Stimulating Understanding of Computational science through Collaboration, Exploration, Experiment, and Discovery for students with Hearing Impairments a collaboration of the Shodor Education Foundation, Inc., Eastern North Carolina School for the Deaf, Barton College, the National Technical Institute for the Deaf, and Interpreters, Inc.
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For Teachers!

A note to teachers

Surface Water Runoff Modeling

This page walks you through the student pages "What does the model look like?" and "What experiment can I do with the
model?"

Background

Notes and answers to student questions.

Surface Water Runoff Modeling

Analysis

Using the model:
The Stella model allows you to enter 4 values: Land Use, Soil Group, Hydrologic Condition, and Rainfall. Clicking under
each of these categories opens a pull down menu. Highlighting your choice enters the value. The Curve Number and
Runoff values in the light blue box are automatically updated.

The model will allow you to discover the effects of different soils and land uses on runoff. Plan a simulation that will
evaluate the effect of different kinds of Land Use. The results of your simulation should allow you to rank the Land
Use from least to most runoff.

Write a description of your simulations. What did you do? Explain how you controlled all of the variables and
systematically changed the Land Use.
Answers will vary. I Set the Conditions to average values: Soil group B, Hydrologic condition Fair. I put rainfall at 5 inches because that is the 25-year storm for many of the states in the Eastern U.S. Then I used the model to calculate the runoff for each of the land uses. I put the values in a spreadsheet and sorted the data in ascending order.
 Oak Aspen 0.6 Sagebrush 0.7 Brush 1 Meadow 1.2 Pinyon Juniper 1.2 Woods 1.3 Woods with grass 1.7 Residential Rural 1.9 Open Urban Space 2 Pasture 2 Herbaceous 2.1 Desert Shrub 2.2 Farmsteads 2.4 Residential Urban 2.4 Row Crops Contoured and Terraced 2.4 Small Grain Contoured 2.4 Small Grain Contoured and Terraced 2.4 Small Grain Straight Row 2.5 Row Crops Contoured 2.8 Row Crops Straight Row 3 Gravel Road 3.4 Industrial 72% impervious 3.7 Paved street with Open Ditch 3.8 Commercial Business 85% impervious 4.1 Parking lots 4.8 Paved Street with Curb 4.8

Group the different Land Uses into 3 groups; Uses with little runoff, medium runoff, most runoff. What characteristics
do the uses within each group share?
Answers will vary. I see 3 groups; runoff from .6 to 1.3 are natural settings with little or no human disturbance. 1.7 to 3 are lands with some human disturbance but the people manage the plant life. 3.4 to 4.8 is intensive human use with little or no plant life.

Using 3 land uses from each of your 3 groups, plan a simulation that will evaluate the effect of different Hydrologic
Conditions on runoff. Explain your results.
Answers will vary. In general  poor hydrologic conditions will have more runoff than good conditions. With increased human impact, the hydrologic conditions become less important because the land has an impervious cover.

Using the same 3 land uses from each of your 3 groups, plan a simulation that will evaluate the effect of different Soil
Answers will vary. In general, group A soils will have less runoff than group D. With increased human impact the soil conditions become less important because the land has an impervious cover. Soil group and hydrologic conditions can have roughly equivalent impacts.

Use the model to determine the runoff from your school in a 25 year storm.

The students will need to measure and calculate the impervious surface area of the school i.e. roofs, parking lots, roads and also measure and calculate the pervious areas i.e. grass, forests, etc. They will need to search the internet or contact local sources to determine the rainfall in a 25 year storm. Putting this into the Excel spreadsheet they can calculate the runoff for each type of area and then the total runoff.

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