal bacteria from surface-applied manure can be transported into subsurface drains or shallow groundwater bypassing the soil matrix. Limited research has been performed investigating fecal bacteria transport through specific macropores identified in the field. The objective of this research was to better understand how fecal bacteria, using Escherichia coli (E. coli) as an indicator organism, are transported through naturally occurring macropores and potential interactions between the macropore and soil matrix domains in the field under controlled experimental conditions. Direct injection/infiltration tests were conducted in two naturally occurring, surface-connected macropores (biopores) that penetrated to the subsurface drain depth, as identified by smoke tests. Data included total drain flow rate (baseflow rate and biopore flow rate), biopore inflow rate, and Rhodamine WT and E. coli concentrations in the drains. Analysis techniques included determining increases in subsurface drain flow rates due to the infiltration tests and percentage of the injected concentration reaching the subsurface drains after dilution with the drain baseflow. In the absence of data for mechanistic models, empirically based rational polynomial models were compared to the more commonly utilized lognormal distribution for modeling the load rate breakthrough curves. Load estimates were derived from integrated forms of these empirical functions, and percent reductions were calculated for Rhodamine WT and E. coli. Peak total drain flow rates increased nearly two-fold due to direct injection into the biopores. Less than 25% of the initial concentrations injected into the biopores reached the drain after dilution with the baseflow in the drain. Lognormal distributions best fit the Rhodamine WT load rate breakthrough curves (R2 = 0.99 for both biopores) and the E. coli load rate data for one of the biopores (R2 = 0.98). A rational fractional polynomial model that tailed off more slowly best fit the E. coli load rate data for the other biopore (R2 = 0.98). Approximately one log reduction was estimated for E. coli loads due to interaction with the soil profile as water flowed through the tortuous path of the biopores; in other words, the soil surrounding the biopore filtered approximately 90% of the E. coli load that entered the biopore compared to approximately 75% for Rhodamine WT. Considering that applied animal manure can contain millions of bacteria per mL, high concentrations and loads are still possible in the subsurface drain flow if macropores are present