Water follows a curved channel. Over time, banks retreat, bends grow and migrate, and sediment builds on abandoned ground. When two banks meet across a narrow neck, the river takes a shorter path and leaves an oxbow lake.
01 / Set the conditionsChoose a starting landscape. Change channel width, bed depth, flow intensity, bank erodibility, or valley geometry. Depth is measured below the local water surface.
02 / Build your floodplainRaise, lower, smooth, or set absolute terrain elevations. Brushes work beneath the water too; use Reveal riverbed to see your bathymetry. Larger banks slow migration. Low sections fill when water can reach them. A raised ridge blocks flow until it is overtopped. Start with Straight channel for a simple five-point line. Use Add point to insert a point halfway along the next section. Delete point reconnects the neighboring points; the inlet and outlet are kept. Use the bold gold guide and numbered handles to move the channel. Arrow keys nudge a selected handle; Delete removes an interior point. A perfectly straight river stays straight until you introduce a bend. Regenerate land while editing restores the old banks and carves the new bed; switch it off to move the guide without changing terrain. Channel edits pause the simulation. Still water is placed in the new bed, and abandoned water is removed; existing oxbow lakes are kept. With land regeneration off, only the low portions of the new route hold water.
03 / Put something at stakeClick to place a house. Click two endpoints for a road or the two land abutments of a bridge. Erosion tracks the full road, the house footprint, and bridge abutments. Bridges may span water safely.
04 / Run and comparePlay, pause, or advance ten model years. Watch the asset timeline for erosion contact and loss. Save the scenario to reopen it; export asset results for a classroom comparison. Play starts both water flow and erosion. Pause freezes both, including existing floodwater. Editing the channel pauses the simulation until you press Play again. Terrain and parameter edits can also be made while paused; their water preview stays inside the channel and existing oxbows. Asset erosion and loss are recorded only while the simulation runs or advances by ten years.
What this model doesCurvature-driven meander migration is coupled to a depth-averaged, local-inertial shallow-water grid. Water storage and shared face fluxes respond to gravity, water-surface gradients, terrain sills, and Manning friction. Connected depressions fill; disconnected basins retain existing water. Dry depressions do not create water on their own. One model year is an arbitrary demonstration timescale. Flow intensity scales a steady simulated inlet discharge. Discharge is volume per second; local speed still changes with channel depth, width, and shape.
Water is routed over the full terrain, including the floodplain. Raising a bed displaces its stored water; lowering a connected area draws water in. Local flow can erode wet ground. Point 1 supplies a steady discharge. The last point is a drain-only outlet that requests the same discharge and removes only water present at that outlet. A dry or blocked outlet can temporarily make outflow smaller than inflow, increasing storage until water reaches the outlet. Both boundary exchanges are measured separately; other domain edges are closed. Water routing and meander evolution use separate accelerated clocks. The grid spacing is approximately 3.3 m and this is a conceptual 2D solver rendered in 3D. It omits rainfall, groundwater, infiltration, evaporation, convective acceleration, sediment conservation, structural engineering, and bridge scour. Use calibrated models and site measurements for engineering decisions.
Elevations use a local datum, horizontal units are meters, and the domain is 600 × 420 m. The inlet and outlet follow the first and last channel points when you move, add, or delete points. Height scale changes the display only. At a neck cutoff, sediment plugs and oxbow isolation are idealized as immediate. Oxbows store water dynamically and can reconnect to surrounding water. Long-term lake infilling is not modeled. During a running simulation, interior fluxes conserve water and the inlet/outlet account for external exchange. Manual edits intentionally replace the channel water preview and reset flow momentum; their added or removed water is tracked separately as edit exchange. This design reset does not advance model time or record asset losses.