Question
How do I ensure the flow conditions of hydraulic structures are properly calculated?
Answer
Below is a practical checklist to ensure sure that flow conditions at structures are calculated correctly:
Structures invert level should be higher than closest upstream and downstream cross-sections
Structure width must be smaller than both upstream and downstream cross‑sections for all water levels
Structures’ flow area should be much less than the closest upstream and downstream cross-sections (If geometry does not enforce contraction and structure does not impose resistance to flow, then numerical control becomes weak or ill‑posed, in which case consider removing the structure from the model)
Ensure flow width, flow area and conveyance are all monotonically increasing with water level
Upstream and downstream cross‑sections must exist and be close to the structure (actually they should be within the model’s Δx‑max)
Q–h relations should be successfully calculated and reviewed. Always check the structure’s Flow Condition tab after recalculation. If Q/h calculation fails or produces non‑smooth curves, geometry is almost always the cause
Avoid “effective area / hydraulic radius” cross‑section types near structures. MIKE+ expects explicit geometry near structures
Disable recalculation only deliberately. If “Allow for recalculation” is unticked, make sure the stored Q/h curve is valid for the current geometry and levels, otherwise, MIKE+ will use a wrong curve
Avoid dry or near‑dry initial states at structures. Use hotstart files, or small upstream base inflows. This avoids spurious first‑step regime selection and oscillations
Initial conditions must be consistent with boundary conditions. This is especially important for gated structures, culverts, and weirs close to boundaries
FURTHER INFORMATION AND USEFUL LINKS
Manuals and User Guides
MIKE+ Rivers User Guide
MIKE 1D Reference Manual
Training options
MIKE+ – Getting started with river modelling
Self-paced course