title: Three-dimensional numerical simulation of mixing patterns at open channel confluences

authors: Aghazadegan, Ali

abstract: Open channel confluences, where two streams or rivers converge, play a crucial role in hydraulic engineering and river dynamics. These confluences are characterized by complex hydrodynamics influenced by the discharge ratios of merging water bodies. This study investigated the mixing structure at open channel confluences using three-dimensional numerical modeling. A comprehensive three-dimensional numerical model was developed and validated against a dataset obtained from controlled laboratory experiments. This dataset incorporated three-dimensional time-averaged velocity measurements. The skew-induced and stress-induced equation systems were adopted as the core governing equations, providing a framework for simulating various scenarios. A total of ten different cases were analyzed. The results highlighted the effect of discharge ratios on turbulence, lateral and vertical vorticities, and the distribution of mixing, which intensified with higher magnitudes of discharge ratios. The mixing structure, driven by velocity gradients and vorticity, revealed the significant role of lateral and vertical vorticities in determining hydrodynamic behaviors and mixing distributions at confluences. Specifically, the momentum ratio of incoming flows governed the spatial evolution of mixing processes. This study revealed that the distribution of mixing served as a key indicator for identifying the formation of mid-channel scours. High normalized velocities induced toward the left bank led to the superelevation of the water surface, enhancing the potential for bed material and the formation of significant scour holes beneath the elevated water surface. This novel approach provides a deeper understanding of the mixing patterns at confluences, particularly in scenarios with equilibrated discharge ratios but in different magnitudes.

text: Three-dimensional numerical simulation of mixing patterns at open channel confluences Open channel confluences, where two streams or rivers converge, play a crucial role in hydraulic engineering and river dynamics. These confluences are characterized by complex hydrodynamics influenced by the discharge ratios of merging water bodies. This study investigated the mixing structure at open channel confluences using three-dimensional numerical modeling. A comprehensive three-dimensional numerical model was developed and validated against a dataset obtained from controlled laboratory experiments. This dataset incorporated three-dimensional time-averaged velocity measurements. The skew-induced and stress-induced equation systems were adopted as the core governing equations, providing a framework for simulating various scenarios. A total of ten different cases were analyzed. The results highlighted the effect of discharge ratios on turbulence, lateral and vertical vorticities, and the distribution of mixing, which intensified with higher magnitudes of discharge ratios. The mixing structure, driven by velocity gradients and vorticity, revealed the significant role of lateral and vertical vorticities in determining hydrodynamic behaviors and mixing distributions at confluences. Specifically, the momentum ratio of incoming flows governed the spatial evolution of mixing processes. This study revealed that the distribution of mixing served as a key indicator for identifying the formation of mid-channel scours. High normalized velocities induced toward the left bank led to the superelevation of the water surface, enhancing the potential for bed material and the formation of significant scour holes beneath the elevated water surface. This novel approach provides a deeper understanding of the mixing patterns at confluences, particularly in scenarios with equilibrated discharge ratios but in different magnitudes.

year: 2025

title: An Integrated Stratigraphy of Tauranga Harbour

authors: MacPherson, David

subjects: Tauranga

abstract: Tauranga Basin is a Quaternary basin filled with successions of terrestrial and coastal sediments. The largest feature of Tauranga Basin is Tauranga Harbour, a 570km2 estuary. This is home to the Port of Tauranga, New Zealands largest export port. Studies conducted following an initial study by Davis and Healy (1993) have found complex distributions of the sediments within the dredged shipping channel. This research used 86 vibracores and limited seismic data to identify four main facies within the shallow subsurface of the dredged channel and establish their distribution.
Four facies were identified within the shallow subsurface: the Volcanic Sand facies, a silt to fine sand volcaniclastic succession; the Silt facies, a silt to very fine sand lacustrine deposit; the Coastal Sands facies, a medium to coarse coastal sand deposit; and the Pumiceous Sand Facies, a medium to coarse sand succession with abundant pumice.

Within the dredged shipping channel, the Volcanic Sands and Silt facies outcrop at the surface, and appear as ridges in the subsurface. Draped over these ridges is the Coastal Sands facies, which in some cores is overlain by Pumiceous Sands. The Volcanic Sands facies represents a succession of tephra deposits, with some reworking between depositional events. In the Maunganui Roads region of the harbour this is overlain by the lacustrine Silt facies, formed from the reworking of the Volcanic Sands. The region was then inundated by the Holocene marine transgression, leading to the deposition of the Coastal Sands facies, sourced from offshore. This Coastal Sands facies is then overlain in areas by Pumiceous Sands, small mobile sand waves that exist within the shipping channel. These are formed following the erosion of ignimbrite cliffs around the harbour, with some input from the outside the harbour. This represents a change in source for sedimentation in the harbour.

