Study on Maintenance Dredging for Navigable Depth Assurance in the Macro-tidal Hooghly Estuary

Anthropogenic Activity Effects on Canals Morphology, Case Study: Nile Delta, Egypt

Abstract: Waterways are usually contaminated with wastes from industrial, domestic or irrigation sectors. Organizations in charge have adopted solutions to eliminate this problem; however, the adopted solutions contribute indirectly to modifying canal morphology during maintenance. These are examples of anthropogenic activity, as well as randomly implemented dredging, which expand the canal cross-sections. Egypt is a country which depends on surface irrigation through a huge network of canals. The majority of canals in Egypt are subject to anthropogenic activity which affects their efficiency. This study aims to assess the impact of conjugated instances of anthropogenic activity and dredging on canal morphology and capacity. Five canals were selected in the current study in the Nile Delta, Egypt. These canals are highly affected by two associated factors: anthropogenic activity by users and dredging by the government. The study also aims to determine the effects of a newly adopted policy for saving surface water through restoration of the canals’ originally designed cross-sections. The results showed a clear change in canal morphology, which has increased the volume of water in the affected canals. In some cases, the volume of water has increased by 59%, which could have negative consequences for Egypt’s water resources. Sustainable management of water resources in Egypt requires saving each water droplet, and canal rehabilitation is expected to save about 6.56 million m3/year by the year 2022.

Estuarine facies models; conceptual basis and stratigraphic implications

Abstract: The nature and organization of facies within incised-valley estuaries is controlled by the interplay between marine processes (waves and tides), which generally decrease in intensity up-estuary, and fluvial processes, which decrease in strength down-estuary. All estuaries ideally possess a three-fold (tripartite) structure: an outer, marine-dominated portion where the net bedload transport is headward; a relatively low-energy central zone where there is net bedload convergence; and an inner, river-dominated (but marine-influenced) part where the net transport is seaward. These three zones are not equally developed in all estuaries because of such factors as sediment availability, coastal zone gradient and the stage of estuary evolution. Two distinct but intergradational types of estuaries (wave- and tide-dominated) are recognized on the basis of the dominant marine process. Wave-dominated estuaries typically possess a well-defined tripartite zonation: a marine sand body comprised of barrier, washover, tidal inlet and tidal delta deposits; a fine-grained (generally muddy) central basin; and a bay-head delta that experiences tidal and/or salt-water influence. The marine sand body in tide-dominated estuaries consists of elongate sand bars and broad sand flats that pass headward into a low-sinuosity ("straight") single channel; net sand transport is headward in these areas. The equivalent of the central basin consists of a zone of tight meanders where bedload transport by flood-tidal and river currents is equal in the long term, while the inner, river-dominated zone has a single, low-sinuosity ("straight") channel. These facies models and their conceptual basis provide a practical means of highlighting the differences and similarities between estuaries. They also allow the predication of the stratigraphy of estuarine deposits within a sequence-stratigraphic context.

Estuarine Facies Models: Conceptual Basis and Stratigraphic Implications: PERSPECTIVE

Abstract: The nature and organization of facies within incised-valley estuaries is controlled by the interplay between marine processes (waves and tides), which generally decrease in intensity up-estuary, and fluvial processes, which decrease in strength down-estuary. All estuaries ideally possess a three-fold (tripartite) structure: an outer, marine-dominated portion where the net bedload transport is headward; a relatively low-energy central zone where there is net bedload convergence; and an inner, river-dominated (but marine-influenced) part where the net transport is seaward. These three zones are not equally developed in all estuaries because of such factors as sediment availability, coastal zone gradient and the stage of estuary evolution. Two distinct but intergradational types of estuaries (wave- and tide-dominated) are recognized on the basis of the dominant marine process. Wave-dominated estuaries typically possess a well-defined tripartite zonation: a marine sand body comprised of barrier, washover, tidal inlet and tidal delta deposits; a fine-grained (generally muddy) central basin; and a bay-head delta that experiences tidal and/or salt-water influence. The marine sand body in tide-dominated estuaries consists of elongate sand bars and broad sand flats that pass headward into a low-sinuosity ("straight") single channel; net sand transport is headward in these areas. The equivalent of the central basin consists of a zone of tight meanders where bedload transport by flood-tidal and river currents is equal in the lo g term, while the inner, river-dominated zone has a single, low-sinuosity ("straight") channel. These facies models and their conceptual basis provide a practical means of highlighting the differences and similarities between estuaries. They also allow the predication of the stratigraphy of estuarine deposits within a sequence-stratigraphic context.

Trend of sea level change in the Hugli estuary, India

Abstract: Trends of annual sea level records of four tidal observatories of the Hugli estuary—Sagar, Gangra, Haldia, and Diamond Harbour—are analysed from the records of Permanent Service for Mean Sea Level (PSMSL). The rates of sea level changes for the stations are found to be –3.82, +0.89, +2.43 and +4.85 mm yr respectively, connoting a significant positive relation between landward distances of the stations and the rates of sea level rise. This seems to be mainly controlled by disequilibrium in the morphological state of the landward-narrowing estuary with some contribution from sediment autocompaction. Sea level trends of the Hugli have no apparent relation with erosion and accretion of its tidal islands.

Impact of maintenance dredging on macrobenthic community structure of a tropical estuary

Abstract: This paper demonstrates the impact of maintenance dredging activities on the macrobenthic community structure of a tropical monsoonal estuary (Cochin estuary), located in the southwest coast of India for three consecutive years. The results of the study indicates apparent differences in benthic fauna and sediment characteristics between dredging and non-dredging sites, while most of the hydrographical parameters (temperature, pH, DO and BOD) exhibited inconspicuous variations. The dredging sites were characterized by significantly lower faunal density, biomass, and diversity and sustained distinct benthic faunal communities. The tubificid Oligochaeta, an opportunistic benthic taxon, was highly abundant in the dredging sites along with less density of Mollusca and Amphipoda. Prominent distinctions were evident in the feeding guilds of macrobenthic fauna between the dredging and non-dredging sites. The Benthic Opportunistic Annelida Amphipods Index (BO2A index), an index of benthic habitat quality showed relatively higher values (>0.24), which indicates the prevalence of poor environmental conditions in the dredging locations. The present study reveals the extent of impacts associated with maintenance dredging activities in a tropical estuary, which can be used to formulate effective management strategies for the protection of ecologically and economically significant benthic communities of estuarine ecosystems.

Dredging Maintenance Plan for the Kolkata Port, India

Abstract: The present study reports on a systematic procedure and maintenance plan for conducting dredging activity at the Kolkata port located in the Head Bay region, east coast of India. It is one of the oldest riverine ports in the country constructed by the British East India Company. The port comprises two docks, viz. Kolkata Dock Complex and the Haldia Dock System under the administrative control of the Kolkata Port Trust. The navigation channel located in the Hooghly River accommodates sea-going vessels with 200 GRT with pilotage assistance cruising upstream almost 145 km from Sagar Islands located in Hooghly estuary. The navigation channel experiences high rates of sedimentation being a riverine port. This study investigates the sedimentation rate throughout the navigation channel, identifying zones of high sedimentation rate. The behavioural pattern of tides and currents is analysed using the state-of-the-art ADCIRC model, and wave conditions are simulated using SWAN model. The hydrodynamic information obtained from ADCIRC and SWAN is input to the SEDTRANS model. Based on the intensity of sedimentation, the maintenance plan is proposed for three dredging seasons. On the basis of this scientific rationale and seasonal dredging maintenance procedure, it is anticipated that huge investments involved in the maintenance dredging of this channel can be minimized.