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• 1. [Article] A Literature Review of the Beneficial Use of Dredged Material and Sediment Management Plans and Strategies

  This report identifies lessons learned from the body of existing literature on dredge sediment beneficial uses. It also examines the constructive role collaborative processes can play in development of ...

  Citation × Citation Citation Abstract Copy Title: A Literature Review of the Beneficial Use of Dredged Material and Sediment Management Plans and Strategies Author: Portland State University. Hatfield School of Government. Center for Public Service, Welch, Michelle, Mogren, Eric Thomas, Beeney, Lauren Year: 2016 This report identifies lessons learned from the body of existing literature on dredge sediment beneficial uses. It also examines the constructive role collaborative processes can play in development of sediment management plans. The authors reviewed approximately 100 documents and reports for this project. Seventeen of those were reviewed in detail based on their relevance in identifying sediment beneficial uses and/or the use of collaborative processes in the development of sediment management plans. A number of these documents were sediment management plans and strategies for specific projects and programs in other locations. The report presents findings and lessons for the consideration of regional stakeholders in development of sediment disposal plans. Title: A Literature Review of the Beneficial Use of Dredged Material and Sediment Management Plans and Strategies Author: Portland State University. Hatfield School of Government. Center for Public Service, Welch, Michelle, Mogren, Eric Thomas, Beeney, Lauren Year: 2016 This report identifies lessons learned from the body of existing literature on dredge sediment beneficial uses. It also examines the constructive role collaborative processes can play in development of sediment management plans. The authors reviewed approximately 100 documents and reports for this project. Seventeen of those were reviewed in detail based on their relevance in identifying sediment beneficial uses and/or the use of collaborative processes in the development of sediment management plans. A number of these documents were sediment management plans and strategies for specific projects and programs in other locations. The report presents findings and lessons for the consideration of regional stakeholders in development of sediment disposal plans. Close

• 2. [Article] Implementation of a Sediment Transport Model for CE-QUAL-W2

  The CE-QUAL-W2 model, developed by Portland State University, simulates water quality and flow. Recommendations to expand on this model and have it include sediment transport are implemented in this report. ...

  Citation × Citation Citation Abstract Copy Title: Implementation of a Sediment Transport Model for CE-QUAL-W2 Author: Hanna, Rachel Year: 2014 The CE-QUAL-W2 model, developed by Portland State University, simulates water quality and flow. Recommendations to expand on this model and have it include sediment transport are implemented in this report. Existing one-, two-, and three-dimensional models are reviewed and assessed for their sediment transport methodology. A laterally (width) averaged sediment concentration model is developed as an Upwind Center Space Scheme using CE-QUAL-W2 data. The scheme includes a method to calculate scour for sediment concentration and results of the model are shown for a simulated branch of the Spokane River. Title: Implementation of a Sediment Transport Model for CE-QUAL-W2 Author: Hanna, Rachel Year: 2014 The CE-QUAL-W2 model, developed by Portland State University, simulates water quality and flow. Recommendations to expand on this model and have it include sediment transport are implemented in this report. Existing one-, two-, and three-dimensional models are reviewed and assessed for their sediment transport methodology. A laterally (width) averaged sediment concentration model is developed as an Upwind Center Space Scheme using CE-QUAL-W2 data. The scheme includes a method to calculate scour for sediment concentration and results of the model are shown for a simulated branch of the Spokane River. Close

• 3. [Article] Estimation of Historic Flows and Sediment Loads to San Francisco Bay, 1849 – 2011

  River flow and sediment transport in estuaries influence morphological development over decadal and century time scales, but hydrological and sedimentological records are typically too short to adequately ...

