Instructions for Running the Pocket Gopher Disturbance Simulation

This program simulates the effects that burrowing by pocket gophers have on the vertical distribution of artifacts and sediments and the disruption of sedimentary structures (stratification) within archaeological deposits. It relies on a model of pocket gopher disturbance I developed intermittently between 1981 and 1986. Details of this model are presented in an article I published in the journal Geoarchaeology (vol. 7, no. 3, pp. 185-208) in 1992 titled Effects of Pocket Gopher Burrowing on Archaeological Deposits: A Simulation Approach. Click here to read about the history of my development of the model.

I wrote the first version of this simulation in 1986 using Turbo Pascal running on a Compaq "lunch box" computer with an 8088 processor, a 5 inch monochrome screen, and a 10 mb hard drive (at the time considered a substantial amount of storage for a pc, most of which had no hard drives at all), and running an early version of DOS. I made substantial changes in the program in 1988 to handle the problem of calculating the percentage of the sediment in each level that had been moved by the simulated burrowing.

This version of the simulation is basically the same as the 1988 version, but I have converted it to JavaScript and added some error handling so that it can be used by a larger audience over the Web. The program runs entirely as a client-side script, so you need only view the source of the simulation web page with your browser to see all of the coding behind the simulation.

The simulation consists of three parts, entering starting values into a form on the left side of the screen, running the simulation by pressing a button located at the bottom of the starting values form, and viewing the results of the simulation in a form located to the right of the starting values form.

Starting Values

To run the simulation, you need to enter the number of years you want the program to simulate and a count of small and large artifacts in each level. Small artifacts include those that are <6cm in maximum dimension, and large artifacts are >6cm in size. I often begin the simulation by assuming that all of the artifacts were deposited on the surface, and only enter values for the first level (0-10cm). However, you may enter any counts in any level you wish as a starting point for the simulation. You do not have to enter a number for zero because the program does that automatically. Be sure that all the values you enter are numbers only, no commas or other non-numeric characters are allowed.

I have built a lot of error handling into the program so you should not have any difficulty getting the starting values right before running the simulation. However, there is one aspect of error handling that I have not dealt with because the nature of JavaScript makes it very difficult. This is checking for the entry of real numbers (numbers with values to the right of the decimal place) into the starting values form instead of integer counts. JavaScript is a loosely typed language that makes no inherent distinction between real numbers and integers. Consequently, if you enter real numbers into the starting values form, the program will round them to the nearest integer for processing in the simulation. This is not the best way to run the simulation so don't do it. Please enter counts as integers into the starting values form.

Also, you do no need to enter any values in the simulation results form because this is where the results of each simulation run are displayed. You will do no damage by entering values on this form because they will just be overwritten by the resulting simulated values. 

Simulated Values

The simulated values are the results of a simulation run given a particular set of starting values. The form reports three values: 1) the vertical distribution of small artifacts; 2) the vertical distribution of large artifacts; and 3) the percentage of material (artifacts and sediment) in each level that has been moved by the simulated burrowing. The artifact values you entered as starting values are converted into percentages during the running of the simulation and then converted back into integer counts for reporting in the simulated values form. Consequently, there may be some rounding error that will result in the simulated values to differ from the starting values by a count of one or two.

Running the Simulation

To run the simulation, simply press the button labeled "Run Simulation" located at the bottom of the starting values form. Before actually running the simulation, the program checks your starting values to make sure they have been supplied properly. If they have not, you will receive a prompt that informs you of the problem and suggests to proper remedy. If your starting values have been entered properly, the simulation will begin running immediately. If the number of years you want the program to run is less than 2000, all you must do is wait until you are signaled that your simulation run is complete and view the values in the simulated values reporting form. If years your are simulating is greater than or equal to 2000, you will receive a prompt that informs you that the program may take a little while to run and to be patient. When you click "ok" on this prompt, the simulation will begin running. Because this is all client-side script, the speed of your connection to the Internet should have no impact on the speed with which the simulation runs. However, if you are running the simulation for more than about 5000 years, some browsers will display a prompt that the script is running slowly and may slow down your system, and asks if you would like to abort. Answer no to this browser prompt unless you have entered an excessively large number of years to simulate (such as 100,000) and have to get on with your life.

To run the simulation multiple time, you need only adjust the starting values and press the "Run Simulation" button again. There is no need to clear the form between each run, but I have supplied a button to do that if you wish. If all you want to do is change the number of years the simulation will run, simply change the years starting value and run the simulation gain, There is no need to alter the artifact starting values to run the simulation again. If you think you are ready, you can click here to go to the simulation Web page.

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