How Snow on Gallow Ridge Becomes Summer Tap Water

Quarrystone is a fictional town of about 6,000 people at the foot of Gallow Ridge. Its water does not come from a river or a lake. It comes from four wells drilled into a bed of sand and gravel under the valley floor. In July, when weeks pass without rain, the wells still run. To understand why, you have to look at the ridge in January.

Snow falls on Gallow Ridge from November through March. It does not melt right away. Layer settles on layer, and by late winter the snow on the upper slopes can stand taller than a person. Water managers call that stored snow the snowpack. In one sense it is a reservoir, though no one built it and no dam holds it in place. The cold holds it in place instead.

The water in that snow did not start on the ridge. Most of it evaporated from oceans and lakes, rose into the air as vapor, and traveled with the wind. A water molecule spends about nine days in the atmosphere on average before it falls again. When moist air rises over Gallow Ridge, it cools, and the vapor turns into ice crystals. The crystals fall as snow. That short trip through the air is the fastest stage in the whole cycle.

Melting starts in April. Sun warms the surface, and the snowpack begins to release water a little at a time. This slow release matters. Rain that falls on frozen ground in a storm runs downhill in hours. Meltwater arrives over weeks, so it has time to soak in. Some of it does run off into Gallow Creek. The rest works down through the soil, then through cracks in the rock, and finally into the sand and gravel below the valley. Filling that layer with water is called recharge, and a layer of sand and gravel that stores water this way is called an aquifer.

The trip through the ground is slow. Water may take months to move from the base of the ridge to the well field, and in deeper aquifers elsewhere, water can sit for centuries before anyone pumps it. That delay is exactly what Quarrystone depends on, because snow that falls in January reaches the kitchen tap in August rather than in February.

The town measures both ends of that trip. In late winter, a crew hikes to three points on the ridge and measures how deep the snow is and how much water it holds. In summer, an operator records the water level in each well every week. Over the years the two records line up. A deep snowpack tends to be followed by wells that hold steady through August. A thin one tends to be followed by wells that drop.

Timing has begun to matter as much as depth. When a warm spell arrives in March, part of the snowpack melts weeks early. The ground is still hard, so more of that water runs into the creek instead of soaking in. The total snowfall for the year may look normal in the records. The wells still come up short in August, because the water left the ridge before the ground was ready to take it in.

Quarrystone cannot control the weather over Gallow Ridge, yet it can plan around what the ridge reports. The town now sets its summer watering rules in April, once the snow survey is finished, rather than waiting for the wells to fall.

1. Where does Quarrystone's drinking water come from?
2. According to the passage, what does the town measure on the ridge in late winter, and what does it measure in the wells in summer?
3. The passage calls the snowpack a reservoir that no one built. Explain what makes that comparison fit.
4. Why does meltwater soak into the ground more easily than rain from a single storm? Use a detail from the passage in your answer.
5. Explain why a year with normal total snowfall can still leave the wells low in August.
6. The town now sets its summer watering rules in April rather than waiting for the wells to fall. Explain why the snow survey makes that possible, using the strongest evidence from the passage.