Spring Tide Conditions Research Articles

Adaptive water management in response to tidal inundation and sea level rise on tidal agricultural lowlands of Katingan, Central Kalimantan

Decreased water management systems and sea level rise cause inundation in the Katingan tidal agricultural lowland. Excessive and prolonged inundation can decrease rice production or even loss of rice land. A study was conducted to provide adaptive water management for controlling water levels in canals and rice crop fields inundation. For this purpose, a combined one- and two-dimensional unsteady flow method was used in HEC-RAS. The scenario of water level control uses sluice and flap gates in secondary canals. Under spring tide conditions, water level control with gates decreases the inundation area by 95.62%. Likewise, in the 25 and 50-year sea level rise scenarios, inundation decreased by 88.51% and 82.25%. In the spring tide condition, the duration of inundation is decreased from 3.5 to 0.9 days. Under 25 and 50-year sea level rise scenarios, the duration of inundation was decreased from 3.7 to 3 days and from 4.3 to 4.1 days. The use of gates significantly decreases inundation in the spring tide condition, but under sea level rise in 25 and 50-year, the depth and duration of inundation are still dangerous for rice crops; therefore, it is necessary to advance water management control for the sustainability of rice fields.

HYDRODYNAMIC ASSESSMENT ALONG THE COAST OF TANJUNG SEDELI, MALAYSIA

Tidal influence plays a significant role in coastal hydrodynamics as the impact may lead to coastal erosion. Tanjung Sedeli located on the southern coast of Malaysia is exposed to low tidal issues which disrupts the navigation of local fishermen due to the shallow river mouth in the area. This study presents the hydrodynamic processes along the shoreline of Tanjung Sedeli. BLUEKENUE was used as the pre-processor to create a bathymetry file and perform mesh generation to set up the initial model boundary which functions as input files for numerical study. TELEMAC2D further processes the hydrodynamic data (tides and currents), calibrated, and validated with the measured field data collected between 24th September to 6th October 2020 covering both spring and neap tide conditions. The nature of tides in the area was mainly mixed tides, predominantly semidiurnal tides. Modelled hydrodynamic values show good conformity with field measurements with an error of 1.4% for water level values, 10.6% and 20o for current speed and direction respectively. Water flows north into the estuary during spring tide with maximum velocity is 0.756m/s surrounding the river mouth and Pulau Tagal. Low velocity values were recorded at the left bank of the river (0.028 m/s) and Pulau Tagal (0.085 m/s) during spring tide. This study provides information on current hydrodynamic condition of the study area.

Investigation of physical properties and suspended particulate matter discharge in a macrotidal estuary at the Amazon-semiarid transition zone

This study evaluated the hydrodynamic circulation and discharge of Suspended Particulate Matter (SPM) in the Arraial-São José Estuarine Complex (ASJEC) located at the Amazon-semiarid interface, northeastern Brazil. Quasi-synoptic data were collected in the rainy and dry seasons of 2017 under spring tide conditions. For each sampling event, two mooring stations (one downstream [S-A] and one upstream [S-B]) were deployed during a complete tidal cycle. The physical characteristics in the rainy and dry seasons enabled dividing the estuarine complex into zones, with a mixing zone/coastal zone interface and a tidal river zone/mixing zone interface. The estuary is vertically quasi-homogeneous, indicating conditions of high vertical instability. The currents at the stations were more intense during the flood tide, demonstrating the importance of the marine component in the region. The estuarine system ranged from partially mixed to well mixed at both stations in the rainy season and was well mixed at both stations in the dry season. Total salt transport was towards the upstream portion of the estuary, suggesting the accumulation of matter in the ASJEC, most likely associated with the entrance of marine waters. The input of coastal water in the ASJEC intensifies the baroclinic pressure gradient, which creates a hydraulic barrier, indicating that SPM discharges from the continental drainage to the estuary and is interrupted from the estuary to the adjacent continental shelf.

