Deltas: a special case, against the no-dividing generality. See, the land part of a delta is pretty much flat as flat can be, as is the water in all the confused tangle of passages. As a teeny bit more sediment is dropped *here* this channel becomes temporarily higher, and more water flows over *there*. Which erodes this bank, curves that meander more, cuts off yonder passage entirely, and bang! New Orleans is no longer a major port. Or would not be, betimes, if the lower Mississippi were left alone. Dredges and dikes fight the current, and put water where mankind wants it- till the next flood, when the river asserts itself and human commerce stages a strategic withdrawal.

Don't think of a delta as what some rivers do before they reach a coast. Instead think of them as what can happen after river water *passes* a coast (lake too, not just ocean). Restricted flow spreads out when the banks are left behind, slows, and drops megatons of sediment. So unless a river lets out into a bay (certainly does happen), figure a delta as sticking outward, not extending ashore.

A river could do a similar thing as it reaches a dry lakebed; spreading out into multiple threads and dropping sediment. That's an alluvial fan - small-scale seen at the base of any steepish mountain. Large-scale you could see such at the edge of a desert (death of a river, a bit rare), or (with water flow continuing on through) any well-watered transition from steep to flat.

Say a river rushes down out of the mountains and hills, and fins itself traversing flat terrain. The flatness could be the river's own fault, after it filled in some steeper sided valley with sediment over the years. In flatter surroundings is when a river will tend to meander. Mind you, headwaters can be crooked, being at the mercy of however valleys intersect. But on the plains or in broad river valleys one year *this* way is temporarily "most down" (maybe by a matter of inches of altitude) and a couple of years later sedimentation and the erosion of banks makes *that* way a little lower. Thus the smooth loops and elbows of the lower Mississippi (and Amazon, and Rhine, and Yangtze...). Draw a river doing that, and you've shown me the land is flat.

Tributaries will be missing if the land a river passes through is dry (see the lower Nile). Lots of rain, then more tributaries - but you needn't show the thick nets you do in some way-upstream headwaters.

Where will there be more or less rain? Oooooh, big subject. A whole series of college courses in fact. A browser and a curious mind will garner enough generalities to achieve decent plausibility though. Think of humidity as being scraped off of passing air masses when crossing mountains. Thus Middles of big continents tend to be drier. By air movement, here we mean prevailing winds, thus you can get wet seasons and dry ones as summer and winter shift all the general highs and lows around. If you don't want to get too detailed, just claim your prevailing winds are like thus-and-so, and written the areas upwind of mountain ranges, and dry out the downwind "rain shadows". All other things being equal, coastal land will be at least somewhat damp - the N African coast and the Namib and Atacama deserts being exceptions based on wind patterns.