Submerged Jet Test Research Articles

Riverbank retreat analysis of the U-Tapao River, southern Thailand

Riverbank retreat is a result of complex combinations of several processes, including subaerial processes, fluvial erosion, and bank failure. The objective of this study was to analyze riverbank retreat of six representative riverbanks along the U-Tapao River in southern Thailand using a process-based riverbank retreat model. Field and laboratory tests were conducted to determine index and engineering properties of the riverbank soil required in the modeling. In particular, the erodibility parameters of the riverbank soil were estimated using empirical formulae, measured in situ by performing a submerged jet test, and estimated from long-term bank retreat simulations using the Bank Stability and Toe Erosion Model (BSTEM) incorporated with a lumped adjustment factor. The observed bank retreat over the period from 2002 to 2016 obtained from analysis of aerial imagery was used to verify the validity of the riverbank retreat results. Good agreement with the observations was obtained from BSTEMs using adjusted erodibility parameters.

Effect of Water Potential and Void Ratio on Erodibility for Agricultural Soils

Core Ideas:Critical shear stress can be modeled by silt content, void ratio and water potential.Erodibility can be predicted by critical shear stress, clay content and void ratio.Bulk density displayed a convex trend as antecedent soil moisture increasing.Soil erodibility has confounded researchers for decades. Difficulties arise with initiation of motion, pore‐water status, physical, and perhaps biological, material properties and type of applied energy (i.e., rainfall, runoff, freezing or thawing, wind). Though specific tests have been developed to determine critical shear stress and soil erodibility, solutions do not seem to conform to theory. We have models for erosion assessment and, although each provides practical information for planning and management, all share a need to improve predictions for soil detachment. Here, a series of submerged jet tests (JET) are performed on samples of three soils prepared to represent agricultural conditions (i.e., modest bulk density), five initial soil water contents are imposed during sample packing that affected soil void ratio, and four water potential gradients are imposed during jet testing. Results, for both coarse‐ and fine‐grained soils, indicate that critical shear stress can be predicted with knowledge of the silt content, void ratio and water potential gradient, and soil erodibility can be predicted with knowledge of critical shear stress, clay content and void ratio. This study was limited by the number of soils examined; however, the results are thought provoking.

JET EROSION DEVICE (JED) – MEASUREMENT OF SOIL ERODIBILITY COEFFICIENTS

Erosion from riverbank is most properly represented by the erodibility factor. One of the methods that can be used for in situ soil erodibility testing is the submerged jet test called Jet Erosion Test (JET). In this study, a newly modified version of the JET device namely Jet Erosion Device (JEd) is fabricated, with improved features and design that facilitates testing in the field and the laboratory. Analysis and calibration of the JEd tests were conducted to check on the reliability and performance of the Jet Erosion Device (JEd). Some preliminary results were shown to give some insights on the capabilities of the JEd. An evaluation of the erosion performance index i.e. jet index was performed to characterize the erosion resistance. The estimation of erodibility coefficients were made using the results of jet index obtained.

EROSION PROCESSES IN COMPOSITE RIVERBANKS: EXPERIMENTS AND MODELLING

Erosion processes in a composite bank is a very complex phenomenon due to many factors involved such as: seepage, variability of the bank stratifications, river stage variations, fluvial processes, soil stabilities. This study was focused to understand the primary processes responsible for bank erosion, and methodology to predict the bank erosion. Finally, a stochastic bank erosion model is proposed to estimate the seasonal bank erosion in a composite river bank. In the first stage, the developed model was simulated with known stage hydrograph, bank soil erodibility, and the bank stratification of a river bend in a reach of the Brahmaputra River in India. The critical shear stresses of the bank soils were determined through submerged-jet tests and the seepage erosion parameters were determined through laboratory lysimeter experiments. The predicted seasonal bank erosion rates for four consecutive years were compared with the observed rates. The results showed a good agreement between the observed data and modelling results. In the second stage, the uncertainty in the stage hydrograph, soil erodibility and the bank stratifications were considered. The stochastic bank erosion predictions were compared with the observed distribution of the bank erosion in 45 bends of the Brahmaputra River over 700 km long reach. Since the model has predicted satisfactorily therefore, the developed model can be used to obtain morphological dynamics of a sand-bed river bend with composite banks.