Hydrodynamic Characteristics and Sediment Distribution Patterns in Wulan Delta Estuary, Demak, Indonesia

The Wulan Delta, located in Wedung, Demak, was formed due to the sedimentation process of the Wulan and Serang rivers. Sediment transport starts from rivers to the sea; the process carries nutrients and various chemicals derived from agricultural, industrial, or household activities. This study aims to analyze the characteristics of hydrodynamics, suspended sediment, and bottom sediments in the Wulan Delta waters, Demak. Field data were collected in transitional season two (October) 2022. The obtained data were then analyzed in the laboratory at the Faculty of Fisheries and Marine Science. Results showed that the speed of the surface current in the study area ranged from 0 to 0.1 m/s in spring tide conditions with a surface current pattern coming from the direction of Semarang toward Jepara and 0–0.18 m/s in neap tide conditions with a current pattern coming from the direction of Jepara toward Semarang. The Wulan Delta has a sedimentary characteristic dominated by fine silt, which is as much as 82%–98%, with a deposition characteristic dominated by wave energy that causes successful sediment sorting with a sorting index of −2.25 to 2 and strongly asymmetrical to a small size with a skewness curve value of two.

Short-term sedimentation dynamics in mesotidal marshes

One of the key questions about wetlands resilience to sea-level rise is whether sediment supply will be enough to keep them coping with growing inundation levels. To address this question, researchers have put a lot of effort into field data collection and ecogeomorphic modelling, in an attempt to identify the tipping points of marsh survival. This study uses fieldwork data to characterize the sediment fluxes between the tidal flats and salt marshes, in the Ria Formosa lagoon (Portugal). Sediment fluxes were measured from the tidal channel towards the mid-upper marsh, during neap and spring tide conditions. The flow magnitude was measured, and induced transport was determined based on shear velocities. Deposition rates, instantaneous suspended sediment and near-bed velocities were linked through theoretical formulas and used to characterize time-averaged conditions for sediment delivery and deposition to the site. The results showed that suspended sediment concentrations and sediment deposition varied across the transect with no specific relation to elevation. Maximum water depths were recorded in the vegetated tidal flat, and the maximum currents were flood dominated, in the order of 0.20 m/s, in the low marsh due to flow-plant interactions and an increase of turbulence. Deposition rates ranged between 20 to 45 g/m2/hr, after a complete tidal cycle, and were higher in the mid-upper marsh. Hydroperiod was not the main contributor to sediment deposition in the study area. Sediment transport was tidally driven, strongly two-dimension during the cycle, and highly influenced by the vegetation. Measurements of marsh sediment flux obtained in our work are diverse from the ones found in the literature and evidence the importance of considering spatio-temporal variability of vegetated platforms in assessing overall marsh bed level changes.

Modelling morphodynamic responses of a natural embayed beach to Typhoon Lekima encountering different tide types

Recent developments in process-based coastal area models such as XBeach provide new opportunities to predict coastal responses to primary forcing mechanisms such as storm hydrodynamic by using 2DH grids. However, due to the lack of measured data, there are few application scenarios of the models. Therefore, more measurement and research are needed. In this paper, the Typhoon Lekima that hitting Zhejiang Province during neap tide period was selected to simulate morphodynamic responses of the Huangcheng Beach by assuming encountering with different tide types. Cross shore measurements with eight cross-shore profiles (named S1 ~ S8 from north to south) of the Huangcheng Beach pre- and post- the Typhoon Lekima respectively were presented. Then a 2DH storm surge and wave coupled model was established with Delft3D Flow/Wave. The model was well calibrated with measured water levels and wave data and provided hydrodynamic boundary conditions of different typhoon and tide types coupling situations for a refined model. The refined model was built using XBeach and simulated the morphological responses of the Huangcheng beach with well verifications. On basis of the numerical results, bed level changes at the eight profiles were analyzed, and the character of erosion and deposition under different tide conditions were illustrated. The net sand volume changes were got smaller under the spring tide condition rather than middle tide and neap tide conditions. Further study of the distribution of wave induced current at different stages of collision, inundation and ebb shown that the stronger current under spring tide condition would increase the sediment transport rate and reduce the deposition volume at profiles S3 and S6 ~ S8, and the total amount of sediment involved in transportation had increased for the whole beach, leading to the reduction of net erosion volume at profiles S1, S2, S4 and S5.

