ESTIMATION OF MONTHLY NATURAL FLOWS IN A HIGHLY DEVELOPED BASIN – the case study of KrishnaAnd

BUILDING FUTURE WATER ASSESMENTS SCENARIOS FROM MONTHLY NATURAL FLOWS IN A HIGHLY DEVELOPED BASIN – the case study of Krishna- Anil D Mohile[1], B K Anand[2]  [1] Consultant, Water Resources, New Delhi. Formerly Chairman

Central Water Commission and Ex-offico, Secretary to Governement of India. Email- anildmohile@yahoo.co.in 

[2] International Water Management Institute (IWMI), New Delhi.

ICID - IAH CPSP StudyApplication of CPSP Model to selected basins in India –

Location of basins

DATA AVAILABILITY

Monthly observed flows, atterminal site

Good

Water developmentinformation

Good

Monthly irrigated area andcrop information

Not sogood

Monthly reservoir levels andstorages

Good

Main Strengths or Advantages       Could work in monthly time steps, not annual       Instead of a single value, or average pattern, could establish a

15 yr. Time series of natural flows1. This could highlight the “negative flow” problem, required relook

at data, and improved credibility of the natural flow series.2. Encompassed annual flow variability, as required in studying the

“over the year “ storages Could establish a computational process, which included

water balances and accountsWe could, thus study the effects of both the developmental and

environmental actions on residual flows. Through this process, we could establish the “limits of utilization”

Limitations of the approach

Did not model the whole land phase of the hydrologic cycle.

Modelled the cycle only regarding anthropogenic changes.

Did not model sub-basins. Used a lumped approach; however averaged irrigation requirements from distributed ET0 and effective rainfall.

Illustration of negative natural flow computation.

Observed flow 200

Add for withdrawals and

reservoir evaporation 1600

Subtract estimated returns 600

Add, exports minus imports 200

Subtract reservoirs depletion 1500

Estimate of natural flow Minus 100

This is not possible. Some data is inaccurate.

How we tackled this problem?

       Allowed large evapotranspiration through anthropogenic swamps. This reduced the returns.       Looked into, and reduced reservoir capacities due to likely sedimentation       Slightly increased irrigated area estimates from Governmental sources.

       Allowed large evapotranspiration through anthropogenic swamps. This reduced the returns.

       Looked into, and redused reservoir capacities due to likely sedimentation       Slightly increased irrigated area estimates from Governmental sources.

“Ultimate utilization” and “ Limits of Utilisation”

In strict hydrologic sense, there is no Utilisation!

Is utilization to be measured as “Withdrawal” or as

“ Consumption”

Utilisation, as withdrawal depends on:

       Availability

       Limits imposed on the use (EFR, legal,etc)

       How you use ( Avoiding wasteful ET, efficiencies,etc.)

We prefer to establish the different limits under each scenario. This is illustrated in our results.

 

RESULTS ABOUT LIMITS OF UTILISATIONKRISHNA BASIN, 2025. UTILISATION AT 75%DepedabilityDomestic and industrial use at the same levelStorage development at same level (Figures in billion cubic meters per year)

Scenario BaU-HD

HD-WM

HD-WM2

WM-EFRL

WM-EFRL&H

Max Possible Withdrawal

65.5 69.9 74.1 51.0 48.4

Max Possible Withdrawal

50.0 48.5 48.1.2 39.2 37.5

Max possible useful consumption

27.5 34.1 31.8 26.4 25.0

ConclusionsBaU-LD: GW regime almost unacceptable. Large fall in Gw table expected.

Bau-HD: GW regime only slightly improved. Increase in irrigated area.

HD-WM2: GW regime considerably improved.

HD-WM:Better GW regime. Improvement in irrigated area, as compared to wm2, is small.

HD-WM-EFRL: GW regime similar to WM2. For maintaining low flows considerable irrigation has to be given up. All water management efforts go towards EFR low maintenance.

HD-WM-EFRL&H: GW regime similar to WM2.. Irrigation benefits less than BaU-LD. Thus all new dam construction and water management efforts go towards EFR.

Conlusions (Contd)1.        Development in basins like Krishna would essentially require additional storages.

2.        The BaU, as a strategy, would work a limited extent. However, the ground water regime would get severely affected. Water level reduction would occur throughout.

3.        Water management improvement through anti water logging measures, drainage improvements and reuse of saved water, appears to be the best option..

4.        Distribution efficiency improvements would give further benefits,but, their quantum does not appear to be very large.

5.        A large price for monitoring EFR would have to be paid in terms of giving up benefits in other uses. This clearly is an issue to be decided through trade-offs, considering societal preferences...

 

Issues for discussion      

 Can we obtain more data about irrigated areas?       Can the irrigated areas be underestimated in Governmental figures?       Can we use the “Limits of Utilisation” approach?