An updated model of the paleogeographic development of the harbour is presented, using data from this and other studies. This model shows the presence of a braided river flowing through Stella Passage, before the development of a lake and the subsequent Holocene marine transgression leading to the evolution of the sand spit and Matakana barrier island.

text: An Integrated Stratigraphy of Tauranga Harbour Tauranga Basin is a Quaternary basin filled with successions of terrestrial and coastal sediments. The largest feature of Tauranga Basin is Tauranga Harbour, a 570km2 estuary. This is home to the Port of Tauranga, New Zealands largest export port. Studies conducted following an initial study by Davis and Healy (1993) have found complex distributions of the sediments within the dredged shipping channel. This research used 86 vibracores and limited seismic data to identify four main facies within the shallow subsurface of the dredged channel and establish their distribution.
Four facies were identified within the shallow subsurface: the Volcanic Sand facies, a silt to fine sand volcaniclastic succession; the Silt facies, a silt to very fine sand lacustrine deposit; the Coastal Sands facies, a medium to coarse coastal sand deposit; and the Pumiceous Sand Facies, a medium to coarse sand succession with abundant pumice.

Within the dredged shipping channel, the Volcanic Sands and Silt facies outcrop at the surface, and appear as ridges in the subsurface. Draped over these ridges is the Coastal Sands facies, which in some cores is overlain by Pumiceous Sands. The Volcanic Sands facies represents a succession of tephra deposits, with some reworking between depositional events. In the Maunganui Roads region of the harbour this is overlain by the lacustrine Silt facies, formed from the reworking of the Volcanic Sands. The region was then inundated by the Holocene marine transgression, leading to the deposition of the Coastal Sands facies, sourced from offshore. This Coastal Sands facies is then overlain in areas by Pumiceous Sands, small mobile sand waves that exist within the shipping channel. These are formed following the erosion of ignimbrite cliffs around the harbour, with some input from the outside the harbour. This represents a change in source for sedimentation in the harbour.

An updated model of the paleogeographic development of the harbour is presented, using data from this and other studies. This model shows the presence of a braided river flowing through Stella Passage, before the development of a lake and the subsequent Holocene marine transgression leading to the evolution of the sand spit and Matakana barrier island.

year: 2016

title: Evaluation of iwi and hapū participation in the resource consents processes of six district councils

authors: Backhurst, Michael

subjects: New Zealand

abstract: This working paper analyses the processes adopted by councils for involving hapū/iwi in plan implementation, including the resource consents process. Three topic issues were investigated to assess plan implementation — urban amenity, storm water, and issues of importance to iwi. Questions were asked about the capacity of hapū/iwi to engage in the resource consent process, which resource issues were of concern to them, their relationship with council and consent applicants, and their perception of the consent process. Most resources listed in the questionnaire were of concern to hapū/iwi, with water quality, wāhi tapu and heritage the most commonly cited. In conclusion, we found a general dissatisfaction on the part of hapū/iwi with councils’ performance with respect to both Treaty relationships and consent processing under the RMA. A further contributing factor to the poor relationships found between hapū/iwi and councils, was the lack of clarity over the role of hapū and iwi in resource management. In several districts, diverging responses from hapū/iwi and councils to questions about level of understanding and commitment suggests there is a need for more effective communication. These problems are compounded by the generally low capacity of hapū/iwi to participate in resource consent processes. These findings suggest that there is much to be done to improve relationships and behaviour of these key stakeholder groups in the plan implementation process if key provisions in the RMA related to hapū/iwi interests are to be fulfilled. The differences shown in reciprocal perceptions have serious implications for establishing a sound working partnership between councils and hapū/iwi in their areas. Making clear these discrepancies is a first step towards taking the measures needed for building a better partnership. Further, the capacity of hapū/iwi to participate could be better utilised if there was greater integration between regional and district councils on issues of significance and processes for iwi involvement.

text: Evaluation of iwi and hapū participation in the resource consents processes of six district councils This working paper analyses the processes adopted by councils for involving hapū/iwi in plan implementation, including the resource consents process. Three topic issues were investigated to assess plan implementation — urban amenity, storm water, and issues of importance to iwi. Questions were asked about the capacity of hapū/iwi to engage in the resource consent process, which resource issues were of concern to them, their relationship with council and consent applicants, and their perception of the consent process. Most resources listed in the questionnaire were of concern to hapū/iwi, with water quality, wāhi tapu and heritage the most commonly cited. In conclusion, we found a general dissatisfaction on the part of hapū/iwi with councils’ performance with respect to both Treaty relationships and consent processing under the RMA. A further contributing factor to the poor relationships found between hapū/iwi and councils, was the lack of clarity over the role of hapū and iwi in resource management. In several districts, diverging responses from hapū/iwi and councils to questions about level of understanding and commitment suggests there is a need for more effective communication. These problems are compounded by the generally low capacity of hapū/iwi to participate in resource consent processes. These findings suggest that there is much to be done to improve relationships and behaviour of these key stakeholder groups in the plan implementation process if key provisions in the RMA related to hapū/iwi interests are to be fulfilled. The differences shown in reciprocal perceptions have serious implications for establishing a sound working partnership between councils and hapū/iwi in their areas. Making clear these discrepancies is a first step towards taking the measures needed for building a better partnership. Further, the capacity of hapū/iwi to participate could be better utilised if there was greater integration between regional and district councils on issues of significance and processes for iwi involvement.

year: 2004-03