Real-Time Properties of Hydraulic Jump off a Tidal Bore, Its Generation and Transport Mechanisms: A Case Study of the Kampar River Estuary, Indonesia

Since the hydraulic jump off a tidal bore in the Kampar Estuary has never been well-described, real-time measurements of hydraulic jump properties are crucial to understanding the tidal bore characteristics. This study aims to determine the real-time properties of a tidal bore generation, hydraulic jump, and transport mechanism in the Kampar River estuary. Tidal harmonic and range are analyzed using least-square-based tidal modeling. The tidal bore height and turbulent velocity records based on ADCP surveys in the estuary and upstream area are used to determine the hydraulic jump properties. Furthermore, an acoustic-based approach is also employed to quantify the suspended sediment concentration and flux during the passage of the bore. Kampar Estuary is predominated by semidiurnal co-tidal components (M2 and S2), where, based on the phase lag magnitude, it is categorized as an ebb-dominant estuary. This finding is proven by the more intense and prolonged ebb phases, especially during spring tidal conditions where the tidal range reaches 4 m. Of particular concern, the tidal bore height declines by 1.5 m every 20 km upstream with an erratic turbulent velocity. A sudden increase in transverse and vertical velocity during the passage of bore (ranging from −0.9 to 0.2 m/s) reflects the potency of sediment resuspension in the surrounding river edge marked by the significant increase in suspended sediment flux of about 3.7 times larger than at the end of the ebb tide. However, long-term measurement and regular bathymetry surveys are crucial to monitor the tidal bore behavior and morpho-dynamics in the Kampar River estuary.

Observations of Suspended Particulate Matter Concentrations and Particle Size Distributions within a Macrotidal Estuary (Port Curtis Estuary, Australia)

An understanding of suspended particulate matter (SPM) dynamics is of great importance to design awareness and management strategies of estuaries. Using a Laser In Situ Scattering and Transmissiometry (LISST) instrument, variations in suspended particle size volumetric concentrations (VC) and particle size distributions (PSD) were measured at six sites within Port Curtis estuary (Australia). The port is a macrotidal estuary with significant economic and environmental importance. Observed VC and SPM sizes demonstrated spatial and temporal trends strongly controlled by the variable energy conditions operating on the neap and spring cycle timescale, with a clear trend towards increasing concentrations and decreasing SPM sizes with increasing tidal ranges. Mid-estuary sites were characterized by the greatest depth-averaged VC under transitional and spring conditions. Estuary-wide mean spring tide total water profile concentrations revealed a near 300% increase in comparison to neap tide condition concentrations. In the upper-estuary sites the mean contribution of the combined 2.5–35 µm size classes to the total profile PSDs was greatest during all tidal conditions, whilst within the lower-estuary site the combined 35–130 µm size classes were greatest. Mean contributions of the largest size class (300–500 µm) dominated surface-waters throughout the estuary during the neap tide period, which when compared with the transitional and spring tide conditions, demonstrated changes of −82% to −48% and −82% to −40%, respectively. Overall, the results from this case study provides further evidence of the important influence of neap and spring tidal regimes on SPM dynamics within estuarine settings and the need to observe parameter dynamics on such timescales.