Determination of critical shear stress of non‐cohesive soils using submerged jet test and turbulent kinetic energy

AbstractLaboratory tests using Jet Erosion Testing (JET) apparatus, impinging normally on a horizontal boundary, were conducted to determine the critical shear stress (τc) of non‐cohesive soil samples. A three‐dimensional (3D) SonTek/YSI 16 MHz Micro‐Acoustic Doppler Velocimeter (MicroADV) was used to measure turbulent kinetic energy (TKE) at a radial limit of entrainment in the wall jet zone and the measurements were used to calculate τc of the samples. The results showed that TKE increases exponentially with increasing particle size. The τc from this study were comparable (R2 = 0.8) to the theoretical τc from Shields diagram after bed roughness scale ratio (D/ks), due to the non‐uniform bed conditions, was accounted for. This study demonstrated that JET and TKE can be used to determine τc of non‐cohesive soils. The use of JET and TKE was found to be faster and easier when compared to the conventional approach of using flumes. A relationship of TKE at the onset of incipient motion (TKEc) and samples’ D50 developed in this study can be used to predict τc of non‐cohesive soils under similar non‐uniform conditions. Copyright © 2015 John Wiley & Sons, Ltd.

Stochastic erosion of composite banks in alluvial river bends

AbstractThe erosion of composite river banks is a complex process involving a number of factors including fluvial erosion, seepage erosion, and cantilever mass failure. To predict the rate of bank erosion with these complexities, a stochastic bank erosion model is suitable to define the probability distribution of the controlling variables. In this study, a bank erosion model in a river bend is developed by coupling several bank erosion processes with an existing hydrodynamic and morphological model. The soil erodibility of cohesive bank layers was measured using a submerged jet test apparatus. Seasonal bank erosion rates for four consecutive years at a bend in the Brahmaputra River, India, were measured by repeated bankline surveys. The ability of the model to predict erosion was evaluated in the river bend that displayed active bank erosion. In this study, different monsoon conditions and the distribution functions of two variables were considered in estimating the stochastic bank erosion rate: the probability of the soil erodibility and stochastic stage hydrographs for the nth return period river stage. Additionally, the influences of the deflection angle of the streamflow, longitudinal slope of river channel, and bed material size on bank erosion rate were also investigated. The obtained stochastic erosion predictions were compared with the observed distribution of the annual‐average bank erosion rate of 45 river bends in the Brahmaputra River. The developed model appropriately predicted the short‐term morphological dynamics of sand‐bed river bends with composite banks. Copyright © 2014 John Wiley & Sons, Ltd.

Measuring Soil Erodibility Using a Laboratory “Mini” JET

Abstract. Typically soil erodibility is quantified using an excess shear stress equation, dependent on two major soil parameters: the critical shear stress (I„ c ) and the erodibility coefficient (k d ). A submerged jet test (JET, Jet Erosion Test) is one method that has been developed and methodology of use established in the literature for measuring these parameters. In this study, a new miniature version of the JET device (“mini” JET), with the advantage of being easier to use in the field, was used to measure I„ c and k d for two soils (silty sand and clayey sand), and results were compared to the larger original laboratory JET. The objective of this research was to determine if the “mini” JET measured equivalent values for I„ c and k d compared to the original JET device. In-order to compare the performance and repeatability of both JET devices, tests were performed on paired samples prepared in the same way and tested at the same time. Samples of the soils tested were prepared at different water contents with a standard compaction effort of 600 kN-m/m 3 (ASTM). Some variability in measuring I„ c and k d was observed between paired samples due to variability in the soil texture of the soil samples and differences in soil moisture levels. The k d values measured by the two JET devices for both soils were not significantly different. The I„ c values measured by the “mini” JET were consistently lower than those measured by the original JET. This was hypothesized to be due to the structure of the soil sample due to the compaction method and the procedure utilized to determine I„ c . Adjustment of the equilibrium depth of the “mini” JET resulted in small differences in the estimated I„ c between both JET devices. Both JET devices also demonstrated consistent performance in measuring I„ c -k d relationships, which were compared with those observed in previous field research.

