How rivers flow

In your book, Our Wondrous World (Chapter 1), we learn that rivers, ponds and lakes are natural sources of freshwater, besides groundwater. They are called surface water, because they are on the surface of the land.

A river often begins its journey up in the mountains and flows down across the land. Your book shows this with mustard seeds. Crumple a sheet of newspaper to make folds, place another sheet over it and press it down into gentle slopes. Then slowly pour mustard seeds onto the highest point. The seeds roll down the slopes, just as water flows downhill, and they gather in the low places, the way water gathers in lakes.

This is what the activity teaches: water flows, stops or curves according to the shape of the land in its path. Where the land slopes down, water flows. Where a hill is in the way, water curves around it. Where the land is low and hollow, water stops and collects.

And flowing water can also change the shape of the land, bit by bit.