  Citation × Citation Citation Abstract Copy Title: Estimation of Historic Flows and Sediment Loads to San Francisco Bay, 1849 – 2011 Author: Moftakhari Rostamkhani, Hamed, Jay, David A., Talke, Stefan A., Schoellhamer, David H. Year: 2015 River flow and sediment transport in estuaries influence morphological development over decadal and century time scales, but hydrological and sedimentological records are typically too short to adequately characterize long-term trends. In this study, we recover archival records and apply a rating curve approach to develop the first instrumental estimates of daily delta inflow and sediment loads to San Francisco Bay (1849 – 1929). The total sediment load is constrained using sedimentation/erosion estimated from bathymetric survey data to produce continuous daily sediment transport estimates from 1849 to 1955, the time period prior to sediment load measurements. We estimate that ~55% (45 – 75%) of the ~1500±400 million tons (Mt) of sediment delivered to the estuary between 1849 and 2011 was the result of anthropogenic alteration in the watershed that increased sediment supply. Also, the seasonal timing of sediment flux events has shifted because significant spring-melt floods have decreased, causing estimated springtime transport (April 1st to June 30th) to decrease from ~25% to ~15% of the annual total. By contrast, wintertime sediment loads (December 1st to March 31st) have increased from ~70% to ~80%. A ~35% reduction of annual flow since the 19th century along with decreased sediment supply has resulted in a ~50% reduction in annual sediment delivery. The methods developed in this study can be applied to other systems for which unanalyzed historic data exist. Title: Estimation of Historic Flows and Sediment Loads to San Francisco Bay, 1849 – 2011 Author: Moftakhari Rostamkhani, Hamed, Jay, David A., Talke, Stefan A., Schoellhamer, David H. Year: 2015 River flow and sediment transport in estuaries influence morphological development over decadal and century time scales, but hydrological and sedimentological records are typically too short to adequately characterize long-term trends. In this study, we recover archival records and apply a rating curve approach to develop the first instrumental estimates of daily delta inflow and sediment loads to San Francisco Bay (1849 – 1929). The total sediment load is constrained using sedimentation/erosion estimated from bathymetric survey data to produce continuous daily sediment transport estimates from 1849 to 1955, the time period prior to sediment load measurements. We estimate that ~55% (45 – 75%) of the ~1500±400 million tons (Mt) of sediment delivered to the estuary between 1849 and 2011 was the result of anthropogenic alteration in the watershed that increased sediment supply. Also, the seasonal timing of sediment flux events has shifted because significant spring-melt floods have decreased, causing estimated springtime transport (April 1st to June 30th) to decrease from ~25% to ~15% of the annual total. By contrast, wintertime sediment loads (December 1st to March 31st) have increased from ~70% to ~80%. A ~35% reduction of annual flow since the 19th century along with decreased sediment supply has resulted in a ~50% reduction in annual sediment delivery. The methods developed in this study can be applied to other systems for which unanalyzed historic data exist. Close

• 4. [Article] The applicability of microcomputers to local water management

  Historically, hydrologic models have been available only on mainframe computers and have therefore not been used by local water managers to support daily decisions. The development of the microcomputer ...

  Citation × Citation Citation Abstract Copy Title: The applicability of microcomputers to local water management Author: Allen, Roderick Lee Year: 1985 Historically, hydrologic models have been available only on mainframe computers and have therefore not been used by local water managers to support daily decisions. The development of the microcomputer presents an opportunity for that to change. Mathematical models of soil moisture and river routing are selected, developed and tested for use on a microcomputer as an aid to local water management. The models are then integrated with an appropriate data base in a computer program written for a microcomputer. The result is a Decision Support System for local water managers. In order to evaluate the feasibility of using the Decision Support System, an application of the program to a small hypothetical river and irrigation system is carried out. The speed of execution indicates that the use of the Decision Support System on this class of computer under the present configuration may be possible if software or hardware changes can reduce data transfer times to and from disk. Title: The applicability of microcomputers to local water management Author: Allen, Roderick Lee Year: 1985 Historically, hydrologic models have been available only on mainframe computers and have therefore not been used by local water managers to support daily decisions. The development of the microcomputer presents an opportunity for that to change. Mathematical models of soil moisture and river routing are selected, developed and tested for use on a microcomputer as an aid to local water management. The models are then integrated with an appropriate data base in a computer program written for a microcomputer. The result is a Decision Support System for local water managers. In order to evaluate the feasibility of using the Decision Support System, an application of the program to a small hypothetical river and irrigation system is carried out. The speed of execution indicates that the use of the Decision Support System on this class of computer under the present configuration may be possible if software or hardware changes can reduce data transfer times to and from disk. Close

