WIP - Pixel Art Map (Help with Rivers?)
I've started myself a pixel-style map of a fairly generic fantasy setting, climate-wise. Other regions will have more interesting parts like jungles and deserts and the like, but for now we can assume that everything is England, just like in most fantasy. The red dots are markers for cities, eventually there will be an easier way to name them. I've thought about doubling the image's size to give myself a little more room to work with. Light green is plains, dark green is forests, blue is water, black is just for outlines at this point.
I have a bit of an issue regarding rivers. I know what rivers can and cannot do, that they will generally end in the ocean and never flow uphill, but I don't have a very firm grasp on how rivers tend to work, especially as they get smaller. The river flowing through the lower forest are barely larger than creeks, as I've been building the forest around them. How much rain does there usually have to be before a river is formed? I know that rivers tend to have winter and summer cycles, the snowmelt powering the former and rain powering the latter, but how do rivers last without constant rain over them?
On a similar note, is my idea sound that forests would generally grow where there are abundant creeks and rivers to support them?
Rivers, lakes, and other bodies of inland water are generally where the water table intersects the surface (there are exceptions, such as desert playas).
Precipitation lands on top of the landscape and percolates downward through any soils. When the soil is saturated, the water moves laterally (get a sponge and pour water on it until it runs off; the same principle is at work here). The location of the saturated area is the water table. When the saturated level rises sufficiently to intersect the surface, it shows as liquid water. If there is a slope, it will flow downhill as a creek, stream, or river (depending on the amount of flowing water). If the water hits a steep drop, it will form rapids; a vertical drop makes for a waterfall. Water in a depression will form a pond or lake.
Areas with thin soils or other soils that can't hold much water (like clay) will tend to have highly seasonal flow patterns that match the rainfall. Areas with thick soils rich in organic material can hold a lot of water and release it more slowly. Evaporation is a critical component of equation, too. The roots of plants tend to hold water in the soil, but the leaves tend to remove it. So to answer you question about rainfall, I recommend that you look at English weather. The Scottish highlands, for example, were pretty much scraped clean in the last Ice Age and there isn't much good soil there except in some of the valleys. Forests tend to congregate in the valleys where there is soil. The south of England has fairly good soils and rainfall, so trees often grow all over the place (except, again, in some of the thin soils over chalky regions).
Thanks, that's pretty helpful. I guess I didn't quite understand how the water table works in practice, and that was keeping me from understanding the rest of it. The examples of forests were good too-- I don't have much grasp of how deciduous forests work, because where I live there's nothing but pines, and the two aren't quite the same in the real world.
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