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.

For Teachers!

A note to teachers

Rain Gardens

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

The student questions are in red. The answers are provided on this page in blue. 

Model1

Notes and answers to student questions.

Open the Water Garden spreadsheet. Clicking on the value under Land Use will open a pull down menu. Select Oak Aspen.

The soil at Shodor is a clay loam mix. The soil is classified C. Select C from the pull down menu under Soil Group.

The Hydrologic Condition deals with the condition of the forest. Good hydrologic condition has leaves, branches and small trees and bushes on the forest floor. Poor hydrologic condition is grazed by cattle and thus has short grass. The pictures of the Shodor lot show un-mowed grass. Select fair from the Hydrologic Condition pull down menu.


A 25 year storm is 6.6 inches of rain in central North Carolina. Select 6.6 from the Rainfall pull down menu.


What is the runoff? 2.1 inches


Use the pull down menu for Predevelopment runoff to enter this number.


Part of the land was left undeveloped. Approximately .3 acres was developed. 


This .3 of an acre is now impervious to water. Change the Land Use to parking lots.


What is the runoff now? 6.4 inches


Use the Developed runoff to enter this runoff.


The light blue box with New Runoff tells you the additional runoff caused by the development. The area effected by development is .3 acres. Use the development pull down menu to enter .3.

The light blue Rain Garden box tells you the area needed to retain this extra water. The model calculates the size of the rain garden by first calculating the volume of extra runoff water. This volume of water needs to be held until it soaks into the soil. The water needs to soak into the soil in less than 3 days or the plants in the rain garden will start to die. If there is standing water for more than 7 days, mosquitoes may mature. The soil type tells the model how fast the water can soak in. If the rain garden soil is type A, the rain garden can drain 24 inches of water. Type B soil can drain 17 inches of water. Type C soil can drain 7 inches. Type D soil can only drain 2 inches of water in 3 days.


How much area is needed for Shodor's rain garden? .2 acres 


Shodor is located on .75 acres. Is there enough land to construct this rain garden on Shodor's property? Yes .75-.3 = .45 acres.


Most of the year, a rain garden is dry and can serve a recreational use. The rain garden could double as a soccer field, nature trail, rose garden etc. During a heavy rain the excess runoff is collected in the rain garden. If the runoff isn't collected it could cause flooding downstream. If the water runs off, it doesn't soak in and replenish the water table. Rain gardens help protect your neighbors downstream and replenish the ground water for wells and springs.

Senario1


A Connie Jones inherited a farm when her aunt died. The farm is 164 + acres in Wilson, North Carolina. The
property is outlined in yellow on the map below. 


The farm has 2 land uses. The dark sections are Oak forests. The underbrush is thick. This indicates a good
hydrologic condition. The light sections are cultivated in row crops. The crops rotate between sweet potatoes,
cucumbers, soybeans, and cotton. The fields are plowed between crops leaving little plant residue. This results in a
fair hydrologic condition.

Connie plans to develop the property two ways. First she could construct a shopping center with a Wall Mart as the
anchor store. The shopping center will be constructed in the western or left yellow area. The second yellow plot, on
the right, is to be a subdivision of houses. There will be 4 houses per acre.


Like many growing communities in flood prone areas Wilson County has recently implemented a new regulation. The
regulation states that new construction must include rain gardens to handle any additional runoff they produce.
Connie has hired your firm to determine if her project requires a rain garden. If a rain garden is required, how big
should it be?


Your office has access to the Soil Survey of Wilson County North Carolina. 


Your report to Connie Jones should include the following:


An explanation of the policy governing storm water runoff and how it will help the city.
Answers will vary. The student should explain that development often results in additional runoff from storms. They could explain that the streams developed over the centuries to handle the runoff from the native forests. When additional water is added to the streams and rivers due to development, flooding can result. In order to protect the citizens, the city requires that developed land not add additional water over the amount that would have entered the drainage system before the development. Rain gardens are an acceptable way to keep the runoff at historical levels. This policy will reduce the incidence and severity of flooding. The rain gardens will also provide additional recreational opportunities. Additional parks and green spaces will enhance the city's ability to attract businesses and families. 

Create a table containing the information you collected concerning the acreage, soils, and runoff potentials. The table should
cover pre and post development, shopping center and residential lands.
Answers will vary since the students need to estimate the number of grid sections of each soil type.

