An Approach to Identify Urban Waterlogging on a Deltaic Plain using ArcGIS on CHD based Flow Accumulation Models

The gradient for any point on the land surface can be calculated using the digital-elevation model. Some empirical correlations are available to determine the gradient of any points. A few studies were conducted for hilly forest areas to determine the aspect and gradient of various points using computational hydrodynamics (CHD) based techniques. On a plain surface, the accuracy of such techniques was rarely verified. The application of such techniques for a plain surface is also extremely challenging for its small slope. Therefore, the prime objective of the present study is to find out an advanced technique to more accurately determine the gradient of various points on a plain surface which may help in determining the key areas affected by run-off, subsequent flow accumulation, and waterlogging. Here, Kolkata city as a deltaic plain surface is chosen for this study. Upto 600 m × 600 grid sizes are used on the DEM map to calculate the run-off pattern using a D8 algorithm method and second-order, third-order, and fourth-order finite difference techniques of CHD. After finding out the gradient, the run-off pattern is determined from relatively higher to lower gradient points. Based on the run-off pattern, waterlogging points of a plain surface are precisely determined. The results obtained from all the different methods are compared with one other as well as with the actual waterlogging map of Kolkata. It is found that the D8 algorithm and fourth-order finite-difference-technique are the most accurate while determining the waterlogging areas of a plain surface. Next, true gradients of waterlogging points are calculated manually to compare the calculated gradient points using each method. This is also done to determine the relationship and error between the true and calculated gradient of waterlogged points using various statistical analysis methods. The relationship between true and calculated gradients is observed from weak to strong if the D8 algorithm is replaced by the newly introduced fourth-order finite difference technique. Better accuracy and stronger relationships can be achieved by using a smaller grid size.

A Review of Water Resources in Delta State, Nigeria With Emphasis on Hydrogeochemical and Microbial Assessment

This research presents a review on water resources in Delta state, southern part of Nigeria, with emphasis on hydrogeochemical and microbial assessment. It also evaluate factors responsible for water contamination, and their resulting health problems within the study area. To achieve the objective of this study, related articles were downloaded from Google, published article on influence of hydrogeochemical and microbial activities on water resources, these articles were thoroughly studied. Findings from this study revealed that groundwater was more studied than surface water. It was observed that groundwater within the riverine communities are much more prone to pollution when compared to groundwater in upland area. From reviewed article, it was observed that, larger percentage of groundwater showed presence of coliform. Study from reviewed article further suggested that hydrogeochemical processes such as rock water interaction, saltwater intrusion and precipitation influences groundwater quality within the study area especially within Sombreiro-Warri Deltaic Plain Deposit.

Groundwater Conditions and Hydrogeochemistry of the Sombreiro-Warri Deltaic Plain Deposit (Shallow Benin Formation) in the Vicinity of Agbarho, Nigeria

Groundwater conditions and hydrogeochemistry in the Sombreiro-Warri Deltaic Plain deposit at the Agbarho area were described with the aid of data obtained from dug wells. Ten dug wells and two surface water locations were sampled for water quality analysis. Regional groundwater flow is from the northeast to southwest direction with local distortion resulting from sustained groundwater withdrawal in more populated areas of the town. pH in surface water range was from 4.9 to 5.4 and that of groundwater from 3.8 to 5.9. TDS in groundwater and surface water ranges were from 39.6 to 123 mg/L and 9 to 25.6 mg/L, respectively. Two hydrochemical facies, magnesium chloride and sodium chloride facies were defined in this study. The order of abundance of cations are Mg>Na+K>Ca, Na+K>Mg>Ca and Na+K>Ca>Mg and for anions is Cl>HCO3>SO4. This study indicates that the groundwater chemistry is controlled largely by precipitation. Water qualities from the dug wells and surface water are well within the SON permitted levels except faecal coliform occurring at minimal level in two wells and one of the locations on the river.

Halmyris: Geoarchaeology of a fluvial harbour on the Danube Delta (Dobrogea, Romania)

In Northern Dobrogea, north of the Dunavăţ promontory, the Roman fortress of Halmyris was founded in the late 1st century AD on a Getic settlement dating to the middle of the 1st millennium BC, probably associated with a Greek emporium of the Classical and Hellenistic periods. At the time of the foundation of Halmyris, the Danube delta had already prograded several kilometres to the east leading to the progressive retreat of the sea and the formation of a deltaic plain characterised by numerous lakes and river channels. Here, we present the results of a multiproxy study combining sedimentology and palaeoecology to (1) understand the evolution of fluvial landscapes around Halmyris since ca. 8000 years BP and (2) identify the fluvial palaeoenvironments close to the city in Getic/Greek and Roman times, in order to locate and characterise the waterfront and the harbour. Our overriding objective was to improve understanding of human–environment relations in river delta settings. We demonstrate that Halmyris, protected by the Danubian floods due to its location on a palaeo-cliff top, had direct access to the river. A secondary channel of the Saint George, flowing north of the site, has been elucidated between the 7th century BC and the 7th century AD and could have been used as a natural harbour.

Differential subsidence in the urbanised coastal-deltaic plain of the Netherlands

The urbanised peat-rich coastal-deltaic plain of the Netherlands is severely subsiding due to human-induced phreatic groundwater level lowering, as this causes peat layers to compress and oxidise. To determine the potential susceptibility of this area to future subsidence by peat compression and oxidation, the effects of lowering present-day phreatic groundwater levels were quantitatively evaluated using a subsidence model. Input were a 3D geological subsurface voxel-model, modelled phreatic groundwater levels, and functions for peat compression and oxidation. Phreatic groundwater levels were lowered by 0.25 and 0.5m, and the resulting peat compression and oxidation over periods of 15 and 30 years were determined. The model area comprised the major cities Amsterdam and Rotterdam, and their surrounding agricultural lands.The results revealed that for these scenarios agricultural areas may subside between 0.3 and 0.8m; potential subsidence in Amsterdam and Rotterdam is considerably lower, less than 0.4m. This is due to the presence of several metres thick anthropogenic brought-up soils overlying the peat below the urban areas, which has already compressed the peat to a depth below groundwater level, and thus minimises further compression and oxidation. In agricultural areas peat is often situated near the surface, and is therefore highly compressible and prone to oxidation. The averaged subsidence rates for the scenarios range between 7 and 13mma−1, which is corresponds to present-day rates of subsidence in the peat areas of the Netherlands. These results contrast with the trend of coastal-deltaic subsidence in other deltas, with cities subsiding faster than agricultural areas. This difference is explained by the driver of subsidence: in other deltas, subsidence of urban areas is mainly due to deep aquifer extraction, whereas in the Netherlands subsidence is due to phreatic groundwater level lowering.