Mean waterlevels cannot be reproduced for old periods

[veenstrajelmer]

The slotgemiddelden are based on mean water levels, but these cannot be reproduced for old periods because of data gaps.

The data retrieved from the DDL is not complete as documented in Rijkswaterstaat/wm-ws-dl#16, but even when using a validation dia from TK, there are large data gaps for which there are mean waterlevels available in a dataset provided by AB. How were these computed in absence of waterlevel data?

import os
import pandas as pd
import hatyan
import matplotlib.pyplot as plt
plt.close("all")

# read the timeseries provided by TK
dir_data = r"p:\archivedprojects\11208031-010-kenmerkende-waarden-k\work\data_vanRWS_20220805\wetransfer_waterstandsgegevens_2022-08-05_1306"
file_dia_hoek1 = os.path.join(dir_data, r"WATHTE_10min\HOEKVHLD_1.dia")
file_dia_hoek2 = os.path.join(dir_data, r"WATHTE_oud\HOEK_KW.dia")
ts_hoek = hatyan.read_dia([file_dia_hoek1,file_dia_hoek2], block_ids="allstation", station="HOEKVHLD", allow_duplicates=True)

# read the mean water levels provided by AB
file_mean = r"p:\archivedprojects\11208031-010-kenmerkende-waarden-k\work\data_KW-RMM\HOEK_Z.txt"
mean_hw = pd.read_csv(file_mean, sep="\\s+", skiprows=1, names=["datetime","values"])
mean_hw['datetime'] = pd.to_datetime(mean_hw['datetime'].astype(str) +"-01-01")
mean_hw = mean_hw.set_index("datetime")
mean_hw["values"] /= 100

fig,ax = plt.subplots(figsize=(10,5))
ts_hoek["values"].plot(ax=ax, label="tijdreeks")
mean_hw["values"].plot(ax=ax, marker="x", linestyle="", color="r")
ax.set_title("HOEKVHLD")
ax.legend()
ax.grid()
ax.set_xlim(pd.Timestamp("1890-01-01"),pd.Timestamp("2024-01-01"))
fig.tight_layout()

Gives:

[veenstrajelmer]

The computation of mean waterlevels for older periods where no timeseries are available is documented in "De invloed van de bepalingswijze op de berekende gemiddelde zeestand"

This method was also described in paragraph 3.6 of "Kenmerkende waarden kustwateren en grote rivieren" (2013)