Deriving Parameters of a Fundamental Detachment Model for Cohesive Soils from Flume and Jet Erosion Tests

Abstract. The erosion rate of cohesive soils is commonly quantified using the excess shear stress model, which is dependent on two major soil parameters: the critical shear stress (I„ c ) and the erodibility coefficient (k d ). A submerged jet test (jet erosion test, or JET) is one method that has been developed for measuring these parameters. The disadvantage of using the excess shear stress model is that parameters I„ c and k d change according to erosion conditions, such as soil structure, soil orientation, type of clay, presence of roots, and seepage forces. A more mechanistically based detachment model, called the Wilson model, is proposed in this article for modeling the erosion rate of soils using hydraulic analysis of a JET. The general framework of the Wilson model is based on two soil parameters (b 0 and b 1 ). The objectives of this study were to: (1) develop methods of analysis of the JET to determine parameters b 0 and b 1 for the Wilson model in a similar fashion to the previous methodology developed for open-channel flow, and (2) compare the excess stress model parameter (k d ) and the Wilson model parameters (b 0 and b 1 ) determined from the flume tests and JETs for two cohesive soils. Flume tests, treated as the standard test method, and original and “mini” JETs were conducted on two soils to independently measure the excess shear stress model parameter (k d ) and the Wilson model parameters (b 0 and b 1 ). Soil samples of two cohesive soils (silty sand and clayey sand soils) were packed in a soil box for the flume tests and the JETs at water contents ranging from 8.7% to 18.1%. No statistically significant differences were observed for the excess shear stress model parameter (k d ) and for the Wilson model parameters (b 0 and b 1 ) when determined from the flume tests and JET devices, except for b 1 with the original JET. The Wilson model is advantageous in being a more mechanistic, fundamentally based erosion equation as compared to the excess shear stress model. The Wilson model can be used in place of the excess shear stress model with parameters that can be estimated using existing JET techniques.

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 20.9m 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 3.3m), 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.

STUDY ON EFFECT OF FACTORS ON CRITICAL SHEAR STRESS OF COHESIVE BANK MATERIALS FOR COASTAL EROSION

The aim of this study is to investigate effect of sand-silt-clay content, moisture content, salinity, consolidation, and vegetation density on critical shear stress (tc) of cohesive bank materials for erosion processes of rivers and coastal regions. The authors used the non-vertical submerged jet test apparatus designed by Hanson et al. (2002) and reproduced by Deguchi et al. (2007) to carry out both laboratory and in situ measurements. The laboratory experimental results showed that the tc increased as the rate of clay content, salinity, consolidation, and vegetation density increased. The t c decreased as the moisture content increased. The in situ experimental results of five severely eroded sites of the Soai Rap river banks, southern Hochiminh City were similar to thoses of laboratory experiments. The erodibility (kd) of cohesive bank material can also be determined when the t c is measured.

Erodibility of fine soil from the composite river bank of Brahmaputra in India

AbstractThe erosion of a composite river bank critically depends on the erodibility of its fine soils, as the fine soil has higher resistance against erosion. Therefore, for the estimation of the bank erosion in the case of a composite river bank, it is important to determine the critical shear stress and erodibility coefficients of the bank soil and their spatial distribution. In the present study, erodibility parameters of the river bank of Brahmaputra in India have been estimated through 58 in situ submerged jet tests. The significance of spatial and layer‐wise distribution of the erodibility parameters was tested through analysis of variance (ANOVA). Results indicate that the spatial variation of erodibility parameters is highly significant, but layer‐wise variations of the erodibility parameters are not significant. Therefore, the erodibility of the riverbank depends on the particular location, whereas layer‐wise average erodibility parameters can be lumped for the estimation of the bank erosion for the specific site. Using the measured erodibility parameters, yearly river bank erosions at the study locations were computed and found to fall within the reported range of the bank erosion in the Brahmaputra River. Copyright © 2010 John Wiley & Sons, Ltd.

