Analysis and Study of Flow Patterns and Sediment Deposition in the Forebay of a Forward Intake Pumping Station

In Northwest China, the sediment concentration of the Yellow River is high. A project to investigate the operation of a pumping station shows that the flow patterns in the forebay and inlet tank are disordered, and there is sediment deposition that endangers the normal operation and safety of the pumping station. To solve this problem, the three-dimensional two-phase water-sediment flow in the forebay of the pumping station is modeled by using fluid simulation software, and diagrams of the sediment volume fraction content and vector distribution in the flow layers of different sections are obtained. Combined with the multiphase flow theory of mixtures and the realizable turbulent kinetic energy equation, the location and formation mechanism of each vortex, as well as the area and degree of sediment deposition in the forebay, are analyzed. The actual engineering and numerical simulation results are compared to verify the accuracy of the simulation. The results show that the main reason for sediment deposition is the high sediment concentration of the Yellow River, but the flow pattern disorder is affected by a specific design defect of the forebay, which makes the sediment deposition worse. The results of this study provide specific guidance and methods for the construction and transformation of the forebay of the pump station in the future; construction to weaken the return area to a certain extent can reduce the degree of sedimentation.

Quantifying ecological effects of sedimentation in streams in differing land use management zones

<p>This ecological and geomorphological assessment of Horokiri Stream and Ration Creek was conducted across four longitudinal zones to explore the effects of sediment delivery, run-off, channel form, riparian and in-stream habitat. The Horokiri Stream channel has moved approximately 7 metres westward over the last 20 years, with both banks now covered in long grass, flaxes, natives with a mix of tall canopy trees. Looking at stream, Spearman’s for Ration at Figure 27 (n = 16, rho -0.243, p = 0.36) as deposited sediment increased, MCI decreased, non-significant. Spearman’s for Horokiri at Figure 28 (n = 16, rho 0.247, p = 0.35) as MCI increased with sediment, non-significant. Results from upstream of the riparian zones showed more deposited fine sediment. However, within both the riparian zones the sediment deposition was much lower. The native riparian planting along the stream banks had a positive effect on reducing sedimentation. The findings support the concept that the restoration of riparian zones with buffer widths exceeding 10 metres can improve stream habitat and invertebrate health. There was no relationship between flow and deposition rate P(X2>241.84) = 0.24. Figure 24 shows deposited sediment on MCI depending on land use groups (X2 = 11.81, df = 4, p = 0.019). No statistically significant differences were found (comparing the effect of sediment between different land use management groups). An experiment investigated a disturbance hypothesis in both Ration Creek and Horokiri Stream was conducted during February 2019. The experiment was designed to be long enough to study the effects of four weekly pulse flushing events created by scrapping the stream bed with a drain drag tool and the effects of a press sustained disturbance on the macroinvertebrate community. I measured the sediment and the macroinvertebrate captured in each trap within the experiment site every seven days. My prediction was that macroinvertebrate communities subject to sustained fine sediment delivery (press disturbance) are affected by simulated pulse flushing events (pulse disturbance). A comparison of sediment depositional rate before and after the manipulative experiment (Figure 36) showed higher sediment deposition after the pulse flushing events (1.55 W/A/D) compared to before during the assessment phase (0.88 W/A/D) in Horokiri (t = 2.35, df = 8.95, p = 0.04), but no significant difference before (1.57 W/A/D) or after (1.38 W/A/D) in Ration (t = -0.818, df = 7.71, p = 0.44). It appeared that the smaller riparian buffer width of 2-5m at Ration Creek did not limit sediment deposition. The effects of sediment disturbance in the experiment reflect the rapid ability of macroinvertebrates to respond to sediment by drifting out of unsuitable areas. The weekly pulse disturbance events resulted in increased sediment deposition compared to the background levels of sediment deposition (indicative of a press disturbance) in both streams. As pulse disturbance events increased, the number of macroinvertebrate taxa decreased. Horokiri Stream invertebrate communities declined by 33% compared to Ration Creek which declined by 50%.</p>

Quantifying ecological effects of sedimentation in streams in differing land use management zones

