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Changes

This chapter outlines the more significant changes in the MIKE 1D engine compared to the MIKE URBAN / MOUSE and MIKE 11 engines.

HD – Hydro Dynamics

General changes:

  • Adaptive time stepping algorithm has been redesigned and allows time steps to vary smoothly between a maximum and a minimum time step.

Changes compared to MIKE 11:

  • Differences in bed level at river junctions (branch connection points) are now allowed and handled properly. A free outflow condition is applied on the "high" connecting river when the main river water level is below the free outflow condition.
  • The Flood map functionality has been redesigned and improved. All markers are included in the process to provide better low flow bank maps. Memory consumption has been optimised.
  • Lateral inflow in the form of global/distributed rain or distributed source is added at H grid points. For distributed inflows defined for a chainage interval, the exact chainage values are used to calculate the inflow, independent of the position of the grid points in the model.

Changes compared to MIKE URBAN / MOUSE:

  • An improvement of the calculation of the Basin volume and geometry above ground level has been made.
  • The Node extension (cover) functionality has been improved and unified such that manholes and basins are treated similarly.
  • Improvement of transition between blocking and unblocking of water in a pipe with non-return valve.
  • Improvements have been made for calculation of processed data for user defined cross sections.
  • In natural channels, the resistance is now varied along the branch such that the manning number is interpolated at each grid point.
  • The data type specified in .dfs0 files is now used. If the data type is invalid, the engine will give an error. This is especially relevant for rainfall time series, with a rainfall depth item, usually in millimetre: The data type must be accumulated or step-accumulated; a data type of instantaneous will not be accepted.
  • The soft start for boundary items is applied at the start of the validity interval.
  • The initialization based on outlets flush-in will now not flush past a local maximum along a natural channel.
  • When a pump operates outside the specified pump curve the curve is extended with the last value.
  • The water level in an outlet node will now show the boundary conditions even if this is lower than the free outflow in the connecting pipe. The last water level grid point in the pipe will still show the water level from a free outflow when this exceeds the given boundary condition. This has no effects on the results.
  • With MIKE 1D, applying a valve regulation (only positive flow, or only negative flow) to culverts and weirs considers the branch's flow direction. For example, applying only a positive flow to a structure located on a branch with a negative Flow direction will allow water to flow only in the direction of decreasing chainage values. This is the opposite of what the MIKE 11 Classic engine does. Therefore, before running a MIKE 11 simulation with MIKE 1D, it is necessary to change the flow direction for culverts and weirs, if any Valve regulation is applied and if the branch is set to negative Flow direction.
  • The LTS module has been reengineered and improved. The job-list can be created directly from a RR run, and the RR and HD can be run in parallel. Identification of jobs has been improved, and output capabilities have also been improved.

AD – Advection-Dispersion / transport

General changes:

  • The MIKE 1D AD/Transport module follows the grid point layout of the HD module: Alternating mass and transport grid points in the AD module match the H and Q grid points of the HD module. Both MIKE 11 and MIKE URBAN/MOUSE have an AD "mass" grid point at both H and Q grid points from the HD module and do interpolation and averaging to match between HD and AD calculations.
  • The MIKE 1D AD/Transport scheme for low Courant numbers is using a tailored version of the accurate ULTIMATE-Quickest scheme. For high Courant numbers a less accurate but more stable implicit up-winding method is used.
    • The solution is basically oscillation free, i.e., no over- and under-shooting of values at sharp fronts.
    • Such a combination of schemes can handle all flow conditions.

Changes compared to MIKE URBAN / MOUSE:

  • Additional volume introduced due to volume errors in the HD module is added in MIKE 1D with the concentration of the component, i.e., component concentrations are maintained, but component mass errors are introduced. MIKE URBAN/MOUSE adds additional volume with zero concentration, and thereby maintains the component mass, but not the component concentration.

ST – Sediment Transport

The ST module has been re-engineered and implemented from scratch. It is only supported from within MIKE HYDRO River and MIKE+.

General changes:

  • The MIKE 1D ST module follows the grid point layout of the HD module: Alternating mass and transport grid points in the ST module match the H and Q grid points of the HD module.
  • The MIKE 1D ST for cohesive sediments uses a special version of the AD/Transport scheme that handles the deposition and erosion.
  • The MIKE 1D ST for non-cohesive sediments maintains separate bed load and suspended load calculations. MIKE 11 models non-cohesive suspended load using a bed-load calculation approach.
  • Cohesive and non-cohesive sediments can be mixed, and work together with AD components and MIKE ECO Lab.
  • MIKE 1D ST supports three types of bed layer layout: Fully alluvial mode (0-layer), active layer only mode, and active and passive layer mode. With the active and passive layer mode, it is possible to model fine sediments being trapped by heavier coarse sediments.

MIKE URBAN WQ Process Model

The MIKE URBAN WQ Process Model has been replaced with MIKE ECO Lab support. A MIKE ECO Lab template implementing the MIKE URBAN WQ Process Model is included with the installation. Parameters from the MIKE URBAN WQ Process Model must be transferred to the MIKE ECO Lab parameters.

RR – Rainfall Runoff

General changes:

  • The additional result file from a NAM / RDI simulation includes the same information, but the naming has changed.

Changes compared to MIKE 11:

  • Calibration plot time series in MIKE 11 are stored at every time step of the rainfall runoff simulation and values of the observed data are interpolated to the simulation times. The time series in MIKE 1D are stored at the times of the observed time series, and values of the simulation are interpolated to the observed times.

Changes compared to MIKE URBAN / MOUSE:

  • Catchments are now considered independently of each other and can run with independent time steps. This may give slightly different results in situations where a catchment in previous versions was forced to run with a wet time step due to conditions in another catchment.
  • It is now possible to include catchments in the Rainfall Runoff simulation that are not attached to the network. This is done by setting the connection type to "None" in the catchment connection dialogue. The catchment will be included in the Rainfall Runoff calculation, but the resulting hydrograph is not included in the network calculation.
  • When modelling snow in RDI simulations, the snow storage will now be activated when the temperature is lower or equal to 0.
  • Initial conditions for the first reservoir for overland and interflow are changed to correspond to the initial conditions for the second reservoirs in RDI simulations.
  • The evaporation is now dependent on the snow depth in RDI simulations. Evaporation is neglected if the snow depth is greater than 0. In MIKE URBAN / MOUSE the evaporation was neglected when the temperature was below 0.
  • Different types of catchments can be combined in a single simulation.
  • RR can be run in parallel with HD, i.e., where runoff and catchment discharge are automatically transferred from the RR module to the HD module during the simulation. This works for HD (water), AD (pollutants) and ST (sediments).

Structures

The structure module has been improved and re-engineered. The set of structures is the same, but many improvements and stabilisations have been implemented for each structure individually. The basic behaviour is the same compared with MIKE URBAN / MOUSE and MIKE 11, but the many changes in the code may give deviations in the results, which in special cases can be significantly different.

Since the Release 2022 for energy loss structures a possibility to choose a new computational mode, called a head loss mode, was introduced. The advantage of the head loss mode computations is that it can handle flow conditions where there is no or small head loss over the structure. Currently it is possible to activate such computational mode in MIKE+.

Please refer to MIKE 1D Reference Manual for further details.