• 5. [Article] Estimating River Discharge Using Multiple-Tide Gauges Distributed Along a Channel

  Reliable estimation of freshwater inflow to the ocean from large tidal rivers is vital for water resources management and climate analyses. Discharge gauging stations are typically located beyond the tidal ...

  Citation × Citation Citation Abstract Copy Title: Estimating River Discharge Using Multiple-Tide Gauges Distributed Along a Channel Author: Moftakhari, Hamed R., Jay, David A, Talke, Stefan Year: 2016 Reliable estimation of freshwater inflow to the ocean from large tidal rivers is vital for water resources management and climate analyses. Discharge gauging stations are typically located beyond the tidal intrusion reach, such that inputs and losses occurring closer to the ocean are not included. Here, we develop a method of estimating river discharge using multiple gauges and time-dependent tidal statistics determined via wavelet analysis. The Multiple-gauge Tidal Discharge Estimate (MTDE) method is developed using data from the Columbia River and Fraser River estuaries and calibrated against river discharge. Next, we evaluate the general applicability of MTDE by testing an idealized two-dimensional numerical model, with a convergent cross-sectional profile, for eighty-one cases in which nondimensional numbers for friction, river flow, and convergence length scale are varied. The simulations suggest that MTDE is applicable to a variety of tidal systems. Model results and data analyses together suggest that MTDE works best with at least three gauges: a reference station near the river mouth, and two upstream gauges that respond strongly to distinct portions of the observed range of flow. The balance between tidal damping and amplifying factors determines the favorable location of the gauges. Compared to previous studies, the MTDE method improves the time resolution of estimates (from 2.5 to < 1 week) and is applicable to systems with mixed diurnal/semidiurnal tides. However, model results suggest that tide-induced residual flows such as the Stokes drift may still affect the accuracy of MTDE at seaward locations during periods of low river discharge. Title: Estimating River Discharge Using Multiple-Tide Gauges Distributed Along a Channel Author: Moftakhari, Hamed R., Jay, David A, Talke, Stefan Year: 2016 Reliable estimation of freshwater inflow to the ocean from large tidal rivers is vital for water resources management and climate analyses. Discharge gauging stations are typically located beyond the tidal intrusion reach, such that inputs and losses occurring closer to the ocean are not included. Here, we develop a method of estimating river discharge using multiple gauges and time-dependent tidal statistics determined via wavelet analysis. The Multiple-gauge Tidal Discharge Estimate (MTDE) method is developed using data from the Columbia River and Fraser River estuaries and calibrated against river discharge. Next, we evaluate the general applicability of MTDE by testing an idealized two-dimensional numerical model, with a convergent cross-sectional profile, for eighty-one cases in which nondimensional numbers for friction, river flow, and convergence length scale are varied. The simulations suggest that MTDE is applicable to a variety of tidal systems. Model results and data analyses together suggest that MTDE works best with at least three gauges: a reference station near the river mouth, and two upstream gauges that respond strongly to distinct portions of the observed range of flow. The balance between tidal damping and amplifying factors determines the favorable location of the gauges. Compared to previous studies, the MTDE method improves the time resolution of estimates (from 2.5 to < 1 week) and is applicable to systems with mixed diurnal/semidiurnal tides. However, model results suggest that tide-induced residual flows such as the Stokes drift may still affect the accuracy of MTDE at seaward locations during periods of low river discharge. Close

• 6. [Article] Recent Progress in Performance Evaluations and Near Real-Time Assessment of Operational Ocean Products

  Operational ocean forecast systems provide routine marine products to an ever-widening community of users and stakeholders. The majority of users need information about the quality and reliability of the ...