<p>This ecological and geomorphological assessment of Horokiri Stream and Ration Creek was conducted across four longitudinal zones to explore the effects of sediment delivery, run-off, channel form, riparian and in-stream habitat. The Horokiri Stream channel has moved approximately 7 metres westward over the last 20 years, with both banks now covered in long grass, flaxes, natives with a mix of tall canopy trees. Looking at stream, Spearman’s for Ration at Figure 27 (n = 16, rho -0.243, p = 0.36) as deposited sediment increased, MCI decreased, non-significant. Spearman’s for Horokiri at Figure 28 (n = 16, rho 0.247, p = 0.35) as MCI increased with sediment, non-significant. Results from upstream of the riparian zones showed more deposited fine sediment. However, within both the riparian zones the sediment deposition was much lower. The native riparian planting along the stream banks had a positive effect on reducing sedimentation. The findings support the concept that the restoration of riparian zones with buffer widths exceeding 10 metres can improve stream habitat and invertebrate health. There was no relationship between flow and deposition rate P(X2>241.84) = 0.24. Figure 24 shows deposited sediment on MCI depending on land use groups (X2 = 11.81, df = 4, p = 0.019). No statistically significant differences were found (comparing the effect of sediment between different land use management groups). An experiment investigated a disturbance hypothesis in both Ration Creek and Horokiri Stream was conducted during February 2019. The experiment was designed to be long enough to study the effects of four weekly pulse flushing events created by scrapping the stream bed with a drain drag tool and the effects of a press sustained disturbance on the macroinvertebrate community. I measured the sediment and the macroinvertebrate captured in each trap within the experiment site every seven days. My prediction was that macroinvertebrate communities subject to sustained fine sediment delivery (press disturbance) are affected by simulated pulse flushing events (pulse disturbance). A comparison of sediment depositional rate before and after the manipulative experiment (Figure 36) showed higher sediment deposition after the pulse flushing events (1.55 W/A/D) compared to before during the assessment phase (0.88 W/A/D) in Horokiri (t = 2.35, df = 8.95, p = 0.04), but no significant difference before (1.57 W/A/D) or after (1.38 W/A/D) in Ration (t = -0.818, df = 7.71, p = 0.44). It appeared that the smaller riparian buffer width of 2-5m at Ration Creek did not limit sediment deposition. The effects of sediment disturbance in the experiment reflect the rapid ability of macroinvertebrates to respond to sediment by drifting out of unsuitable areas. The weekly pulse disturbance events resulted in increased sediment deposition compared to the background levels of sediment deposition (indicative of a press disturbance) in both streams. As pulse disturbance events increased, the number of macroinvertebrate taxa decreased. Horokiri Stream invertebrate communities declined by 33% compared to Ration Creek which declined by 50%.</p>

Understanding the hydrological and physicochemical drivers of Phormidium proliferation in the Hutt and Waipoua Rivers

<p>The Hutt and Waipoua rivers are affected annually by proliferations of the potentially toxic benthic cyanobacteria - Phormidium. Ingestion of these mats has resulted in numerous dog deaths and is therefore a risk to human health. This has resulted in the establishment of warning signs at many recreational sites on these rivers during summer months. Recent research has concluded that river flow and water column nutrients are two of the primary factors regulating Phormidium growth. Proliferations tend to form in rivers where there is slightly elevated water column dissolved inorganic nitrogen, low dissolved reactive phosphorus, and during periods of stable flow. It has been hypothesised that fine sediment may provide a source of phosphorus for Phormidium. These mats ‘capture’ fine sediment suspended in the water column, which becomes incorporated into the mat matrices when motile Phormidium filaments move over the sediment. Diffusive boundary layers at the surface of the mats limit the flow of nutrients and gases between mat and bulk river water, creating conditions (for example, lower dissolved oxygen, elevated pH) conducive to the release of phosphorus from sediment. The aim of this project was to identify why Phormidium proliferates in certain parts of the Hutt and Waipoua rivers, as well as investigate the relationship between fine sediment and mat growth. Monitoring of river data was carried out in the Hutt and Waipoua Rivers between November 2014 and May 2015. Over this period, physicochemical and hydrological data was monitored to identify the influencing factors of Phormidium abundance. During February 2015, sediment traps were deployed to determine the sedimentation rates in parallel to Phormidium cover at each site. The collected fine sediment was fractionated and analysed for biologically available phosphorus. Finally, a manipulative study using stream channel mesocosms was undertaken to provide causative evidence that fine sediment deposition influences Phormidium growth. In this three-week study, four mesocosms were deployed containing different fine sediment treatments. Biomass samples were collected at regular intervals to determine total photosynthetic biomass and Phormidium specifically. Phormidium cover during 2014-15 was influenced by water column nitrate-nitrite nitrogen concentrations and sediment deposition. Phormidium cover was considerably lower compared to previous years, with a maximum cover of 20.7% occurring in the Hutt River during February 2015. Analysis of historical flow and nutrient data suggests that the annual variation in Phormidium proliferation over the summer months was site specific and not generally driven by flow or nutrient concentrations. It is likely that fine sediment plays a role in providing Phormidium mats with phosphorus in the Hutt and Waipoua River. This is shown through phosphorus concentrations within Phormidium mat water, which were 200-fold higher than the bulk water column. Maximum values of sedimentation, 272.0 g/m²/day, and biologically available phosphorus (bound to sediment) 1.4 mg P g⁻¹, occurred at sites with the highest Phormidium cover, which further confirms this correlation. Furthermore, mesocosm experiments showed that Phormidium biomass increased significantly (p=0.015) with an increased amount of sediment. However, the maximum biomass of 64.75 mg/m² did not occur in the mesocosm channel with the most sediment added to it. This suggests that a deposition threshold exists due to the attenuation of light. Findings from this research provide some insights in to management options which may help to mitigate Phormidium proliferations in the future. The data indicates that reducing sediment inputs, or resuspension of fine sediment during flood remediation works, would reduce Phormidium proliferations. Riparian planting as well as the collaboration with local councils is needed to help reduce diffuse and remaining point sources of sediment and river bed disturbance during flood protection activities. Using a combination of observational and experimental studies, this research has shown that multiple factors influence Phormidium proliferation, and has highlighted the key role that fine sediment plays. Suggestions for future studies include in-river experiments to further explore the role of fine sediment and the optimisation of mesocosms, which may also help to investigate finer scale data on causative factors such as sediment thresholds.</p>

