Hello Everyone !!!
im working on Hydrologic Rainfall Runoff Modelling, for validation of model we need the runoff which is uncontrolled but what actually happens is if suppose there is discharge gauging station which is located to the downstream of any big Dam then they will open the gate only when DAM requirement is fulfilled hence gauge located downstream of that Dam may not be having actual discharge because of rainfall its having controlled discharge controlled by Dam Authorities. My question is how to correct the downstream gauging discharge for validation of RR model?
hI..
In my opinion, Correction of downstream gauging discharge is not logical.Actually it is the major problem in most of the Indian river basin. What you can do in such cases try to get the reservoir operation policy from the authority and with the help of any hydrological model you can do modelling including reservoir operation.
Other option can be calibration and validation of the model before the construction of dam and you can prepared the discharge data after the dam construction, if you are working in climate change than the prepared data can be of much useful.
Another option would be if your dam is not big,try to neutralize the effect of reservoir in calibration of rainfall-runoff model.
The way I see it there are two ways of doing this. First is creating something commonly known as "Naturalized flow" of the system. You can create that if you have longer time series before and after the construction of the dam. You can use statistical methods like detrending the time series after the construction of the dam to match the 1st and 2nd order moments of the timeseries before the construction of the dam and other techniques to remove the effect of the dam. The Second is to use RR models with the capability to model dams with simplified operations. SWAT for example has got a very simple way of modeling dam operations as well away to account for reservoir area rainfall and evaporation.
I would recommend creation of a "virtual" gauge/station upstream the reservoir and to model the reservoir separately though combined routing and water balance approaches for which a minimum information about the geometry of the reservoir is necessary. Many river hydraulicssoftware (MIKE11, TELEMAC or Hydroworks) cope with such problem.
You need to naturalise the flow to remove the effect of dam operation. Numerous techniques are available in the literature, like, tree ring approach are there to do naturalisation. I hope this would help you to meet your problem.
Such problem exist in studying the rainfall-runoff aspect in the downstream of Hirakud dam in Odisha. Of course in the main channel it is not going to give a very good understanding about the r-r relationship, however, you can model the r-r relationship in all the tributaries contributing to the main river, If the downstream tributaries are free from storage system. Or else other situations like naturalise or situation before the dam construction will not of much help considering in some cases considerable time has elapsed and many physical parameters have already been changed during this time.
For a complete solution, I will recommend to work on three steps and then use a hydraulic model to integrate the data and operational procedures. First, develop rain-runoff relationships for all tributaries (as Bitanjaya Das). Second, calibrate the rule-curve (or gauge-discharge) for the dam (which is normally available for the reservoir operations). Third, empirically develop a rating-curve for the downstream gauge. A modular model can be developed to integrate above mentioned three steps. the simulation results can be used to relate accumulated runoff with downstream gauge for the selected reservoir level.
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