Hi,I have tried to compare the water level data from my model with the observed time series data. Values from the model are lower than the observed values in a consistent manner. Which parameter can be helpful to fix this kind of error? I have attached the plot herewith.Thank you.
waterlevelplot.png
If the water level differences appear to be constant between the model and data, the first thing I would check is any vertical datum corrections that have been applied to the model input data or the observation data. That is usually the most likely explanation if there is simply a constant offset between the model and observation data.If you become convinced that isn’t the problem, then let me know what values you are using for AHO and Z0.
HI Tom,vertical datum are same for the model and observed data. I Have used 0.05 for AHO and 0.015 for Z0.Thank you.
OK. If you are sure there are no other offsets that you could apply to the data, then I would suggest increasing Z0 first and seeing if that has any impact.This still looks to me like a datum issue, so I would ensure that one isn’t in NGVD29 or has a different datum offset.
I have seen the results by increasing and decreasing the AHO and Z0 values, but no significant change is seen. I may have done mistakes in preparing elevation input files. I have prepared all the input elevation data based on Low Water Datum (LWD). I have also prepared the observed elevation data in LWD datum. I have not used NAVD88 or NGVD29 datum. LWD measures 173.5m in IGLD85. I have attached one excel file of my bathymetry data. Do I need to fix my data? Please suggest me.Thank you
I would suggest standardizing to NAVD88, and see if that helps you.
When I converted the IGLD85 values to NAVD88 in GIS, the values are similar. Is there any other possibilities for this kind of issue?
What about the water level data for your open boundary? There may be a datum mismatch between the open boundary and the bathymetry data.
water level data for open boundary and bathymetry data are in IGLD which is similar to NAVD88.
I do not think this is a model problem. If parameter values for AHO, and Z0 do not get you any closer to the data, then I suspect there is a reference elevation problem with the data you are comparing to.Is the offset between the data and your model constant or nearly constant? If so, then I would apply that value as a correction factor to your data.
So, do I have to apply the correction factor for my data (which I am comparing with my model data) or do I need to apply correction for the whole input data?
I would suggest applying the correction factor to your data. Have you investigated the setup of the gage which collects that data? There could be an offset or reference elevation which might explain this.The approach I am suggesting here is obviously a last resort since you have not found any datum issues or reference elevation issues with the gage which would explain this difference. I would not suggest it as a general approach.
Ok I will further investigate on my data.Thank you