Tidal variability of water quality parameters in a mesotidal estuary (Sado Estuary, Portugal)

To establish effective water quality monitoring strategies in estuaries, it is imperative to identify and understand the main drivers for the variation of water quality parameters. The tidal effect is an important factor of the daily and fortnightly variability in several estuaries. However, the extent of that influence on the different physicochemical and biological parameters is still overlooked in some estuarine systems, such as the Sado Estuary, a mesotidal estuary located on the west coast of Portugal. The main objective of this study was to determine how the water quality parameters of the Sado Estuary varied with the fortnightly and the semidiurnal tidal variation. To achieve this goal, sampling campaigns were conducted in May/18, Nov/18 and Jun/19, under neap and spring tidal conditions, with data collection over the tidal cycle. Results were observed to be significantly influenced by the tidal variation, in a large area of the estuary. Flood seemed to mitigate possible effects of nutrient enrichment in the water column. Additionally, significant differences were also observed when considering the different sampling stations. Temperature, Suspended Particulate Matter (SPM) and nutrients showed the highest values at low water. Lastly, the implications of the tidal variability in the evaluation of the water quality according to Water Framework Directive were also discussed, highlighting the importance of studying short-time scale variations and the worst-case scenario to ensure water quality is maintained. These findings are relevant for the implementation of regional management plans and to promote sustainable development.

Hydrodynamical model during east season at Gosong Coastal West Borneo as candidate location of nuclear power plant in Indonesia

Indonesia planned to build the first nuclear power plant in Gosong Coast, Bengkayang Regency, West Kalimantan. This research examined the hydrodynamical conditions in the ocean of Gosong Coast during the eastern season. This hydrodynamic model can be considered in estimating the distribution of various radionuclide wastes that release to the ocean. It was simulated using the Delft3D flow module application for 15 days which included the neap and spring tide conditions. Base on the result of the hydrodynamical model, Gosong Coast had a mixed semidiurnal type of tide with low amplitude. The wind parameters involved higher impacts to the hydrodynamical conditions. The model result did not find significant differences between neap and spring tide periods. There was a flow collision between 2 opposite water currents which was occurred at Burung Archipelagic during flood tide and at the Coastal area of Singkawang City during ebb tide. Therefore, the ocean currents at Gosong Coast flowed directly offshore through Burung Archipelagic during ebb tide. Meanwhile during flood tide, these ocean currents moved to Singkawang and Sambas Coastal area before they deflected toward offshore.

Stratification on the Vertical Structure of the Tidal Ellipse and Power Density Estimation in the Larantuka Strait, East Flores Based on ADCP Measurement Data

An understanding of tidal current stratification with a tidal ellipse in coastal oceanography is needed, especially in the development of power density for renewable energy. The movement of the water mass can be converted into power density, by optimizing potential energy (sea level) and kinetic energy (tidal currents). Interaction between tidal current and stratification layer has been of importance to optimize the energy conversion (also turbine selection) at each depth layer. The stratification on the vertical structure can be described by variability of the tidal ellipse, in terms of the semi-major axis, the semi-minor axis, the direction of rotation, ellipticity, inclination angle and phase. ADCP measurement is implemented at Larantuka Strait to examine the tidal behavior on a vertical layer of depth. M2 tidal constituent presents the highest amplitudes among the tidal constituents, predominantly straight line, being the most energetic in Larantuka Strait. M2 constituent the highest major-axis at the near-surface layer when compared with S2 with 243.7 cm/s, 128.9cm/s respectively. Most ellipses rotate clockwise 74° as inclination characterizes the current ellipse orientation. Estimation power density conversion is shown >20.000 kW/m2, with power density average 5014.9 Watt/m2 in spring tide condition. Power density degenerates at the near-surface layer following changes in the depth layer, major-minor axis, inclination angle, and tidal phase of the tidal ellipse.

Modelling the distribution of microplastics released by wastewater treatment plants in Ria de Vigo (NW Iberian Peninsula)

The accumulation of plastic waste in estuaries is growing due to the increase in their use in daily life and their inadequate treatment on wastewater plants (WWTPs). Hydrodynamic and particle-tracking models were validated and used to improve the knowledge about the distribution and concentration of microplastics released by WWTPs in the Ria de Vigo. Results showed that the Vigo WWTP is the main driver of microplastics to the Ria de Vigo. Besides, 21% of the released microplastics reach the adjacent ocean, 24% remain anchored around the Cies Islands, and a negligible percentage reaches the upper estuary when the emission occurs under ebb on spring tide conditions. A negligible number of released microplastics is exported to the nearby ocean when the emission occurs under neap tide conditions. This research can provide a useful tool to support the identification of monitoring processes and debris removal.

