Runoff Around the Planetarium Dome

A Wet Place Beside the Dome

The North Star Planetarium added a paved plaza beside its new dome. Before construction, rainwater collected in a shallow wet hollow near the edge of the grassy area. During four ten-minute watches, students counted adult dragonflies visiting the hollow. They counted 15 visits in all four watches together.

After the plaza was built, part of the grass was covered. Rainwater now ran quickly from the pavement toward the visitor path. The hollow dried sooner than it had before. During four watches held in similar weather, students counted 4 dragonfly visits. They also saw muddy spots on the path after rain.

The planetarium team wanted a solution with two goals. First, the hollow area should receive enough water to support at least 10 dragonfly visits during four watches. Second, the visitor path should be dry on at least 5 of 6 morning checks. The team tested four small designs in similar areas near the plaza. They counted visits and checked the paths in the same way for each design.

Plan A used a shallow basin beside the path. Plan B used a stone channel to carry runoff away from the path. Plan C used a shallow basin and a planted edge between the basin and the path. Plan D used a larger basin that held more water but reached close to the path.