I am testing whether long levee banks (used to protect irrigated land from flooding) have an effect on flood frequency. The null hypothesis would be that the floodwater flows on one side of the levee bank are the same as on the other side.

I have taken 15 random samples of levee banks on the floodplain. For each levee bank sample, I took two 500x100m "paired" adjacent quadrats, one on the river-side and one on the uplands-side with the levee bank in between. Within each quadrat, I counted the percentage of area of flow frequency (for example, 10% of the quadrat area was flooded every year, 39% flooded every 3 years, 18% flooded every 5 years, 5% flooded every 10 years, 28% never flooded).

From my data observations, the quadrats on the uplands-side of the levee bank receive much less water than the quadrats on the river-side. What statistical analysis should I use to quantify this and investigate further into how the flow frequency is affected?

any help would be much appreciated!

cheers