## April 20, 2018

### Rivers I

Some sorta connected thoughts about rivers:

• Obviously rivers flow from high to low [citation needed].
• On the map, each river's drainage (the total amount of area that drains into it) can be represented by the width of the stroke.
• However, drainage is not the same for various amounts of precipitation. In the desert, it might take a lot more hexes ($\equiv$ area) to produce 1 "point" of drainage.
• Therefore, when creating the rivers, each hex can keep track of the raw drainage number. Then multiply by a factor that considers precipitation.
• In real life, this number would be modified by soil type, rock bed composition, etc. I don't think I'm to that point of detail yet. I don't think I'll ever be. Probably.
• Keep track of which hexes have been sources for rivers (drainage = 1)?
• Interestingly, this method creates tons of endorheic drainage basins (drainage basins that do not drain to the ocean). They have no natural outflow. If precipitation is high enough, the river will carve a path through the surrounding terrain to get to lower ground. Alternatively, a lake will form and fill the terrain to the point where it can find an outlet. Sometimes, water just can't get out of the area, so it forms a lake which maintains its level either through seeping into the ground or by evaporation in certain atmospheric conditions.
• I can remove almost all of those basins, and I think I will. Perhaps I'll let it slide if it's a certain distance from the coast. But for now, it's quicker to just raise the area a bit so the water can drain out. All water leads to the sea, so far.
• The more correct way to handle the basin is to check the evaporation rate and balance that against seepage and inflows. That may be on down the line.
• Once this is done, we can apply a bit of geology to erode down the landscape based on how much river is flowing through a hex.
• Terrain generation using procedural models based on hydrology