Script to plot water levels at S-333 and NP206

S333_NP206_stage.R

###
### Script to plot water levels at S-333 and NP206
###

stg <- read.csv("/data_S333_NP206_20180927.csv")


plot(stg$stg.NP206 ~ stg$hw.S333, pch = 19, cex = 0.5, las = 1, xlab = "Stage at S-333 (headwater; ft NGVD29)", ylab = "Stage at NP206 (ft NGVD29)", col = "darkgray")
abline(lm1 <- lm(stg$stg.NP206 ~ stg$hw.S333), col = "blue", lty = 1) 
### estimate stage at NP206 corresponding to Walker's "low trigger" at S-333
low.trigger <- 8.75
NP206.stg   <- low.trigger * coefficients(lm1)[2] + coefficients(lm1)[1]
lines(x = c(low.trigger, low.trigger, 0), y = c(-5, NP206.stg, NP206.stg), col = "blue", lty = 2)

### add red line showing NP-206 marsh surface elevation (5.99' NGVD29)
abline(h = 5.99, col = "red", lty = 2)

Thanks @troyhill for sharing your code...its refreshing to see someone else using R ;)

For efficiency, you can use the predict function in base R to get the NP206 stage value for the S333 HW "low trigger" based on the linear model that you applied. Also you can get fancy and include confidence intervals.

predict(lm1,data.frame(hw.S333=8.75))

#include the confidence interval around the 8.75 value.
predict(lm1,data.frame(hw.S333=8.75),interval="confidence)

Nice, thanks! I didn't realize predict had a confidence interval option. Very useful.