  Citation × Citation Citation Abstract Copy Title: Recent Progress in Performance Evaluations and Near Real-Time Assessment of Operational Ocean Products Author: Hernandez, Fabrice, Blockley, Edward, Brassington, Gary B., Davidson, Fraser, Divakaran, Prasanth, Drévillon, Marie, Ishizaki, Shiro, Garcia-Sotillo, Marcos, Hogan, Patrick J., Lagemaa, Priidik, Levier, Bruno, Martin, Matthew, Mehra, Avichal, Mooers, Christopher, Ferry, Nicolas, Ryan, Andrew, Regnier, Charly, Sellar, Alistair, Smith, Gregory C., Sofianos, Sarantis, Spindler, Todd, Volpe, Gianluca, Wilkin, John, Zaron, Edward, Zhang, Aijun Year: 2015 Operational ocean forecast systems provide routine marine products to an ever-widening community of users and stakeholders. The majority of users need information about the quality and reliability of the products to exploit them fully. Hence, forecast centres have been developing improved methods for evaluating and communicating the quality of their products. Global Ocean Data Assimilation Experiment (GODAE) OceanView, along with the Copernicus European Marine Core Service and other national and international programmes, has facilitated the development of coordinated validation activities among these centres. New metrics, assessing a wider range of ocean parameters, have been defined and implemented in real-time. An overview of recent progress and emerging international standards is presented here. Title: Recent Progress in Performance Evaluations and Near Real-Time Assessment of Operational Ocean Products Author: Hernandez, Fabrice, Blockley, Edward, Brassington, Gary B., Davidson, Fraser, Divakaran, Prasanth, Drévillon, Marie, Ishizaki, Shiro, Garcia-Sotillo, Marcos, Hogan, Patrick J., Lagemaa, Priidik, Levier, Bruno, Martin, Matthew, Mehra, Avichal, Mooers, Christopher, Ferry, Nicolas, Ryan, Andrew, Regnier, Charly, Sellar, Alistair, Smith, Gregory C., Sofianos, Sarantis, Spindler, Todd, Volpe, Gianluca, Wilkin, John, Zaron, Edward, Zhang, Aijun Year: 2015 Operational ocean forecast systems provide routine marine products to an ever-widening community of users and stakeholders. The majority of users need information about the quality and reliability of the products to exploit them fully. Hence, forecast centres have been developing improved methods for evaluating and communicating the quality of their products. Global Ocean Data Assimilation Experiment (GODAE) OceanView, along with the Copernicus European Marine Core Service and other national and international programmes, has facilitated the development of coordinated validation activities among these centres. New metrics, assessing a wider range of ocean parameters, have been defined and implemented in real-time. An overview of recent progress and emerging international standards is presented here. Close

• 7. [Article] Predictive Time Series Analysis Linking Bengal Cholera with Terrestrial Water Storage Measured from Gravity Recovery and Climate Experiment Sensors

  Outbreaks of diarrheal diseases, including cholera, are related to floods and droughts in regions where water and sanitation infrastructure are inadequate or insufficient. However, availability of data ...