 The Soil Survey of Wilson County North Carolina link provides this table and additional information about the soil types.

Map symbol and soil name	Hydrologic group	High water table in feet	Bedrock depth in inches
GoA - Goldsboro	B	2.0 - 3.0	> 60
GpA - Goldsboro	B	2.0 - 3.0	> 60
NoB - Norfolk	B	4.0 - 6.0	> 60
NuB - Norfolk	B	4.0 - 6.0	> 60
Ra - Rains	C	0 - 1.0	> 60
Rb - Rains	C	0 - 1.0	> 60
Ur - Urban Land	-	-	-

Ra and Rb soils are hydrologic group C. The other soils are group B.

The students need to estimate the number of grid sections of each hydrologic group. Since the soil lines are curved, a single section can contain more than one soil type. Fractional parts of sections need to be determined and added together.

Table of data used in recording the number of grid sections in each soil type and the corresponding acreage.  

						acres per grid
soil type	Wall Mart	acres		acres		5.74
B	0	0.0	3	17.2
C	5	28.7	6	34.4
	Woods		Crop
	Homes	acres		acres
B	0	0.0	4.5	25.8
C	1	5.7	9	51.7
	Woods		Crop

Table of data for Wall Mart site.

				Woods
		Runoff inches	Runoff inches	acres	acres	inches
Soil	acres	Predevelopment	Developed	Rain Garden B	Rain Garden C	Additional runoff
B	0	0	0	0	0	0
C	29	0.8	6.4	9.6	23.2	5.6
				Cropland
B	17	4.4	6.4	2	4.9	2
C	34	5.2	6.4	2.4	5.8	1.2
Total	80			14	33.9

Table of data for residential site.

				woods
		Runoff inches	Runoff inches	acres	acres	inches
Soil	acres	Predevelopment	Developed	Rain Garden B	Rain Garden C	Additional runoff
B	0	0	0	0	0	0
C	6	0.8	4.7	1.4	3.3	3.9
				Cropland
B	26	4.4	3.8	-0.9	-2.2	-0.6
C	52	5.2	4.7	-1.5	-3.7	-0.5
Total	84			-1	-2.6

I put this data into a SPREADSHEET.
A range of rain garden sizes depending on the location and soil type of the garden.

 B  soil rain garden requires 14-1=13 acres. C soil rain garden requires 33.9-2.6=31.3 acres. The total acreage in rain garden needs to be between 13 and 31.3 acres depending where it or they are built. A final decision on this can't be determined because the slope of the land isn't given and the rain garden needs to be downhill from the runoff.

The 2 projects Wall Mart and subdivision are almost the same size 80 and 84 acres. The soil type ratio is comparable Wall Mart B 17/C63, Homes B26/C58 .27 and .45 respectively. The rain gardens required don't seem to reflect this similarity in initial conditions. Ask the students to explain this disparity. The difference is in the runoff from a parking lot and homes. Homes actually have less runoff than croplands. This is in spite of the fact that homes have roofs, driveways, and streets. The lawns encourage a lot more water to soak in than the plowed fields. Discuss with the students the implications of this extra runoff from the farm. The plowed soil doesn't have thick vegetation to protect it from erosion. With additional runoff and little protection it is easy to understand why tons of top soil is removed from farms by erosion every year.

Ask the students to compare the rain garden needed for the land that was oak forest and the crop land both C soil type in the Wall Mart example. The acreage is almost the same 29 and 34 acres. The land converted from forest needs 4 times as much rain garden. The forest is 4 times more effective at absorbing the rain as the cropland is. In the 19th century millions of acres of virgin forest was converted to row crops. Discuss the impact of this historical development on runoff into the Ohio and Mississippi Rivers.

Scenario2

After Connie Jones completed the Wall Mart and subdivision projects she wanted to reinvest her money. Connie is considering the purchase of 141 + acres
in Wilson, North Carolina. The property is outlined in blue on the map below. 

The land is currently oak forest. The underbrush is thick. This indicates a good hydrologic condition.

Connie plans to develop the property as a subdivision of houses. There will be 4 houses per acre.

