Biology 235 - Special Topics, Wetlands

Assignment #1

September 24, 1997

Directions: complete the following using your text, lecture notes, any other references, and the calculator, slide rule, or computer of your choice. Answer on separate sheets of paper and show your work. Please do not discuss this assignment with others, however you may ask me for as much assistance as needed. This assignment is due Monday Sept. 29, 1997 however please start work on it soon, since you also have an exam on Sept. 29. This assignment is worth 50 pts.

1. (30 pts.) Suppose you have been assigned to evaluate the following situation. Groundwater contaminated by gasoline (leaked from an underground storage tank) is polluting a 400 m2 wetland (see diagram).

diagram of wetland and river

a. The hydraulic conductivity of the soils on site is 0.1 x 10-5 cm/s. The hydraulic gradient can be determined by noting the height of the water table (GW elevation) at the source of the leak and at the wetland perimeter. These elevations are noted as vertical dashed lines. The size of the contamination "plume" is also indicated.

Using this information and Darcy’s Law, determine the rate at which contaminated groundwater is entering the wetland.

b. The situation is stable and acceptable, providing the gasoline does not enter the nearby river (see diagram). It appears to not enter the river in groundwater, however a surface outflow (ditch) to the river carries contaminated water. This drainage could be treated to remove the pollutant, provided the flow is not greater than 0.4 m3/s. Is that the case?

c. A potential contamination of the river could occur, should the river rise and overtop the levee which separates river from wetland (see diagram). This would happen only in a large flood in which peak runoff exceeds 500 m3/s. Given that the river’s watershed is 0.75 km2 of typical suburban, single-family housing, what rainfall intensity would cause the river to flood the wetland and become contaminated?

 

2. (10 pts.) OVERALL WETLAND WATER BUDGET: compare the following hydrologic budgets (reported in Lent et al 1997. Hydrologic indices for nontidal wetlands. Wetlands 17:19-30) to those of similar wetlands reported in Figure 4-6 of the text. Make water budget diagrams for each (similar to those in Fig 4-6). discuss any differences between these budgets and those of the text.

Wetland Gi Si Pn Go So ET

Phelp’s Marsh, MN 5 18 77 5 47 48

Organic soil bog, MN 5 15 70 9 45 46

Badley Fen Moor, Wales 89 0 11 0 82 18

3. (10 pts.) Evapotranspiration: Snyder and Boyd (1979. ET by Eichhornia crassipes and Typha latifolia. Aquatic Botany 27:217-227) found ET from open pans to be about 6 mm/day and from pans with cattails to be about 8 mm/day. Compare this to the ET predicted by the Thornthwaite Equation (p. 97 in text) for the same location (Auburn, AL). You will need to find the temperature data for Auburn; try the library or the Web. Please provide the source for the data.