Understanding the hydrological and physicochemical drivers of Phormidium proliferation in the Hutt and Waipoua Rivers

<p>The Hutt and Waipoua rivers are affected annually by proliferations of the potentially toxic benthic cyanobacteria - Phormidium. Ingestion of these mats has resulted in numerous dog deaths and is therefore a risk to human health. This has resulted in the establishment of warning signs at many recreational sites on these rivers during summer months. Recent research has concluded that river flow and water column nutrients are two of the primary factors regulating Phormidium growth. Proliferations tend to form in rivers where there is slightly elevated water column dissolved inorganic nitrogen, low dissolved reactive phosphorus, and during periods of stable flow. It has been hypothesised that fine sediment may provide a source of phosphorus for Phormidium. These mats ‘capture’ fine sediment suspended in the water column, which becomes incorporated into the mat matrices when motile Phormidium filaments move over the sediment. Diffusive boundary layers at the surface of the mats limit the flow of nutrients and gases between mat and bulk river water, creating conditions (for example, lower dissolved oxygen, elevated pH) conducive to the release of phosphorus from sediment. The aim of this project was to identify why Phormidium proliferates in certain parts of the Hutt and Waipoua rivers, as well as investigate the relationship between fine sediment and mat growth. Monitoring of river data was carried out in the Hutt and Waipoua Rivers between November 2014 and May 2015. Over this period, physicochemical and hydrological data was monitored to identify the influencing factors of Phormidium abundance. During February 2015, sediment traps were deployed to determine the sedimentation rates in parallel to Phormidium cover at each site. The collected fine sediment was fractionated and analysed for biologically available phosphorus. Finally, a manipulative study using stream channel mesocosms was undertaken to provide causative evidence that fine sediment deposition influences Phormidium growth. In this three-week study, four mesocosms were deployed containing different fine sediment treatments. Biomass samples were collected at regular intervals to determine total photosynthetic biomass and Phormidium specifically. Phormidium cover during 2014-15 was influenced by water column nitrate-nitrite nitrogen concentrations and sediment deposition. Phormidium cover was considerably lower compared to previous years, with a maximum cover of 20.7% occurring in the Hutt River during February 2015. Analysis of historical flow and nutrient data suggests that the annual variation in Phormidium proliferation over the summer months was site specific and not generally driven by flow or nutrient concentrations. It is likely that fine sediment plays a role in providing Phormidium mats with phosphorus in the Hutt and Waipoua River. This is shown through phosphorus concentrations within Phormidium mat water, which were 200-fold higher than the bulk water column. Maximum values of sedimentation, 272.0 g/m²/day, and biologically available phosphorus (bound to sediment) 1.4 mg P g⁻¹, occurred at sites with the highest Phormidium cover, which further confirms this correlation. Furthermore, mesocosm experiments showed that Phormidium biomass increased significantly (p=0.015) with an increased amount of sediment. However, the maximum biomass of 64.75 mg/m² did not occur in the mesocosm channel with the most sediment added to it. This suggests that a deposition threshold exists due to the attenuation of light. Findings from this research provide some insights in to management options which may help to mitigate Phormidium proliferations in the future. The data indicates that reducing sediment inputs, or resuspension of fine sediment during flood remediation works, would reduce Phormidium proliferations. Riparian planting as well as the collaboration with local councils is needed to help reduce diffuse and remaining point sources of sediment and river bed disturbance during flood protection activities. Using a combination of observational and experimental studies, this research has shown that multiple factors influence Phormidium proliferation, and has highlighted the key role that fine sediment plays. Suggestions for future studies include in-river experiments to further explore the role of fine sediment and the optimisation of mesocosms, which may also help to investigate finer scale data on causative factors such as sediment thresholds.</p>

Improvement in the Sediment Management of a Lagoon Harbor: The Case of Marano Lagunare, Italy

Port silting is a common and natural process which often causes serious inconveniences for safe navigation and requires expensive dredging operations to keep the port operative. Sediment deposition is closely related to the exchange water between the basin and the surrounding environment; one way to limit deposits is by reducing the flow entering the port. However, this may be in contrast with the need for adequate sediment quality, which in turn is closely related to an appropriate water current. This seems to be particularly important in lagoon environments, where sediments are often polluted, making its disposal more complicated and costly. The present paper investigates the situation of the port of Marano Lagunare (Italy) by means of a bidimensional morphological-hydrodynamic and spectral coupled model. To reduce the sediment input into the port, the closure of a secondary port entrance is usually suggested. However, this work demonstrates that a complete dredging of the secondary port inlet allows for an increase in water circulation or efficiency renewal, which ensures a better oxygenation at the bottom of the canals.