Water lab

By approximately how much would the water have to rise to flood Coxtown? (Harrisburg map)

1-20'

If a stream is measured to descend from 100 m to 80 m, over a distance of 2 km, then the gradient is

10 m/km

If a stream is measured to descend from 200 m to 150 m, over a distance of 5 km, then the gradient is

10 m/km

What is the approximate elevation near the State Lunatic Asylum? (Harrisburg map)

400'

Note the creek running through the State Lunatic Asylum, and then trace it back along the channel to its headwaters (where it begins). What is the approximate gradient of that creek from its headwaters to where it enters Paxtown Creek? (Harrisburg map)

48.6 ft/mile The elevation of the headwaters is 480' and the elevation of Paxtown Creek is ~310'. This gives a difference of 170'. The distance between them is ~3.5 miles, giving a gradient of 170'/3.5 miles, or 48.6 ft/mile.

Find the Lutheran Cemetary on the Mt. St. Helen's topo map. By approximately how much would the water have to rise to flood it?

70-80'

Find unit Qls on the St. Helen's geologic map. What rock type might correlate to these sediments?

Breccia - This is the best option for an angular, unsorted sedimentary rock.

The arrow is pointing to what feature of a meandering stream?

Point bar - This is the low energy part of the stream where coarser sediments get trapped.

Based on the type of drainage pattern you're seeing, why does it make sense that there are so many marshy areas on this map? Please explain using stream concepts.

The creeks/small streams are so close together that it affects the land. Braided streams have speedy and recurring variations in the quantity of water it has (changing amounts of water - sometimes a trickle, other times a consistent flow). Therefore, the land is never dry; it is waterlogged. There is also a variable discharge, meaning that the sediment that is left behind on the bars creates a rich soil. Plant roots secure themselves in the rich sedimentary soil. Due to the variation in water flow of the braided stream, the marsh has time to grow and spread.

What type of stream pattern is shown here?

braided - This type of stream forms from coarse sediment and variable discharge.

Observe the St. Helen's maps. What is the primary stream pattern you're seeing here?

braided - there are several different channels that join together and then break apart

The gradient of a stream is calculated by

dividing the change in elevation by the horizontal distance traveled by the stream

The arrow points to what feature of a meandering stream?

oxbow lake - a meander was cut off here

What is the likely origin of Saint Helen's Bar?

sediment trapped in lower energy regions of the river - this is similar to a point bar.

What is the dominant drainage pattern seen on the Harrisburg map?

trellis