Cracking dams intro

Worksheet

for the Intermediate level
on gravity dams



1. Bookmark the Webquest and assign roles. Return to the Process on the web.


2. Use the link on the web to go to the National Inventory of Dams and search for a gravity dam (type=PG) in your county. If there is not one in your county, search for a gravity dam in your state.
To search the database:
Click on Getting Started
Click on the [+] next to Search in the left column.
Click on By General Info.
Scroll down to Dam Type. Select Gravity.
Click on By Loc Info in the left column.
Fill in the State. Fill in the County (these are two separate fields).
Move down the page and click on the Search button.
Once the results appear, choose a dam for your group and click on its name to learn more about it.
If no results were returned, search in your State by repeating the steps without filling in the County. Return to the Process on the web.

3. Once you have found a gravity dam, fill this table in with information about the dam. ***There is a key for the symbols at the end of the worksheet.***

dam name .
river .
city, state .
purposes .
NID height (in feet) .
d.s. hazard pot. .
emerg. action plan .

Return to the Process on the web.


4. What are the purposes of your dam? ***Use the key at the end of the worksheet.





Return to the Process on the web. What are two other services that dams can provide? (Find this on the website.)





Of these services, what does your group think are the most important services a dam provides?




5. Return to the Process on the web. What are two examples of problems that dams cause? (from website)






6. You must gather the tools to do a simulation of cracking in a dam. Return to the Process on the web. From the Gravity Dams section, you must find three tools:
  • Tool #1: how to draw a cross-section of your dam. A cross-section is a two-dimensional slice through the dam -- the dimensions of the dam that you see are the height of the dam and the width of the dam (and not the length of the dam). You must find what the shape of the cross-section looks like. Choose a basic shape for your dam.

    From the information you gathered about the dam, you know the height but not the width of the base or the crest. Find the simple formulas for calculating the base and crest widths (in feet) of the dam in the gravity dams section.

    base width =

    crest width =


    Now, sketch a scale model of your dam using the basic shape you chose and the dimensions you calculated.

    ... .... ... ... ...
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    ... .... ... ... ...
    ... .... ... ... ...
    ... .... ... ... ...
    ... .... ... ... ...
    ... .... ... ... ...
    ... .... ... ... ...
    ... .... ... ... ...
    ... .... ... ... ...
    ... .... ... ... ...
    ... .... ... ... ...



  • Tool #2: how is the dam attached to the ground. Find this tool in the Gravity Dams section. Show where the dam is attached to the ground on your sketch of the dam.

  • Tool #3: what are the forces on the dam. For this simulation, you should apply two forces, the weight of the concrete of the dam and the force of the water in the reservoir. From the Gravity Dams section, you should learn where these forces act on the dam for your simulation.

    • Show these forces on the sketch of your dam in the places where they act.



    7. Return to the Process on the web. What is concrete made of?






    8. Return to the Process on the web. From the Cracks section, you must find two more tools for your simulation.
  • Tool #4: where do gravity dams usually crack. You must find this location in the Cracks section. Once you have found it, sketch a crack on your dam in this place. The crack must start from the outside edge of the dam

  • Tool #5: what do the simulation results mean.

    What does the simulation return to you?



    What do these results tell you?



    •

    9. Return to the Process on the web. In the Simulation section, review the steps of performing a simulation of cracking in a dam. Then move on to the next page to do the simulation yourself. Be sure to watch the movies on how to perform each step.

    Attach the dam as you have attached it to the ground in your sketch.

    Add the loads that you have drawn on your dam: for the weight of the concrete, use 10; for the force of the reservoir water, use 30. Add them to your computer model in the appropriate places.

    Add the crack you have sketched on your dam.

    Simulate!


    10. In what direction did your crack grow?



    Post your answer on the bulletin board under the heading "Simulation Results" about the results of your simulation. There is a link to the bulletin board from the Process section step 10 of the Webquest.


    11. Return to the Process on the web. Find the population of the city nearest your dam in the National Census Bureau. There is a link to the Census Bureau database from Process step #11.

    What is the population?



    Return to the Process on the web. Use the city population as the number of people at risk in Brown and Graham's algorithm. Try out the algorithm for three different warning times: one hour, 2 hours, and some time great than 2 hours. Also try each one with a landscape of a canyon and then of a plain. Fill your estimates in the table below.

    Estimates of loss of life: Brown and Graham's formula
    .warning time
    landscape 1 hour 2 hours ____ hours
    canyon ...
    plain ...



    Which combination of time and place caused the greatest loss of life? The least? Why do you think this is the case?





    What else would you take into account in the loss of life estimation for a dam failure?





    Post your answer on the bulletin board. There is a link to the bulletin board from #11 in the process section of the Webquest.


    12. Considering:
  • the services dams provide
  • the impact dams have on the environment
  • and the fact that dams crack,
    •  your group must answer these two questions:
  • If a dam is cracked, how can you use computer simulations to help you figure out what to do about it?




  • If a dam provides people with power or drinking water but it is also killing fish, do you think the dam should be removed so the fish will live?




    • Post your answer on the bulletin board under "Using simulations" for the first one and under "Social and Ecological impacts of dams" for the second one. There is a link to the bulletin board from #10 in the process section of the Webquest.


    Key for the NID database
    Dam Type PurposeHazard Pot. Emerg. Action Plan
    RE - Rockfill I - Irrigation L - Low Y - yes
    PG - Gravity H - Hydroelectric H - High N - no
    CD - Buttress C - Flood and storm control S - Significant NR - not required
    VA - Arch N - Navigation . .
    MV - Multi-Arch S - Water supply . .
    CN - Concrete R - Recreation . .
    MS - Masonry P - Fire protection, small farm pond . .
    ST - Stone F - Fish & wildlife pond . .
    TC - Timber Crib Debris control . .
    OT - Other T - Tailings . .
    . O -Other . .