Circulation and suspended sediment transport in a sediment starving ria: the Itapessoca

Abstract The Itapessoca estuary is part of the Itamaraca-Itapessoca Estuarine System, a ria-type estuary located on the northeast Brazilian shore, in the state of Pernambuco. Here we present an assessment of the estuarine circulation, suspended sediment dynamics, and its main transport mechanisms. We carried out a field survey where water level, currents, salinity, temperature, and suspended sediment concentration (SSC) were recorded at 10-minute intervals during two complete semi-diurnal tidal cycles under spring tide conditions. The field survey was conducted in September (2012), which is a transitional period between wet and dry seasons. The water level displayed symmetrical ebb-flood phases; however, currents were ebb-dominated. The freshwater contribution was negligible, and the mean salinity was ~35 g/kg, which is slightly lower than the adjacent shelf values (36.5 g/kg). The SSC transport was driven by the ebb-dominated tidal currents, with the highest values of ~30 mg/l occurring during the peak current during the ebb. The source of the suspended sediment was the erosion from the bottom, and the concentration was much lower than other similar estuaries (e.g., Caravelas). This observation suggests this system is a ‘sediment starved system’ in the sense that it presents a low concentration of suspended sediment.

The role of tides, river discharge and wind on the residual circulation of Maputo Bay

Lateral variability of residual flow was investigated in Maputo Bay in Mozambique, Africa. The bay is nearly rectangular with 30×30 km, mean depth of 5 m. The bay mouth is ∼18 km wide with mean and maximum depth ∼10 m and 30 m, respectively. Tides ranges between 1 and 3 m at neap and spring tides, respectively. The mean annual river flow is ∼225 m3/s, ranging from ∼150 to ∼400 m3/s during winter and summer, respectively. Southeasterly (SE) wind are the most frequent wind during the year followed by northeasterly (NE) winds. In order to scale the relative importance of tides, wind and buoyancy effects on the residual exchange flows, we designed three-dimensional numerical experiments (Delft3D). Results show strong changes among the scenarios and between neap and spring tide conditions. During spring tide, flows becomes more vertically homogeneous and laterally sheared, modulated by the cross-section shape. Most important exchange flows were during neap tides mainly with scenarios forced by tides. There are some locations prone to entrap sediments, such as the inlet of the Incomati river and to the north of Inhaca Isle.

Numerical Modeling of Currents Circulation in Balikpapan Bay during Oil Spill Event on March 31, 2018

The coastal area in Balikpapan Bay and its surrounding area has been devastated after the burst of an underwater oil pipe at the bay on March 31st, 2018, and the crude oil still continues spreading for a few days later. A three-dimensional hydrodynamic model is used to simulate the currents dynamic and investigate the influence of the current circulation on the spreading of the oil spill in Balikpapan Bay from March 31th to April 15th, 2018, to cover the event i.e. several weeks after the oil spill incident. Model results are validated by calculating the RMSE, MAPE and model skill using water level between available observation data at Semayang Port, Balikpapan station and numerical model from October 1st, 2012 to January 1st, 2013. Verification result of tidal elevation data from observation and model prediction shows a good agreement with RMSE = 7.8 cm, MAPE = 14.3% and model skill = 0.995. Surface currents circulation in Balikpapan Bay can be distinguished by the currents pattern on the spring tide and neap tide condition. During the spring tide condition, the surface currents mostly move to the east after coming out from the bay. However, the surface currents are strongly going southward after come out from the bay on the neap tide condition. Based on the satellite images captured for the next days after the event, the spreading pattern of the oil spill seems to be matched to the pattern of surface currents circulation on the spring tide condition. From the analysis of the model result, it shows that the currents circulation playing the main role to disperse the oil spill in Balikpapan Bay towards the Makassar Strait.

