Rainfall Patterns and Drainage Density: The Big

Island of Hawaii•Students are asked to determine the location of river channels on the Big Island of Hawaii.•Students are provided with a rainfall map, a DEM of the island, and a shape file containing the actual locations of rivers.

•WARNINGS:•This project requires ArcMap software, with spatial analyst and a hydrology add-on!•The link where you can download the hydrology extension is: http://support.esri.com/index.cfm?fa=downloads.dataModels.filteredGateway&dmid=15•Nice support page on using the hydro tools at:http://stuff.mit.edu/afs/athena/course/1/1.966/www/Lab5A/•This project is fairly advanced and probably only appropriate near the end of a course.

Goals of this

project:

• Synthesize many geomorphic concepts: rainfall patterns, runoff production, drainage density, hillslope processes, fluvial processes

• Students decide what maps they need to complete the project, and they must create the maps themselves.

• CRITICAL THINKING REQUIRED! No regurgitation of formulas or straight plugging in.

Before starting this project:

• At this point in the course, the students know how to make and interpret topographic, contour, slope, and hillshade maps. They also can make and understand the concept of “blue lines”.

• This was the third and final project in a series of ARC map projects that we did.

• The students were given hand-outs with step-by-step directions on how to make all of the required maps. (I’ll post these if you are interested.)

http://www.bigislanddeals.com/webimages/rainfall.gif - for rainfall map

http://hawaii.wr.usgs.gov/hawaii/data.html - for shape file of blue lines

• Lots of Hawaii GIS data, including a 10 m DEM can be downloaded from: http://www.soest.hawaii.edu/coasts/data/hawaii/dem.html

• I just downloaded from the USGS NED site, http://seamless.usgs.gov/ , but I probably had to do some stitching.

NOTE: My students would get lots of points off for this and the rest of the crappy maps that I am showing you! No north arrow, no legend or title, no scale bar, no location coordinates …

Big Island DEM

Big Island Hillshade

Big Island Slope Map

Contour Map draped on DEM

So what is the threshold drainage area?

Some maps one of my students made.

= 45 km2

= 0.27 km2

= 1.8 km2

What the students handed in:

• Maps illustrating the different drainage area thresholds they chose and why. (If slopes illustrated a change in landform, provide the slope map, etc.)

• Text describing how they used the slope, contour and hillshade maps to determine the locations of rivers.

• Text describing why the map of actual river locations looks different from the maps that they made. Why couldn’t they reproduce the same map?

Some general comments:

• This was the third and final project in a series of ARC map projects that we did.

• The students were given hand-outs with step-by-step directions on how to make all of the required maps.

• None of my students had used ARC before.

• This project was difficult for the students and I had to coach them a bit.

Some more general comments:

• Even though this series of projects was challenging for the students, they all enjoyed using ARC, and I received very good feedback on these projects.

• We did not discuss age gradients across the island, but this could be an added dimension to the project.

• We did not discuss how groundwater contributes to flow in Hawaiian rivers – maybe next time?