home.md

@@ -4,12 +4,27 @@ It started in jan. 2023 and will gradually catch up with the french projet.
 
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+Of course, every app needs its doc.
+The translation of the french wiki will take some time, but a summary is due soon. We trust that professionnals working in the field of flood management will be able to use it already.
+
 ### First step : draw marbles from a bag to help understand flood probabilities... and use an app to mimick series of draws
 So far, we are working the first step of the project : help to convey messages about **flood probability on a given year** and  **on N years**, because you don't buy a house or design a flood mitigation project for one year.
-This can be achieved by drawing from a bag marbles colour-coded with respect to their probability, that can be understood as this year's flood return period. After this, we can move on to series of N years, and for this an app is very useful to automatically generate series of "floods". 
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+#### Tools : a real bag... and an app
+This can be achieved by drawing from a bag marbles colour-coded with respect to their probability. How can this colour be understood as this year's flood return period ? 
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+This stage is the opportunity to discuss these notions, and understand that colors represent a class of return periods : on a total of 100 marbles:
+- $`\textcolor{green}{ \text{the 8 green marbles}}`$ mean floods with a return period between the 10-yr and the 50-yr return period,
+- $`\textcolor{blue}{ \text{the only blue marble}}`$  represents floods with a return period between the 50-yr and the 100-yr return period, 
+- $`\textcolor{red}{ \text{the red marble}}`$ represents thus $`\textcolor{red}{ \text{all the other, higher floods : floods with a return period OVER 100-yr.}}`$ It means that the reference "100-yr flood" does not occur as such once in 100 years, but it is EXCEEDED once in 100 years.
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+ Check that all these probabilities  ( 8 + 1 + 1 ) / 100 add up to 10/100, meaning the probability of the remaining 90 black marbles is indeed 9/10 : 9 floods in ten are UNDER the the 100-yr return period.
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+After this, we can move on to series of N years, and for this an app is very useful to automatically generate series of "floods". 
 
 The HTML version is not yet as complete as the Python code (in French only so far), but it does provide the results of N draws visually (one token per drawn marble) and as stats (number and empirical frequency for each colour). HTML has the huge advantage to be easier for anyone to use : just download the file and drag-and-drop it in your browser's navigation bar !
 
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 ### Other parts of the project not yet available in English :disappointed: 
 The french "Sac de Crues" project also offers small apps and texts to discuss:
 - interpretation of probabilistic floodmaps with several flood extent maps overlayed one atop the other (more tricky than it seems if the legend is deceivlingly simple ! ) ;