Overtopping events on seawall-backed beaches: Santos Bay, SP, Brazil

The overtopping of coastal structures occurs when the free surface of the ocean (total water level – TWL) reaches a maximum elevation that exceeds the crest height of the structures that front the beach. Extreme events increase the TWL due to the combination of astronomical tides, storm surges and wave run-up. In urbanized beaches, such as Santos and Itararé (Santos Bay, São Paulo, Brazil), it is common practice to remove natural protection for the construction of urban infrastructure. This process results in a more vulnerable coastal area that is subjected to overtopping and inundation, leaving low-lying areas at risk. Santos Bay is open to the south, exposing the coastline to the action of more energetic waves associated with cold fronts. In this study, we aim to estimate the most likely scenarios of TWL that result in overtopping at Santos Bay beaches and analyze overtopping events during 2016. The results show that the wider and flatter profiles in the western portion of Santos and in Itararé allow greater protection against storm events and that the steeper eastern stretch of Santos Beach is more exposed to overtopping events. The wave run-up proved to be an important contributor to the TWL. Spring tide conditions also considerably increase the possibility of overtopping in all profiles. The threshold values of the combined wave and sea level are defined to provide predictive estimates of the overtopping and coastal inundation processes.

Modelling Study of Transport Time Scales for a Hyper-Tidal Estuary

This paper presents a study of two transport timescales (TTS), i.e., the residence time and exposure time, of a hyper-tidal estuary using a widely used numerical model. The numerical model was calibrated against field measured data for various tidal conditions. The model simulated current speeds and directions generally agreed well with the field data. The model was then further developed and applied to study the two transport timescales, namely the exposure time and residence time for the hyper-tidal Severn Estuary. The numerical model predictions showed that the inflow from the River Severn under high flow conditions reduced the residence and exposure times by 1.5 to 3.5% for different tidal ranges and tracer release times. For spring tide conditions, releasing a tracer at high water reduced the residence time and exposure time by 49.0% and 11.9%, respectively, compared to releasing the tracer at low water. For neap tide conditions, releasing at high water reduced the residence time and exposure time by 31.6% and 8.0%, respectively, compared to releasing the tracer at low water level. The return coefficient was found to be vary between 0.75 and 0.88 for the different tidal conditions, which indicates that the returning water effects for different tidal ranges and release times are all relatively high. For all flow and tide conditions, the exposure times were significantly greater than the residence times, which demonstrated that there was a high possibility for water and/or pollutants to re-enter the Severn Estuary after leaving it on an ebb tide. The fractions of water and/or pollutants re-entering the estuary for spring and neap tide conditions were found to be very high, giving 0.75–0.81 for neap tides, and 0.79–0.88 for spring tides. For both the spring and neap tides, the residence and exposure times were lower for high water level release. Spring tide conditions gave significantly lower residence and exposure times. The spatial distribution of exposure and residence times showed that the flow from the River Severn only had a local effect on the upstream part of the estuary, for both the residence and exposure time.

Extreme storm tides in the German Bight (North Sea) and their potential for amplification

Abstract. Storm tides are a major hazard for the German North Sea coasts. For coastal protection and economic activities, planning information on the probability and magnitude of extreme storm tides and their possible future changes is important. This study focuses on the most extreme events and examines whether they could have become more severe under slightly different conditions while still remaining within physical plausibility. In the face of a limited number of observational data on very severe events, an extensive set of model data is used to extract most extreme storm tide events for locations in the German Bight, in particular Borkum and the Ems estuary. The data set includes water levels and respective atmospheric conditions from a hindcast and future climate realizations without sea level rise describing today's and possible future conditions. A number of very severe events with water levels exceeding those measured near Borkum since 1906 are identified in the data set. A possible further amplification of the highest events is investigated by simulating these events for the North Sea with different phase lags between the astronomical tide given at the open model boundaries and the wind forcing. It is found that superposition of spring tide conditions, different timing of the astronomical high water and atmospheric conditions during the highest storm event would cause an enhancement of the highest water level up to about 50 cm. The water levels of the two highest events from the data set are used to analyse the effects in the Ems estuary using a high-resolution model of the German Bight. Additionally, the influences of an extreme river runoff and of sea level rise are studied. The extreme river runoff of 1200 m3 s−1 increases the highest water levels by several decimetres in the narrow upstream part of the Ems estuary. This effect diminishes downstream. The sea level rise increases the water level in the downstream part of the Ems estuary by the amount applied at the model boundary to the North Sea. In the upstream part, its influence on the water level decreases. This study may serve as a first step towards an impact assessment for severe storm tides and towards implications for coastal zone management in times of climate change.

