Applying conditions to 2 dataframes to perform calculation and store result - how to automate process?

Question

I have two dataframes; a simplified version looks something like the following:

df1 <- data.frame(x = c(rep(c(1:10)), rep(c(9:1))),
                  y = c(200, 183, 166, 144, 117, 80, 65, 33, 14, 0, 6, 15, 37, 65, 92, 123, 156, 182, 200))

df2 <- data.frame(WL = sample(x = 0:200, size = 19, replace = F))

For context, df1 actually represents a river cross-section (x & y) and df2 represents hourly water level measurements (WL).

I would like to create an automated way to calculate the cross-sectional area of the river channel that is filled with water for each water level in df2, and store that area in a new column called area in df2.

The following code shows what I would like to achieve, but as you can see it can get very tedious as my actual water level dataset is huge (hundreds of rows). I would appreciate any help to automate this process:

# package required for calculating area of polygon
library(pracma)

# for the first observation/row in df2:
a <- ifelse(df1$y <= df2$WL[1], df1$y, 0) 
df2$area[1] <- abs(polyarea(df1$x, a)) 

# for the second observation/row in df2:
a <- ifelse(df1$y <= df2$WL[2], df1$y, 0) 
df2$area[2] <- abs(polyarea(df1$x, a))