Friday, November 27, 2009

Modification of the Hydraulic system in existing Hydram System

Introduction : As we know that the principle of working of hydram is based on change in impulse momentum which is able to lift small quantity of water to relatively higher head using available energy of flowing water at lower head with larger quantity of water. However, the hydram is not getting success up to the optimum potential due to its operational and maintenance problems. Jerk due to up and down of the valve leads to high vibration and frequent breakage of joints / seal and valve itself. This problem can be avoided by replacing snifting box to turbine system and centrifugal pump having pump characteristics of low discharge and high head which can be mounted on the same shaft of the turbine. Part of the excess water from the tails race of the turbine can be stored in a small sump-well in which suction pipe of the centrifugal pump can be lowered.

Principle of the modified hydram is as under :

Power generated by the turbine with available discharge, Q and head, H would be

P = w Q H ηt (1)


w = Unit weight of water

ηt= Efficiency of turbine

Similarly the power required by the pump to lift discharge, q up to height of h would be

P = w x q x h / ηp (2)


w = Unit weight of water

h = head of water to be lifted

ηp= Efficiency of pump

From equation (1) and (2) it is observed that P would be same, neglecting minor losses.

P = w x Q x H x ηt = w q h / ηp

(q/Q) x (h/H) = ηt x ηp

(q/Q) x (h/H) = η (3)


η = Combined efficiency of turbine and pump

i.e. product of the ratio of discharges and ratio of heads would be constant and equal to the combined efficiency of the turbine and pump. The reduction of discharge from Q to q would enable to increase in head from H to h according to principle of conservation of energy if neglect the all losses and product would be equal 1. But in practical, due to energy losses at various stages the product of the above ratios would always less than 1 which will equal to η.

Conclusion and action to be taken : The techno-economic feasibility of the system based on above principle needs to be explored.This will provide a low cost lift irrigation system especially for hilly region for irrigation as well as water supply system and also save huge cost of energy involved for lifting water by two/three stage rising mains from Khad and Nallah having sufficient discharge.

Improvement in Lift Irrigation System with source having turbid water

Introduction : The Sutluj river flow through the middle and lower Himalaya of the Himachal State. High velocity with huge quantity of silt alongwith fluctuation of the water table makes it very difficult for utilization of direct lifting of water both for irrigation as well as drinking purpose. Due to the high turbidity of the water, M/S Naptha Jhakru Hydro-power project in Tehsil Rampur in district Shimla has to shut-off its turbine system for considerable time during the year with a heavy loss of Rs.1.00 crore per day. As an engineer, the considerable CCA which are deprived of irrigation along the river banks can not be ignored due to lack of technology/innovation available for lifting turbid water directly from the river which have considerable amount of turbidity and fluctuation round the year.

Problem : No lift irrigation system is working having the source of water directly from the River Satluj.

Reasons : Once the pumping system is stopped the silt present in the water in the rising main settled down in the vane of the impeller of the centrifugal pump and choke the system. After that, when pump is restarted after considerable of the time, high frictional resistance is developed by the choked silt in the vane of the impeller of the centrifugal pump resulting burning of the motor.

Solution (subject to the technical feasibility) : I think solution lies at a place where the problem arises. i.e. “modification in the priming system of the centrifugal pump”.
  1. The water stagnated in to the rising main after stopping of the pump should be drained out from the suction side of the pumping machinery with automatic valve linked with power cutoff switch.
  2. This will require additional water for re-priming of the pump every time for which a de-silting cum storage tanks can be constructed near the main delivery tank and source water is diverted from the delivery side of the rising main with valve having provision of discharging required amount of the water in the de-silting tank and remaining to the distribution system.

 Parameter for which technical feasibility is to be examined:


  1. Suitable hydraulic/ mechanical valve having electrical/mechanical links with power cut off switch and valve should have good sealing effect to prevent air leakage on suction side.
  2. Alternatively, drain plug/valve may be provided just ahead of the delivery side of the pump for better functioning and it will also avoid leakage on suction side considering priming operation.
  3. Economical size/capacity of the de-silting tanks designed based on Stoke’s law of settlement of the particles and optimum number of the compartments would be required for rotational use according to the permissible residual ppm of the silt content (Optional, if the silt loan in suspension does not effect the priming operation).
  4. Relation between the volume of de-silting tank with volume of the rising main pipe and total head required for the pumping machinery including buffer stock with suitable probability of the number of the priming required for successful operation.
  5. Mechanical/electrical operating system for opening and closing of valve fitted in the rising main for supplying/stopping of water in to de-silting chamber near the main delivery tank.

Benefit of the system :

No additional cost would be required in respect of the civil/electrical/mechanical structures and instruments required for the system. Cost of the rising main varies about 40 to 60 % of the total cost of lift irrigation systems in Himachal Pradesh. The thickness of the rising main pipe is depends on the maximum working pressure and hammer pressure which is developed due to sudden stoppage of the water in the rising main. It is observed from the several DPRs scrutinized by us under RIDF fund since 2003, major constituents of the design pressure is hammer pressure resulting heavy thickness of the pipe is required for the rising main. Due to the sudden opening of the drain plug/valve after modification, will release hammer pressure; resulting thinner rising pipe would be required which will compensate additional cost of the above provisions. (Example : one of the DPR submitted by the Irrigation and Public Health Department of the Government of the Himachal Pradesh for funding under RIDF-XV, namely LIS Pour in Tehsil Sujanpur in district Hamirpur (H.P.) Salient feature of the Schemes is as under ):

CCA : 93.78 Ha

Cost : 201.13 Lakh

Peak water requirement : 41.17 lps

Design discharge : 49.40 lps (for 20 hour pumping )

Velocity of water in economical diameter of the pipe (250 mm ) is 1.01 m/s.