Dynamics of the Estuarine Turbidity Maximum Zone from Landsat-8 Data: The Case of the Maroni River Estuary, French Guiana

The estuarine turbidity maximum (ETM) zone occurs in river estuaries due to the effects of tidal dynamics, density-driven residual circulation and deposition/erosion of fine sediments. Even though tropical river estuaries contribute proportionally more to the sediment supply of coastal areas, the ETM in them has been hardly studied. In this study, surface suspended particulate matter (SPM) determined from OLI (Operational Land Imager)-Landsat 8images was used to gain a better understanding of the spatio-temporal dynamics of the ETM of the tropical Maroni estuary (located on the Guianas coast, South America). A method to estimate the remotely-sensed ETM location and its spatiotemporal evolution between 2013 and 2019 was developed. Each ETM was defined from an envelope of normalized SPM values > 0.6 calculated from images of the estuary. The results show the influence of the well-marked seasonal river discharge and of tides, especially during the dry season. The ETM is located in the middle estuary during low river-flow conditions, whereas it shifts towards the mouth during high river flow. Neap–spring tidal cycles result in a push of the ETM closer to the mouth under spring-tide conditions or even outside the mouth during the rainy season. An increase in SPM, especially since 2017, coincident with an extension of the ETM, is shown to reflect the periodic influence of mud banks originating from the mouth of the Amazon and migrating along the coast towards the Orinoco (Venezuela). These results demonstrate the advantages of ocean color data in an exploratory study of the spatio-temporal dynamics of the ETM of a tropical estuary, such as that of the Maroni.

Small Scales Dynamics Inferred from Tidal Measurements to Mitigate Daily Floodings in the City of Douala: A Case Study of the Besseke's Flood Drain

The recently constructed Besseke’s flood drain is always filled with water due to individual or combined effect of the tide, urbanization drainage, underground plumes and precipitations runoffs. This study focused on the analysis of small scales dynamics inferred from short term tidal measurements to mitigate the daily flooding in the Besseke’s flood drain. The methodology used is based on field measurements observation. The sampling of water level was conducted during two (02) different tidal regimes in May 2019. The volume of brackish water moving in and out of the Besseke’s flood drain was calculated using the formula of O’Brien. The results showed that Spring conditions had greater amplitudes than Neap tide conditions. During Spring tides, the tidal prism that passed in the midsection of the Besseke’s flood drain (S4) was 3.5 × 101 m3. This means that only a negligible amount of the incoming brackish water reaches the Besseke’s flood drain, amplifies and causes the daily flooding. The unexpected stronger amplitudes and dynamics observed in S4 could be due to its sub estuary nature. Furthermore, the percentage composition of water in this section, showed that the fraction of brackish water changes from 85.7% during Spring tide to 77.8% in the Neap tide conditions. The overall spatial evolution revealed that, the trend in tidal prism (during Spring conditions) was (S0) > (S2) > (S1) > (S3) > (S4) with corresponding values of 2.1 × 104, 1.3 ×104, 1.0 × 104, 2.5 × 102 and 3.5 × 101 m3 respectively. Finally, Tidal prism and Cross-sectional area showed a perfect correlation (r2 = 0.96). The best fitted Cross-sectional area-Tidal prism relationship was obtained in S3 (Market) during Spring tide condition.