Runoff
Runoff is rain or melted snow that flows over land and carries dirt and pollutants into streams.
When you rinse a dirty pan, water flows down the slope and carries food scraps and grease into the drain. The top of the pan is like land, and the drain is like a stream. The dirt and bits of food get picked up by the water as it moves. That is how runoff works -- rain moves down slopes and takes dirt with it into streams.
Explaining runoff by grade level
When it rains on a road or a parking lot, the water flows off the hard ground. It picks up oil, dirt, and trash as it moves. That dirty water ends up in a nearby creek or pond. The creek water gets dirtier each time it rains.
Projects that explore runoff
Rain and snowmelt flowing over land pick up substances from the ground before reaching waterways. This project compares two creeks — Umptanum and Wenas — that both start from the same snowpack and feed into the Yakima River. Wenas Creek passes through more developed land; Umptanum flows through open rangeland. Water samples from each are tested for nitrates, turbidity, and suspended sediment. Wenas Creek showed higher nitrate and turbidity levels, while Umptanum had more suspended sediment. That difference suggests human activity raises certain chemical levels in the waterways nearby.
As water flows over streets and yards and into a river, it picks up pollutants along the way. This project tests whether that pattern shows up in a real river by collecting five samples upstream and five downstream from a populated area. Each sample is tested for pH, turbidity, ammonia, and nitrate content using pH paper, a turbidity meter, and a freshwater test kit. Higher pollutant readings downstream point to runoff from the town changing the water quality as the river passes through.