Drainage Network Modelling for Water-Sensitive Urban Design

While drainage network models may be relatively easy to assemble as a prerequisite to site selection for infrastructure supporting suburbanisation with Water-Sensitive Urban Design (WSUD), this is unlikely to be the case if the terrain is very subdued. Both ab initio and retro-fit WSUD implementation for such terrain refers, in the first instance, to a drainage network model that includes information on the scope for optimising residential space while conforming to: (1) statutory planning rules about the provision of public open space; and (2) WSUD drainage network design such that runoff waters are retained long enough to allow at least temporary storage. It is shown in this research that a technique applied to condition a LiDAR DEM can accurately model the drainage network of a basin at the land-parcel scale. The drainage network for ab initio WSUD is best defined using multi-flow modelling, with the relative significance of stream segments indicated by their stream order derived using the Strahler method. In contrast, when applying the retro-fit WSUD, the relative significance of segments given by the Shreve stream order method was found to be more useful. The approaches described in this article are designed to support the initial site planning stage and avoid the need for immediate and expensive detailed field survey. At the same time they can be deployed to show how much scope there is for WSUD retro-fit in established housing areas up-stream of an infill development area. Thus, basin-wide appraisal is facilitated and the need for earthmoving is minimised.     

A spatio-temporal assessment and prediction of Ahmedabad’s urban growth between 1990–2030

Journal of Geographical Sciences - Analyzing long term urban growth trends can provide valuable insights into a city’s future growth. This study employs LANDSAT satellite images from 1990,...     

Channel morphodynamics and sediment budget of the Lower Ganga River using a hydrogeomorphological approach

The Ganga River is one of the largest river systems in the world that has built extensive alluvial plains in northern India. The stretch of the Lower Ganga River is vulnerable to siltation because of: (a) the naturally low slope in the alluvial stretch; (b) the confluence of several highly sediment-charged rivers such as the Ghaghra, Gandak, and Kosi; and (c) the reduction in non-monsoon flows because of upstream abstractions of both surface and groundwater. Additionally, the Farakka barrage has impacted the morphology of the Ganga River significantly, both upstream and downstream of the barrage. Large-scale siltation in several reaches has reduced the channel capacity, leading to catastrophic floods in this region even at low discharges. This work has utilized historical remote sensing data and UAV surveys to reconstruct channel morphodynamics and compute sediment volumes accumulated in the channel belt along the Lower Ganga River between Buxar and Farakka. The work was carried out by dividing the total length of the river into four continuous stretches: (a) Buxar–Gandhighat (GW1, 160 km); (b) Gandhighat–Hathidah (GW2, 106 km); (c) Hathidah–Azmabad (GW3, 182 km); and (d) Azmabad–Farakka (GW4, 132 km). We document that major ‘hotspots’ of siltation have developed in several reaches of the Lower Ganga during the last four to five decades. Sediment budgeting using planform maps provides estimates of ‘extractable’ volumes of sediment in GW1, GW2, GW3, and GW4 as 656 ± 48, 706 ± 52, 876 ± 71, and 200 ± 85 Mm³, respectively. These estimates are considerably lower than those computed from the hydrological approach using observed suspended sediment load data, which assumes uniform sedimentation between two stations. Further, our approach provides reach-scale hotspots of aggradation and estimates of extractable sediment volumes, and this can be very useful for river managers to develop a strategic sediment management plan for the given stretch of the Ganga River.