7. Water harvesting and recycling

Transcript

Hi friends, In the previous lecture, where in the topic on Watershed Management was dealt, we learnt that the one of the principle of watershed management is to arrest the runoff and also to safely divert the excess water available to the storage points. This water which is stored in the storage points, it can be harvested and can be given for the crops at the critical stages. So in this lecture we will be studying with this objective and with this direction and with the topic ‘Water Harvesting and Recycling’.

What is water harvesting? Water harvesting is defined as the process of collection of the natural precipitation from the prepared watersheds for the beneficial use. It is nothing but water harvesting collecting the surplus water. And it is diverting with the safe velocity to the storage points for use as a beneficial purposes. So whatever the moisture available is diverted to the storage structures in the cropped land, and then it can be used for the beneficial purpose. This is what the water harvesting says. Then the rainfall important component of the dryland crop production. In case of drylands, high intensity dryland rainfall causes 25-30% of the rainfall to be lost as surface runoff. So there is a need for managing the water. Calls for developing water harvesting technologies, suitable to different rainfall, soil and topographic situations.

In case of drylands, whatever the runoff is there, whatever the runoff which is not held back, it will flow as waste and it will not be used for whatever purposes. So whatever runoff is there; with a suitable design, with a suitable procedure, we can divert that runoff water to the storage ponds, and then it can be used for the beneficial purposes. This is what says the concept, ‘water harvesting and recycling’. Then coming to the designing water harvesting structures.

• So how to design
• What are the parameters involved in constructing water harvesting structures?

The catchment and the storage capacity:-

The small catchments may not be able to contribute sufficient water, while very large catchments might lead to the excessive silting of the pond and possibly damage the structure by overflow. In this very large catchments are also not advisable. Even the small catchments are also not advisable. Because small catchable advisements, they won’t hold the water in a large quantity. If the very large catchments are there, they will accumulates; they make the silt to accumulate. So what is the correct size of the catchments. The optimum area of catchments in red soils is one hectare, which can yield around 250 m³ of water. So the optimum catchment area in red soil. The catchment area is one hectare, which can hold around 250 cubic meter of water. So this is the designing or the characteristics about designing and deciding the catchment area.

So moving on to this a farm pond is ideal for the collection of this water. After deciding about the catchment area, the storage structure in a way in the form of farm pond is ideal for storing this water. Then coming to designing. What are the criteria for farm pond construction? Okay we have characterized the design with some factors, and also learnt that farm pond is ideal for storage of this water. So what are the criteria for farm pond construction.

• Number one. Detailed features of the catchment or the watershed area is needed
• Suitable site for the pond is needed
• Possible utilization of the stored water
• Then cost benefit analyses
• And total requirement of water for irrigation/livestock/ domestic use

The detailed features of the catchment and watershed area. We will be getting while deciding the catchment area itself. Then suitable site for the pond. The site for the pond should be in such a way that in addition to rainwater, it should have a provision for runoff water to come and fill up into the pond. That is one of the criteria. So the site selected for the farm pond, is such that there should be a possibility of sufficient runoff water to come and collect in this farm pond. Then possible utilization of the stored water. Okay from runoff water this pond has been filled up. Then what are the possible utilities, that water can be utilized. For that cost-benefit analysis has to be done. And total requirement of water for irrigation/livestock/domestic use.

In one hectare area, how much the total water requirement is there for the irrigation purpose. That is for the crops and also for the livestock, and also for other uses. It has to be calculated. So these are the main criteria for the farm pond construction. You can see in the picture, the farm pond constructions are there. In this the farm pond is there, and nearby fodder crops are there. Besides the farm pond if the fodder crops are there, then the easily, whatever the water available in the farm pond, they can be fed to the fodder crops. So this is also one of the farm pond, wherein the accumulation of silt is being cleared up.

Next coming to the farm pond. In case of a farm pond, storage of water is a challenging task, because we have to avoid seepage losses. How we can avoid the seepage losses? By use of some of the sealants. These sealants may be brick, may be cement, may be tarpaulin sheets. So after construction of the farm ponds, we have to have sealants. Otherwise whatever the water stored in the pond, it cannot be stored for a long time. So use of sealants is a regular feature. So useof sealants for the farm pond. Here you can see that. Cement lining has been done. Here compartmentalization of bunds is done. Here also tarpaulin, the polyethylene sheet is used as a sealant.

Next coming to the water storage in the farm pond. As per the experiences go, even the cost incurred in the cement lining pond. The storage of water will be much higher. As you can see from the figure. The water storage in the pond will be to the rim level. If you calculate the daily evaporation from all these, the daily evaporation from the cement lined pond will be very less, when compared to brick lined or tarpaulin made sealant.

Coming to the use of stored pond water. For what purpose the water stored in the farm pond has to be used. It can be used for protective irrigation to the crops at critical stages. You can see that besides here the farm pond is there. And water is being pumped down. And by using the minisprinklers, the water is collected in the finger millet crop. After that this finger millet crop has been grown luxuriously. In this way the stored farm pond water can be used for the protective irrigation for the crops at critical stages. Because at the critical stages of the crop, if the sufficient moisture is not being given, the crop will incur sufficient yield loss.

So in the critical stages, whatever the water stored in the pond, they can be utilized. So in the use of stored farm pond water, can also be used for the rearing fishes, for quite some time in the rainfall areas, in the rainfall regions whatever the amount stored. That can also be used for rearing the fishes. Then the stored farm pond water can also be used in the Azolla cultivation. Azolla cultivation nowadays getting its own popularity, wherein small water structures are being constructed. And in these constructions, Azolla will be grown. This Azolla will be collected and it will be mixed with the regular feeds, and it will be fed for the cattles.

By the experiences. By the experiments, it has been proved that Azolla used along with the feeds can help in boosting or enhancing the milk production in the cattle. So in this way, whatever the amount of the water stored in the pond, they can be effectively utilized. But designing the catchment area and the suitability of the land for the farm pond area decides the ultimate storage purposes in the farm pond. With this, with the conclusion that farm pond water, whatever the extra runoff water that is being gone as runoff can effectively be controlled, and can be made stored in the farm pond. And whatever the water, whatever the runoff water, that is stored in the farm pond, they can be better utilized for giving protective irrigation for the crops at their critical stages. And yields can be enhanced substantially.

With this I am concluding the topic and the lecture.

Thank You.