Prediction of channel degradation rates in urbanizing watersheds

In urbanizing watersheds, as land use changes, and storm sewers and impervious surfaces are increased, both the frequency and magnitude of discharge increase, resulting in stream channel down-cutting and widening and related loss of structures and engineering works. A simple model for assessing the time rate of degradation in watersheds is given. The model relies on a continuous simulation of watershed discharge based on local climate (SWAT-DEG) instead of a dominant discharge approach. Unique to this approach is the use of in situ erosion parameters derived from submerged jet tests, which give both the allowable tractive force as well as erodibility coefficients. The model is used in concert with the Watson-Harvey analysis of channel evolution. Four methods were used to verify and validate the model for estimating rates of degradation. A case study of channel stability assessment using this tool was made in north central Texas (USA). Rates of incision were nonlinear and ranged from 0–76 mm/year.

Experimental Study on Critical Shear Stress of Cohesive Bed Materials for Erosion

The aim of the study is to investigate effects of sand-silt-clay content, moisture content, and salinity on critical shear stress (τc) of cohesive bed material for erosion. The authors used the non-vertical submerged jet test apparatus designed by Hanson et al.(2002) to carry out both laboratory and in situ measurements. Forty remolded samples were made with various sand-silt-clay content, moisture content and salinity. The laboratory experimental results showed that τc depended on the sand-silt-clay content, moisture content, and salinity. The τc increased when the rate of clay content increased. The value of τc decreased when the moisture content increased. The value of τc increased when the salinity increased. The results of five in situ experiments of the Soai Rap cohesive riverbanks, southern Viet Nam also showed that the value of τc also increased when the rate of clay content increased. The erodibility (kd) of cohesive bed material can also be determined when τc is measured.

Changes in streambank erodibility and critical shear stress due to subaerial processes along a headwater stream, southwestern Virginia, USA

Despite more than 40 yr of research attributing temporal changes in streambank erosion rates to subaerial processes, little quantitative information is available on the relationships between streambank erodibility ( k d) and critical shear stress ( τ c) and the environmental conditions and processes that enhance streambank erosion potential. The study goal was to evaluate temporal changes in k d and τ c from soil desiccation and freeze–thaw cycling. Soil erodibility and τ c were measured monthly in situ using a multiangle, submerged jet test device. Soil moisture, temperature, and bulk density as well as precipitation, air temperature, and stream stage were measured continuously to determine changes in soil moisture content and state. Pairwise Mann–Whitney tests indicted k d was 2.9 and 2.1 times higher ( p < 0.0065) during the winter (December–March) than in the spring/fall (April–May, October–November) and the summer (June–September), respectively. Regression analysis showed 80% of the variability in k d was explained by freeze–thaw cycling alone. Study results also indicated soil bulk density was highly influenced by winter weather conditions ( r 2 = 0.86): bulk density was inversely related to both soil water content and freeze–thaw cycling. Results showed that significant changes in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes. Water resource professionals should consider the implications of increased soil erodibility during the winter in the development of channel erosion models and stream restoration designs.

Methods for Determining Streambank Critical Shear Stress and Soil Erodibility: Implications for Erosion Rate Predictions

According to the U.S. EPA, excess sediment is a significant cause of water quality impairment for rivers. The goal of this study was to compare different methods of determining two parameters used to estimate streambank erosion, soil critical shear stress (t c) and soil erodibility (kd) and to determine the impact of those differences on predictions of streambank erosion. At 25 field sites, bank erosion tests were conducted using a submerged jet test device, and soil samples were collected. Critical shear stress was measured using a multi-angle submerged jet test device (JT) and estimated based on Shields' diagram (SD) and empirical relations based on the soil parameters, percent clay (Pc), plasticity index (Iw), particle size (D50) and percent silt-clay (SC). Additionally, using a single set of t c values, the kd measured by the jet test was compared to predictions from two empirical kd relations. Using these parameter values, streambank erosion rates were predicted for a local stream. The jet t c estimates were as much as four orders of magnitude greater than the SD, Pc, and D50 estimates, indicating the SD and empirical methods underestimate t c. The two empirical kd equations produced similar kd values that were generally two orders of magnitude less than the values from the jet test measurements. Erosion predictions followed the same trend as the kd data, with the jet test measurements resulting in higher predictions. Field validation of these methods over a wide range of soil types is recommended to develop methods of estimating kd and t c for fine-grained streambank soils.