Like many growing communities in flood prone areas Wilson County has recently implemented a new regulation. The regulation states that new construction
must include rain gardens to handle any additional runoff they produce. Connie has hired your firm to determine if her project requires a rain garden. If a rain
garden is required, how big should it be?


Your office has access to the Soil Survey of Wilson County North Carolina. 


Your report to Connie Jones should include the following:


An explanation of the policy governing storm water runoff and how it will help the city.
Answers will vary. The students should explain that development often results in additional runoff from storms. They could explain that streams have developed over the centuries to handle the runoff from the native forests. When additional water is added to the streams and rivers due to development flooding can result. In order to protect the citizens the city requires that developed land not add additional water over the amount that would have entered the drainage system before the development. Rain gardens are an acceptable way to keep the runoff at historical levels. This policy will reduce the incidence and severity of flooding. The rain gardens will also provide additional recreational opportunities. Additional parks and green spaces will enhance the city's ability to attract businesses and families. 

A table containing the information you collected concerning the acreage, soils, and runoff potentials. The table should cover pre and post development for
the land.
Answers will vary since the students need to estimate the number of grid sections of each soil type.

Ra and Rb soils are hydrologic group C. The other soils are group B.

The students need to estimate the number of grid sections of each hydrologic group. Since the soil lines are curved a single section can contain more than one soil type. Fractional parts of sections need to be determined and added together.

Table of data used in recording the number of grid sections in each soil type and the corresponding acreage.

				acres per section
soil type	sections	acres		5.74
B	14	80.4
C	10.5	60.3
total	24.5	140.6

 

				woods
		Runoff inches	Runoff inches	acres	acres	inches
Soil	acres	Predevelopment	Developed	Rain Garden B	Rain Garden C	Additional runoff
B	81	0.1	3.8	12.6	42.8	3.7
C	60	0.8	4.7	18.6	45.1	3.9
Total	141			31.2	87.9

I put this data into a SPREADSHEET.

A range of rain garden sizes depending on the location and soil type of the garden.

Between 31.2 and 87.9 acres.

Connie plans to sell the lots for $25,000 each. 141 acres times 4 lots per acre is 564 lots. 
What is the gross sales amount Connie expects?
$14,100,000

Connie needs to earn this gross amount in order to pay for the land, make improvements and a profit. If a rain garden is needed she won't be able to sell as
many lots. Connie plans to spread the cost of the lots that aren't sold over the lots that are sold.

Calculate the sale price for each lot when the needed water gardens are built on the different soil groups.

 Rain garden on type B soil 

31.2 acres times $100,000/acre = $3,120,000 worth of lots that aren't being sold. 141 acres - 31.2 acres = 109.8 acres for homes times 4 homes per acre = 439 homes. $14,100,000/439 homes = $32,118.45 an increase of  $7,118.45

Rain garden on type C soil

 87.9 acres times $100,000/acre = $8,790,000 worth of homes aren't being sold.141acres - 87.9 acres =  53.1 acres times 4 homes per acre = 212 homes. $14,100,000/212 homes = $66,509.43 an increase of $41,509.43

Some communities choose to construct part or all of the rain garden on the lot where the runoff originates. This might work for type B soils but type C soils can only accommodate 7 inches of runoff. in a 25 year storm the room and driveway produce a new runoff of 4.3 inches. The rain garden would be most of the yard. Kenneth Potter of the University of Wisconsin has a plan for rain gardens that are 10% of the hard surface of the lot. He constructs leach beds under the rain garden to hold the water until it has time to percolate into the soil. http://www.news.wisc.edu/releases/view.html?id=7385

 
The city of Wilson has agreed to take over the maintenance costs for rain gardens that have a dual recreational value and are deeded to the city. Your report
should include a plan for the rain gardens to meet this city requirement. 
Answers will vary.


Evaluate the impact of the rain gardens on the market value of the lots. Do the rain gardens increase or decrease the price people will be willing to pay for a
lot.

Answers will vary.

Justify your rain garden's recreational use in terms of the market value it adds to the lots.

Answers will vary.

Developed by
The Shodor Education Foundation, Inc.

Copyright © 1999-2001 by The Shodor Education Foundation, Inc.

This project is supported, in part, by the National Science Foundation Opinions expressed are those of the authors and not necessarily those of the National Science Foundation.