Large river confluence numerical model output (NERC grant NE/I023228/1)

The morphodynamics and deposits of a large river confluence were simulated using a physically-based, two-dimensional, numerical model (HSTAR) that represents water flow, sediment transport (for two size fractions; sand and silt), bank erosion and floodplain formation. The model has been described in detail and evaluated elsewhere (Nicholas et al., 2013), and shown to be suitable for representing a range of large sand-bed rivers (Nicholas, 2013). In particular, unit bars, the key building block of sand-bed rivers, are an emergent characteristic of the simulations, resulting directly from patterns of modelled erosion and deposition, although it should be noted that smaller-scale bedforms (e.g. dunes and ripples) are not resolved within the model. HSTAR solves the two-dimensional, depth-averaged, shallow water equations written in conservative form. Model equations are solved on a structured grid (resolution δx, δy) within which each grid cell is defined as either active river bed or floodplain (including vegetated islands). For active river bed cells, total sand transport (bedload and suspended load) is modelled using the Engelund-Hansen (1967) transport law. For hydraulic roughness, a constant Chezy value of 50 m0.5s-1 is used in all channels and 15 m0.5s-1 on vegetated surfaces. The model domain was set-up to be broadly comparable to the confluence of the Jamuna and Ganges rivers in Bangladesh. All simulations were conducted using a model domain 66 km long (x direction) by 48 km wide (y direction). This resulted in a model with 1100 × 800 cells, each measuring 60 m long by 60 m wide. The initial width of the two simulated channels upstream of the confluence was 3.6 km and 1.8 km, respectively, with initial channel width downstream of the confluence being c. 4 km. The planform configuration of the model was also similar to the field site, with the channel downstream of the confluence forming a 27° angle to the axis of the major incoming channel. Bank erosion rates are modelled as the product of the bank gradient, the total rate of sediment transport parallel to the bankline, and a dimensionless bank erodibility constant. To capture the planform change observed in the field, the bank erodibility constant was set to be lower (i.e. stronger banks) for the smaller upstream tributary channel and the channel downstream of the confluence, but higher (i.e. weaker banks) for the larger incoming tributary. Finally, the simulated flow regime was also broadly similar to the field site, with low flow and peak discharges for the larger channel of 4000 m3s-1 and 80000 m3s-1, respectively, to reflect the monsoon-dominated regime. Flows in the smaller channel were 50% of that in the main channel. Simulated inflow conditions consisted of a series of regular symmetrical hydrographs, where discharge (Q ) as a function of time is: Q = Qlow + (Qmax - Qlow) ((1+sin(2?T-?/2))/2)3.5 where T is time normalised by the hydrograph duration (i.e. T increases from 0 to 1 over the course of the hydrograph), Qlow is the low flow discharge, and Qmax is the flood peak discharge. Simulations ran for a sequence of 150 annual flood hydrographs. The data consists of 150 output files, one for each simulated flood event. Each file has 6 columns of data; 1) x coordinate (m) 2) y coordinate (m) 3) elevation (m) - with 999 = no data (effectively, not an active part of the model domain) 4) depth (m) 5) unit discharge in x direction (m^2s^-1) 6) unit discharge in y direction (m^2s^-1)

INSPIRE Implementing rules laying down technical arrangements for the interoperability and harmonisation of Geology

Commission Regulation (EU) No 1089/2010 of 23 November 2010 implementing Directive 2007/2/EC of the European Parliament and of the Council as regards interoperability of spatial data sets and services