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Doubts / discussions

Doubts / discussions

par Purandare Pradeep,
Nombre de réponses : 5

Kindly consider following questions / doubts

1. Is it correct to say that there is double accounting of water? Once as a surface water  & again as a ground water ?

2. Is it necessary to account for following while determining Runoff

    - presence of dams, weirs, watershed works

    - excessive nalla deepening & widening (course contents do discuss about nalla/river straightening)

    - sand mining

    - uncontrolled exploitation of ground water

3. One generally comes across certain terms while discussing hydrology, for example, yield, dependability, intercepted catchment,blue & green water, e - flow, etc . May be those will be discussed in due course

En réponse à Purandare Pradeep

Re: Doubts / discussions

par Sidhartha Mitra,

Dr Purandare,

It is a great feeling to witness your doubts or rather invitation for discussion. To me also such questions are intriguing. I will try to get close to the topics.

In my view water budgeting/accounting/auditing has a system defined beforehand of the exercise. For eg. watershed/basin and in such case both ground water and surface water is considered within a time frame. If we take one year (annual) temporal scale then the continuous interaction between GW and SW becomes negligible. We take into account of the water measurable in surface (like reservoirs, ponds, lakes, rivers, wetlands, etc and abstractions from them) and under ground (in the aquifer storage and draft/withdrawals through wells) separately after a water year, without considering the daily flux. 

Even if we want to have a water budget equation for a day, mass has to balance and for that we need close and accurate monitoring of water in all forms like rain, reservoir, wetlands, soil moisture, ground water (both dynamic/replenishable and static).

Yes, runoff is the response to rainfall and definitely the presence of dams/weirs (percentage filled up), sediments deposited, abstractions (if it is comparable to the runoff discharge) etc would be determinant for runoff. Hydrological modeling can take care of such issues. These are also to be calibrated/validated in a model.

Dependability, Yield, Return Flow, Green/Blue/Grey Water, e-flow are all established terms. Some of them we will see in this course, some other in the advanced course and of course in internet/good books. We can discuss on each one if you want. But it would be relevant to discuss when we encounter in our course.

Hope I am able to clarify a bit. Still would love to listen from you Sir.

Thanks...

Sidhartha Mitra (Director, NWA and as Facilitator for this course)



En réponse à Purandare Pradeep

Re: Doubts / discussions

par Leela G,

Dear Sir Greetings!

For the first question,

In my view water budgeting & accounting should be done both for SW and GW.SW accounting has been done daily by taking the yield of the particular water structure(using rain gauge),inflow and outflow of the water structure(using rise and fall method the water storage will be assessed) from the begining of water year to end of the water year (e.g july'17 -june'18).

Budgeting will be done based on the water balance statement and the demand.

GW accounting should be done separately,(daily basis) based on rainfall intensity,soil properties etc., as well regular gw level should be checked so that  water drawn and can be assessed.Hence water accounting has to be done separately for SW & GW.

For the second question.

Yes,we have to consider the dams,weirs and watershed works to determine runoff.ofcourse weirs and reservoirs are used to gauge the rainfall or snow melt(based on size). As well watershed drainage patterns will play a role in determing runoff

as well as deepening  & widening of  nalla  has to be taken into account . The runoff speed, both overland and in drainage channels, depends to a large extent upon channel and land slope.

 

Sand Mining within or near riverbed has a direct impact on the stream's physical characteristics, such as channel geometry, bed elevation, substratum composition and stability, in-stream roughness of the bed, flow velocity, discharge capacity, sediment transport capacity, turbidity, temperature etc. Alteration or modification of the above attributes may cause hazardous impact on ecological equilibrium of riverine regime.which will influence the run off.

Uncontrolled GW pumping:

Lowering of ground water table in the flood plain because of lowering of riverbed level as well as river water level takes place because of extraction and draining out of excessive ground water from the adjacent areas. So, if a floodplain aquifer drains to the stream  the base flow can be affected  as a result of uncontrolled  pumping.Excessive pumping of ground water in the process of mining in abandoned channels depletes ground water causing scarcity of irrigation and drinking water. In extreme cases it may create ground fissures and subsidence in adjacent areas. 

Sir,this is my view out of little knowldge acquired.Hope you would have clearly explain.Eagerly waiting Sir.

Thank you Sir

Leela.G (Participant of IDL)

 


En réponse à Leela G

Re: Doubts / discussions

par Purandare Pradeep,

I am grateful to Dr Sidharatha Mitra, Director, NWA & Leela G, participant for their prompt & apt replies. The points they have made are valid & helped me a lot in improving my understanding of the subject. Just for continuing the discussions further, I would like to draw attention towards an article in EPW. Its details are given below. Thanks. Regards.

Home » Journal » Vol. 52, Issue No. 31, 05 Aug, 2017 » From Groundwater Regulation to Integrated Water Management
The Biophysical Case

En réponse à Purandare Pradeep

Re: Doubts / discussions

par Sidhartha Mitra,

Recently I worked with Dr Veena Srinivasan the author of the paper you mentioned above (from ATREE) in water budgeting under National Water Mission. There only we discussed, understood and now quite confident on the topics you raised.

Naturally, water year starts from 1st June and then the GWT is lowest, soil moisture minimum and reservoir storage least. So interaction between GW and SW subjected to minimum fluctuation and cycle repeats after water year. So annual water budget is free from the error of double counting. Also storage is measured at the start and end but other flows are measured round the year for water balance. And lastly, if our measurement time required is fast enough compared to rate of transfer from GW to SW and vice versa then least chance of double counting.

Hope I am able to give some new dimension to your query.

Thanks a lot.

Sidhartha Mitra.

En réponse à Purandare Pradeep

Re: Doubts / discussions

par Arasu A Meenakshi Sundara,

Dr. Purandare Pradeep

we are doing only a stock taking exercise in water budgeting and what we get is the question and where it goes is the answer. it takes care of surface water + ground water +other things also.

the second question is a site specific question and only here all the irrigation models fail. if you can embed the real condition then automatically everything will be taken care of. but the should be site specific and if properly integrated the model is likely to give the correct quantity. (Even the hydrological model of GIS and SWAT will not give the same value.)

the third part the participants can discuss in the forum and with the help of experts we can make this more lively and useful