Two identical inflows of sediment- and nutrient-laden water are released from the same upstream source at the same time, seen here from above as two parallel lanes. One crosses a dense-vegetation wetland with slow, winding flow; the other runs down a straight channelized route with nothing to slow it.
settleChance โ timeInSlowZone
nutrientDecay = exp(โk ยท rootExposure)
wetland outflow = lowPass(inflow, ฯ_soil)
channel outflow = inflow
- Sediment settling โ inside the wetland zone particle speed drops sharply and drag lets suspended grit sink out of the water column; on the paved route nothing slows the water so grit stays suspended straight through.
- Nutrient uptake โ passing close to root clusters strips nitrogen/phosphorus from the water at a rate proportional to time spent near vegetation; the paved lane has no roots, so nutrient load leaving equals nutrient load entering.
- Flood buffering โ spongy wetland soil is modelled as a low-pass filter (a "sponge" reservoir) on the storm pulse: it stores the surge and releases it slowly, so the downstream flood peak stays low and spread out. The paved lane passes the pulse straight through as a sharp, high peak.
- Rainfall intensity โ scales the size of the next triggered storm pulse, fed identically into both lanes.