  Citation × Citation Citation Abstract Copy Title: Predictive Time Series Analysis Linking Bengal Cholera with Terrestrial Water Storage Measured from Gravity Recovery and Climate Experiment Sensors Author: Jutla, Antarpreet, Akanda, Ali, Unnikrishnan, Avinash, Huq, Anwar, Colwell, Rita Year: 2015 Outbreaks of diarrheal diseases, including cholera, are related to floods and droughts in regions where water and sanitation infrastructure are inadequate or insufficient. However, availability of data on water scarcity and abundance in transnational basins, are a prerequisite for developing cholera forecasting systems. With more than a decade of terrestrial water storage (TWS) data from the Gravity Recovery and Climate Experiment, conditions favorable for predicting cholera occurrence may now be determined. We explored lead–lag relationships between TWS in the Ganges–Brahmaputra–Meghna basin and endemic cholera in Bangladesh. Since bimodal seasonal peaks in cholera in Bangladesh occur during spring and autumn seasons, two separate logistical models between TWS and disease time series (2002–2010) were developed. TWS representing water availability showed an asymmetrical, strong association with cholera prevalence in the spring (τ = −0.53; P < 0.001) and autumn (τ = 0.45; P < 0.001) up to 6 months in advance. One unit (centimeter of water) decrease in water availability in the basin increased odds of above normal cholera by 24% (confidence interval [CI] = 20–31%; P < 0.05) in the spring, while an increase in regional water by 1 unit, through floods, increased odds of above average cholera in the autumn by 29% (CI = 22–33%; P < 0.05). Title: Predictive Time Series Analysis Linking Bengal Cholera with Terrestrial Water Storage Measured from Gravity Recovery and Climate Experiment Sensors Author: Jutla, Antarpreet, Akanda, Ali, Unnikrishnan, Avinash, Huq, Anwar, Colwell, Rita Year: 2015 Outbreaks of diarrheal diseases, including cholera, are related to floods and droughts in regions where water and sanitation infrastructure are inadequate or insufficient. However, availability of data on water scarcity and abundance in transnational basins, are a prerequisite for developing cholera forecasting systems. With more than a decade of terrestrial water storage (TWS) data from the Gravity Recovery and Climate Experiment, conditions favorable for predicting cholera occurrence may now be determined. We explored lead–lag relationships between TWS in the Ganges–Brahmaputra–Meghna basin and endemic cholera in Bangladesh. Since bimodal seasonal peaks in cholera in Bangladesh occur during spring and autumn seasons, two separate logistical models between TWS and disease time series (2002–2010) were developed. TWS representing water availability showed an asymmetrical, strong association with cholera prevalence in the spring (τ = −0.53; P < 0.001) and autumn (τ = 0.45; P < 0.001) up to 6 months in advance. One unit (centimeter of water) decrease in water availability in the basin increased odds of above normal cholera by 24% (confidence interval [CI] = 20–31%; P < 0.05) in the spring, while an increase in regional water by 1 unit, through floods, increased odds of above average cholera in the autumn by 29% (CI = 22–33%; P < 0.05). Close

• 8. [Article] Ensemble Combination of Seasonal Streamflow Forecasts

  Various hydrologic models with different complexities have been developed to represent the characteristics of river basins, improve streamflow forecasts such as seasonal volumetric flow predictions, and ...

