topic_hydrology(1grass)

💧 topic_hydrology — the hydrology topic bestie 🫶

okay so. welcome to the hydrology topic, aka the GRASS manual's whole water-girl section. if it flows, pools, erodes, drains, or carries solutes around, there's a module for it in here. grab a snack, we're going through all of them 💖

---

🌊 Modules (the full lineup, no skips, periodt)

• r.basins.fill — generates watershed subbasins as a raster map. subbasins, served fresh ✨
• r.carve — generates stream channels. it literally carves them in, iconic.
• r.drain — traces a flow through an elevation model or a cost surface on a raster map. follow the flow, the flow is the main character. 🦋
• r.fill.dir — filters stuff and generates a depressionless elevation map plus a flow direction map, both from an elevation raster map you give it. no sad little puddle-pits left behind 💅
• r.flow — constructs flowlines. lines that flow. that's it, that's the vibe.
• r.lake — fills a lake at a given point up to a given level. making lakes out of nothing fr fr 🌸
• r.path — traces paths starting from starting points, following the input directions. it just follows instructions, very good girl energy.
• r.sim.sediment — sediment transport and erosion/deposition simulation using the path sampling method (SIMWE). dirt goes on a journey 😭
• r.sim.water — overland flow hydrologic simulation using the path sampling method (SIMWE). water on the move, same method.
• r.solute.transport — numerical calculation program for transient, confined and unconfined solute transport in two dimensions. say that five times fast, lowkey impossible 🫠
• r.stream.extract — performs stream network extraction. pulling the whole stream network out, slay.
• r.terraflow — performs flow computation for massive grids. big grid? she doesn't care. 👑
• r.topidx — creates a topographic index (that's the wetness index) raster map from an elevation raster map. elevation in, wetness out 💧
• r.topmodel — simulates TOPMODEL, which is a physically based hydrologic model. the whole model. yes really.
• r.uslek — computes the USLE Soil Erodibility Factor (K).
• r.usler — computes the USLE R factor, the Rainfall erosivity index.
• r.water.outlet — creates watershed basins from a drainage direction map. outlet goes in, basins come out.
• r.watershed — calculates hydrological parameters and RUSLE factors. the heavyweight, highkey does everything 🔥
• r3.flow — computes 3D flow lines and 3D flow accumulation. 3D! three dimensions! not like the other girls ⭐

---

🔎 See also

check out the matching keyword hydrology if you want even more references — the keyword index is where the extra lore lives, iykyk 🧚

handy ways to nav this whole manual:

• Main index
• Topics index
• Keywords index
• Graphical index
• Full index

---

💌 tiny note: this page is a topic page, so it's basically a little hub — it shows you what's in the hydrology family and points you at the keyword. that's the whole assignment, and she ate.

---

and that's the page bestie, we're done!! 🎀 this loveliness is brought to you by the © 2003-2026 GRASS Development Team, straight out of the GRASS 8.5.0 Reference Manual, and yes the version tag on this page is GRASS 8.5.0 too, keep it consistent periodt 💅 🌈