THE EFFECTS OF VEGETATION AND SOIL TYPE ON STREAMBANK EROSION, SOUTHWESTERN VIRGINIA, USA1

ABSTRACT:The goal of this research was to evaluate the relative effects of root density, freeze/thaw cycling, and soil properties on the erodibility and critical shear stress of streambanks. The erodibility and critical shear stress of rooted bank soils were measured in situ at 25 field sites using a submerged jet test device; several soil, vegetation, and stream chemistry characteristics shown to influence soil erosion were also assessed. Multiple linear regression analysis was conducted to determine those factors that most influenced streambank erodibility and the relative impact of riparian vegetation. Study results indicated that soil erosion is a complex phenomenon that depends primarily on soil bulk density. Freeze/thaw cycling, soil antecedent moisture content, the density of roots with diameters of 2 to 20 mm, soil texture, and the interaction of soil pore water and stream water had a significant impact on soil erodibility and critical shear stress, depending on soil type. Riparian vegetation had multiple significant effects on soil erodibility. In addition to reducing soil erodibility through root reinforcement, the streamside vegetation affected soil moisture and altered the local microclimate, which in turn affected freeze/thaw cycling (FTC). This study represents the first in situ testing of the erodibility of vegetated streambanks and provides a quantitative analysis on the effects of vegetation on streambank erosion, relative to other soil physical and chemical parameters.

Prediction of Stream Channel Erosion Potential

Field tests using a submerged jet apparatus were conducted to determine the erodibility coefficients in alluvial soils along stream channels. The soils tested ranged from cohesive clay soils to non-cohesive sandy soils. In addition to performing the jet test at thirty sample sites, laboratory tests on soil samples taken from each site were done to determine soil bulk density, antecedent soil moisture, Atterburg limits, and grain size distribution. Regression analysis was performed on these parameters against the erodibility coefficient to assess whether laboratory testing could be used to extend the submerged jet test results upstream and downstream. Best results were obtained with equations stratified by percent clay and soil activity with multiple correlation coefficients ranging from 0.78 to 0.96. Preliminary efficiency of the equations was 64 percent (coefficient of determination .71) when compared to an independent data set. Use of the erosion coefficient in a stream channel degradation model is shown.

The Influence of Soil Moisture and Compaction on Spillway Erosion

Submerged jet tests were conducted on a soil material compacted by dynamic and static load methods over a range of dry unit weights and moisture contents. The compacted soil samples were pre-wet prior to testing. An index parameter was used to compare changes in the erosion resistance of the soil at different compacted dry unit weights and compacted moisture contents. Moisture content at the time of compaction had a significant influence on soil erosion resistance. Additionally, at a constant moisture content, the erosion resistance increased as the dry unit weight increased. These results, along with results of two compacted spillway channel tests on the same soil, suggest that proper compaction should be considered in the repair of earthen auxiliary spillways.

DEVELOPMENT OF A JET INDEX TO CHARACTERIZE EROSION RESISTANCE OF SOILS IN EARTHEN SPILLWAYS

ABSTRACT A soil parameter is developed based on concepts from local scour studies of non-cohesive and cohesive soils and the results of a site-specific submerged jet testing device. Submerged jet test results on four soils with a range of physical conditions are analyzed. The submerged jet had a nozzle diameter of 13 mm, and was set at a jet height of 0.22 m prior to testing the soil. The soils were tested over a range of jet velocities at the nozzle of 166 cm/s to 731 cm/s. The results indicate that erosion, expressed as the depth of scour divided by time, in the site-specific submerged jet testing device may be related to the jet velocity, a time function, and a soil parameter (jet index, Ji). The jet index is intended to provide a common method of expressing erosion resistance, to assist those who work with different soils and soil conditions for measurement and design, and possibly to develop performance and prediction relationships for earthen spillways.