  Citation × Citation Citation Abstract Copy Title: Ensemble Combination of Seasonal Streamflow Forecasts Author: Najafi, Mohammad Reza, Moradkhani, Hamid Year: 2015 Various hydrologic models with different complexities have been developed to represent the characteristics of river basins, improve streamflow forecasts such as seasonal volumetric flow predictions, and meet other demands from different stakeholders. Because no single hydrologic model is able to perfectly simulate the observed flow, multimodel combination techniques are developed to combine forecasts obtained from different models and to quantify the uncertainties with the goal of improving upon single-model performance. In this study, a comprehensive set of multimodel ensemble averaging techniques with varying complexities are investigated for operational forecasting over four river basins in the Western United States. Ensemble merging models are divided into three categories of simple, intermediate, and complex, and comparison is made between each class by using a bootstrap approach. Analysis suggests that model combination effectively improves most of the individual seasonal forecasts and can outperform the best forecast model. Simple average, median, Bates-Granger, constrained linear regression, and Bayesian model averaging optimized by expectation maximization showed better results compared with other methods over three basins. For the Rogue River basin, the intermediate and complex models outperformed most of the individual forecasts and the simple methods. Multimodeling techniques based on information criteria showed similar performances. Title: Ensemble Combination of Seasonal Streamflow Forecasts Author: Najafi, Mohammad Reza, Moradkhani, Hamid Year: 2015 Various hydrologic models with different complexities have been developed to represent the characteristics of river basins, improve streamflow forecasts such as seasonal volumetric flow predictions, and meet other demands from different stakeholders. Because no single hydrologic model is able to perfectly simulate the observed flow, multimodel combination techniques are developed to combine forecasts obtained from different models and to quantify the uncertainties with the goal of improving upon single-model performance. In this study, a comprehensive set of multimodel ensemble averaging techniques with varying complexities are investigated for operational forecasting over four river basins in the Western United States. Ensemble merging models are divided into three categories of simple, intermediate, and complex, and comparison is made between each class by using a bootstrap approach. Analysis suggests that model combination effectively improves most of the individual seasonal forecasts and can outperform the best forecast model. Simple average, median, Bates-Granger, constrained linear regression, and Bayesian model averaging optimized by expectation maximization showed better results compared with other methods over three basins. For the Rogue River basin, the intermediate and complex models outperformed most of the individual forecasts and the simple methods. Multimodeling techniques based on information criteria showed similar performances. Close

• 9. [Article] Small Scale Water Filtration Project

  Access to clean drinking water is a large problem that our world is facing today. Consuming contaminated water can lead to the spread of water-borne illnesses. Populations without the security of water ...

  Citation × Citation Citation Abstract Copy Title: Small Scale Water Filtration Project Author: Yang, Elaine, Ming, Lang, Tees, Alex, Galle, Lauren, Coffey, Tristan, Tattersfield, Andria, Brock, Colin Year: 2016 Access to clean drinking water is a large problem that our world is facing today. Consuming contaminated water can lead to the spread of water-borne illnesses. Populations without the security of water struggle to develop, as seen predominately in Africa. As Oregonians prepare for life after a major earthquake which could devastate the infrastructure that delivers clean water to our homes, a water filtration system should be part of a family’s emergency preparedness plan. There are a large variety of processes for achieving fresh water. Combining all of the necessary components to lead to clean water is a complex process, as we have discovered during our field research. We saw an opportunity to create an inexpensive and user friendly device that encompasses all of the required aspects of purifying water for drinking. Title: Small Scale Water Filtration Project Author: Yang, Elaine, Ming, Lang, Tees, Alex, Galle, Lauren, Coffey, Tristan, Tattersfield, Andria, Brock, Colin Year: 2016 Access to clean drinking water is a large problem that our world is facing today. Consuming contaminated water can lead to the spread of water-borne illnesses. Populations without the security of water struggle to develop, as seen predominately in Africa. As Oregonians prepare for life after a major earthquake which could devastate the infrastructure that delivers clean water to our homes, a water filtration system should be part of a family’s emergency preparedness plan. There are a large variety of processes for achieving fresh water. Combining all of the necessary components to lead to clean water is a complex process, as we have discovered during our field research. We saw an opportunity to create an inexpensive and user friendly device that encompasses all of the required aspects of purifying water for drinking. Close

• 10. [Article] The Influence of Channel Deepening on Estuarine Turbidity Levels and Dynamics, as Exemplified by the Ems Estuary

  Active deepening of tidal channels usually results in the alteration of the vertical and the horizontal tide. This may lead to concurrent significant increases in mean suspended matter concentrations (SPM) ...