Static head (i/c residual head of 3 m): 23.63 m

Frictional loss : 1.96 m

Total working Head = 23.63 + 1.96 = 25.59

Hammer pressure : 115.00 m

Design pressure : a or b given below whichever is higher

a. 1.5 times of (Static head (i/c residual head of 3 m) + Frictional loss) = 38.59 m

b. 1.5 times of (Hammer pressure + Static head (i/c residual head of 3 m) + Frictional loss) = 140.59

Recommended specification of the pipe : MSERW PIPE ( IS : 3589 – 2001 ) Grade Fe-330, diameter : 250 mm and thickness : 4 mm

It is, therefore, observed that the pipe is designed for 140.59 m against the maximum working head of 38.59 m which is 3.64 times of the working pressure of the system. It is also observed that the hammer pressure constitute about 81.79 % of the total design head this can be curtailed from modification of the priming system of lift irrigation system on above concept.

Round the year irrigation water will be available to the farmers even during considerable silt load in the source.




Monday, November 23, 2009

Water Management System for the fragmented rain-fed command area with stream/nallah with varying dependable discharge over the year using annual HDG

Water Management System for the fragmented rain-fed command area with stream/nallah with varying dependable discharge over the year using annual hydrograph.

A Stream hydrograph and monthly requirements of the typical command area in the State of Himachal Pradesh is given below :

“Myth” in design criteria followed at present in the Himachal Pradesh: The peak water requirements as presented in the above fig drawn for 38 Ha CCA is 38 lps, but the lean period discharge of the given stream is 2 lps only it is therefore, project is being formulated for irrigation potential under the given command, would be only 2 Ha.

Can total irrigation potential of 38 ha CCA be created from the same source ?

Yes, why not through the “water management technique”. Water management technique is a rational method which is not a new concept. It is based on the principal of optimum allocation of available water corresponding to the water requirement and use when it is available and store, when it is excess for future requirement. When the above hydrograph and water requirement is analysed temporally (i.e. monthly water available and monthly water requirement based on time scale), it is observed that the annual volumetric water available is more than the annual water requirement. From the table given below, the excess of water of 302623 cum is more than sufficient to meet annual deficit of 70595 cum. But in the time space water availability is not the time of utilization.

“Water management technique for this problem”. ""Water availability may be staggered on time scale to meet water requirement by temporary water storage in-built in to the distribution system.""

***Why it is beneficial to the Hilly state like Himachal Pradesh**

1. Most of the command area in Himachal Pradesh, especially in the higher reaches, are staggered (i.e. boundary of chak/sub chak is not in continuation). And therefore, Non-command area can be judiciously utilized for construction of temporary storage without any loss of cultivable area.

2. Optimum number with small capacity of storage , distributed over the GCA , is more economical than a few number of heavy capacity of water storage because later would be made of heavy RCC structure.

3. Storage structure near to the farmer’s chak would be conducive for development of individual micro-irrigation system.

4. Much more command area can be brought under irrigation with same availability of water.

5. Costly water harvesting structure which requires much more technical knowledge especially movement of the boulders in the hilly areas and high turbidity can be avoided compared to the simple monthly water discharge measurements for this case.

6. Temporary water storage structure will act as a break pressure tank and this will reduce erosion of CC channel bottom due to the scouring velocity of water which is a common phenomenon on steep slope.

Parameters to be considered while designing the irrigation system

1. Annual Hydrograph of the stream/nallah/khad and its monthly dependable discharge is the prime requirement.

2. Optimum number of the storage tanks based on fragmentation of CCA and site feasibility is the second requirement.

3. Optimum number of the temporary storage system and optimum size of the Chaks will give least cost and high use efficiency with lower operation cost.

4. Capacity of the temporary storage tank should be in proportion to the deficit of the water under each chak individually.

5. Every temporary structure must have one inlet but two outlets. Out of the two, one will be a regulated type at the base of the temporary storage structure and other would be at the top i.e RL of designed water table in the temporary water storage. Regulated outlets would be operated during the lean period of the discharge in the source stream and unregulated outlet will be used for normal flow, when there is sufficient water in the stream/Nallah.

6. During the transition period, when discharge is less in the stream/nallah but still more than what it remain during lean period, additional outlet at a optimum height depending on short-fall may be incorporated in the temporary storage structures . This would serve as an effective check to save the precious water being drained-out uselessly owing to opening of the bottom outlet as per ‘one inlet and two outlet’ design suggested in para 5.

(Note: The term, ‘temporary’ in temporary storage structure, should not be confused with its flexible nature of its construction. It is mainly dealt for the function which it will serve i.e, holding the excess water in surplus period and maintaining the requirement even during lean time. )

Methodology for making reliable/dependable hydrograph (dependable discharge) for designing of water management System:

1) The one year discharge measurement is necessary at the site of probable diversion structure along-with daily/monthly precipitation data received over the catchment in which the proposed stream /Nallah / Khad falls.

2) Frequency analysis of the rainfall data of measured in last 10-15 years and normal rainfall data pertaining to the selected catchments (available with metrological department) can be correlated with annual rainfall and runoff hydrograph obtained at step No.1which will help in formulation expected average hydrograph of the selected catchment.

3) This will give relationship between rainfall (as input) and runoff (hydrograph as output).

4) By putting the dependable rainfall data (analyzed by frequency analysis using Webull’s formulae) as input this will give dependable discharge (dependable hydrograph) for the selected catchments.

5) This would provide the basis of quantifying monthly excess and deficit of water with time scale which would be the deciding criteria for designing temporary water storage system would required in GCA.