====== Drawdown Theis Calculation ======

This tool can be used for estimating draw down calculations e.g. when evaluating extraction permits especially when desiring to establish a new well. In addition, the module can be used as a screening tool within a wide range of groundwater-related tasks, including drinking water, industrial irrigation, geotechnics, soil pollution and more.

==== Requirements ====

**The project set up** \\
It is important that the depth is in meter in the project set up.

=== Data ===

As a minimum you need a potentiometric map added to GeoScene3D as a 2D grid and a pump position. If you already have a potentiometric map, use the “Add data wizard” to add the grid. If not, you can easily interpolate a potentiometric map based on the water table in a well database. Right-click on the well database in the “Object Manager” and go to “Interpolate” and follow the wizard to interpolate a potentiometric map. You can see how to add a pump position in step 1.\\
{{:tutorials:themecalc:41d95d1b8859fcf716822c86c2012d68.png}}

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==== Step 1. Pump position ====

The pump position is representative of an intended pumping well and marks the position for the calculation.\\
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1. In the map window click on the red exclamation mark {{:tutorials:themecalc:29e2427dde35b78cf840b3621d603178.png}}, and then click on the map, where you want the fictive well.\\
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2. The point is added as a cylinder in the “Object Manager” and now visible in 3D and on the map (if you want to remove the point on the map please open the “Layer manager”). You can change the color, radius, and vertical and horizontal placement of the cylinder in the “Object Properties”.\\
{{:tutorials:themecalc:924fed40cff2cdba52f31e1ee13cb7c3.png}}\\
{{:tutorials:themecalc:a908b96651b6bfe10729fd866ad4231b.png}}

==== Step 2. The calculation ====

1. Open the menu “Hydro” and click the “Drawdown Theis Calculation” to open the calculation page.\\
{{:geoscene3d:hydro_calculations:5e54c672d4b1ef94dbc009d8d83d1dfa.png}}\\
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2. Select the different opportunities for pump parameters and output. You can see an explanation of all the functions in the table below.\\
{{:tutorials:themecalc:7380eb6c3c6526ac982e00d29ccf605e.png}}

^Function^Explanation|
|Water Table Grid|In this drop-down menu is a list of the 2D grids added to GeoScene3D. This includes also the terrain and layer surfaces beside the potentiometric map(s). Choose the potentiometric map – either added or interpolated in the project – you wish the Drawdown Theis Calculation based on.|
|Pump Position|Choose the position (e.g. future well position) for the calculation. How to create a new well position is described in Step 1.|
|Flow Rate|Flow rate (m3/hour). Amount of water extracted per hour. GeoScene3D will remember the last applied value.|
|Storage coeff.|Storage coefficient. This value has no unit. GeoScene3D will remember the last applied value.|
|Transmiss. (m2/min)|The transmissivity. (m2/min). GeoScene3D will remember the last applied value.|
|Pumping time (min)|Select the period of pumping time in minutes. GeoScene3D will remember the last applied value.|
|Output Object and Grid|Choose to either generate a new grid file (mark the “New Surface Object” and choose the output directory) or to recalculate and replace an existing surface object (choose the “Replace Existing Surface Object”). If you use the last opportunity please be careful not to overwrite a wrong grid file, as this can not be undone. The file can be chosen in the drop-down menu.|
|Output Map Layer|Add the new or replaced layer to a map. Choose the map in the drop-down menu. You can also choose the color scale. This can also later be changed in the map window.|

==== Step 3A. Results for 1 well position ====

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1. The figure below shows calculations of the potentiometric map with a flow rate value of 40 m3/h, storage coefficient of 0.15 and transmissivity of 1.14 m2/min. The black line is terrain, and the dark blue line the potentiometric map without any information of groundwater extraction. The calculation is then based on a different pumping time.\\
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Blue line: Pumping time: 1 hour\\
Pink line: Pumping time: 96 hours\\
Green line: Pumping time: 672 hours.\\
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{{:tutorials:themecalc:2addb8c9ec7eeaf1d006bf563cc0f79a.png}}

==== Step 3B. Results for 2 well positions ====

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1. When calculating the potentiometric maps for more than one well position, the procedure for well number 2 (and calculation number 2) is as before however the potentiometric map for well number 1 (calculation number 1) is used as the “Water Table Grid”. You can calculate the potentiometric map for as many wells as you like.\\
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2. The figure below shows calculations of the potentiometric map with 2 wells and a flow rate value of 40 m3/h, storage coefficient of 0.15 and transmissivity of 1.14 m2/min. The black line is terrain, and the dark blue line the potentiometric map without any information of groundwater extraction. The calculation is then based on a different pumping time.\\
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Blue line: Pumping time: 1 hour\\
Pink line: Pumping time: 96 hours\\
Green line: Pumping time: 672 hours.\\
{{:tutorials:themecalc:7533af66b55382aed52bc3ac38a64dbf.png}}

==== Step 4. Results in the map window ====

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1. Below you can see an example of a potentiometric map in the map window.\\
{{:tutorials:themecalc:1849660627acaaa93c59958b389d2e83.png}}

==== Step 5. Differential map ====

1. In the toolbox you can calculate a 2D grid showing e.g. the difference between the potentiometric map before and after groundwater extraction. This example is for the 96 hours of pumping.\\
{{:tutorials:themecalc:90d83ff07d052434cfebbc61ee417e18.png}}\\
{{:tutorials:themecalc:57a7ec9dedd8b3a157ea1f81d936b4ac.png}}