  Citation × Citation Citation Abstract Copy Title: The Influence of Channel Deepening on Estuarine Turbidity Levels and Dynamics, as Exemplified by the Ems Estuary Author: de Jonge, Victor, Schuttelaars, Henk, van Beusekom, Justus, Talke, Stefan, de Swart, Huib Year: 2014 Active deepening of tidal channels usually results in the alteration of the vertical and the horizontal tide. This may lead to concurrent significant increases in mean suspended matter concentrations (SPM) in coastal plain estuaries, the turbidity maximum (ETM) included. This is exemplified by an extensive analysis of the Ems estuary, a prototypical heavily stressed estuary in the Dutch-German border area. Measurements show that the SPM concentrations in the lower reaches of the estuary have increased an average of 2- to 3-fold between 1954 and 2005, with a 10-fold increase observed in the upper estuary (tidal river). Longitudinal profiles of surface SPM demonstrate that the ETM has moved upstream by up to 25 km and has broadened into a zone 30 km in length which extends into the freshwater tidal river. On an annual scale, variations in freshwater discharge significantly influence the formation and breakdown of the ETM: during low river discharge the ETM approaches equilibrium over 2–3 months, whilst elevated river discharges relocate the ETM downstream over several weeks. An exploratory, semi-analytical model is calibrated to simulate the equilibrium SPM distribution in the upper estuary during five time periods from 1965 to 2005, using archival bathymetric and tidal data. Results suggest that the deepening of tidal channels and a reduction in hydraulic drag have most likely resulted in a landward shift of the SPM trapping location. The measured increase in SPM concentrations and the development of fluid mud around the 1990s likely contributed to reduced mixing and bottom drag, creating a feedback loop that further altered tidal and SPM dynamics. It is argued that the removal of some non-erodible (consolidated) layers in the lower reaches of the estuary has created new internal sediment sources that may be responsible for feeding the observed high SPM concentrations, rather than increased sediment input from the boundaries. All findings are based on and supported by measured short-term seasonal fluctuations, as well as long-term developments of yearly averaged concentrations in the longitudinal SPM distribution. Title: The Influence of Channel Deepening on Estuarine Turbidity Levels and Dynamics, as Exemplified by the Ems Estuary Author: de Jonge, Victor, Schuttelaars, Henk, van Beusekom, Justus, Talke, Stefan, de Swart, Huib Year: 2014 Active deepening of tidal channels usually results in the alteration of the vertical and the horizontal tide. This may lead to concurrent significant increases in mean suspended matter concentrations (SPM) in coastal plain estuaries, the turbidity maximum (ETM) included. This is exemplified by an extensive analysis of the Ems estuary, a prototypical heavily stressed estuary in the Dutch-German border area. Measurements show that the SPM concentrations in the lower reaches of the estuary have increased an average of 2- to 3-fold between 1954 and 2005, with a 10-fold increase observed in the upper estuary (tidal river). Longitudinal profiles of surface SPM demonstrate that the ETM has moved upstream by up to 25 km and has broadened into a zone 30 km in length which extends into the freshwater tidal river. On an annual scale, variations in freshwater discharge significantly influence the formation and breakdown of the ETM: during low river discharge the ETM approaches equilibrium over 2–3 months, whilst elevated river discharges relocate the ETM downstream over several weeks. An exploratory, semi-analytical model is calibrated to simulate the equilibrium SPM distribution in the upper estuary during five time periods from 1965 to 2005, using archival bathymetric and tidal data. Results suggest that the deepening of tidal channels and a reduction in hydraulic drag have most likely resulted in a landward shift of the SPM trapping location. The measured increase in SPM concentrations and the development of fluid mud around the 1990s likely contributed to reduced mixing and bottom drag, creating a feedback loop that further altered tidal and SPM dynamics. It is argued that the removal of some non-erodible (consolidated) layers in the lower reaches of the estuary has created new internal sediment sources that may be responsible for feeding the observed high SPM concentrations, rather than increased sediment input from the boundaries. All findings are based on and supported by measured short-term seasonal fluctuations, as well as long-term developments of yearly averaged concentrations in the longitudinal SPM distribution. Close