Obert Chifamba
Agri-Insight
News that the country has so far recorded rainfall amounts grossing an average of 1 000 millimetres — the highest in five years — should naturally add impetus to preparations for this year’s winter wheat programme and even attract more débutante growers.

The other positive development is that the Zimbabwe National Water Authority (Zinwa) has also confirmed that dam levels across the country are rising with most dams at various stages of filling up, which means one of the most important ingredients for the successful production of wheat looks set to be readily available when the time comes.

It also means there will be something for livestock that has been among the hardest hit each time there are water shortages, as there will be very little or even nothing to eat or drink.

However, as all stakeholders in the agriculture sector revel at what is currently happening, it is critical to remember that more could have been added to whatever amounts of water that will collect in all of the country’s reservoirs this season if they had aided the process by practising water harvesting.

Rainwater harvesting is defined as a method for inducing, collecting, storing and conserving local surface run-off for agriculture in arid and semi-arid regions (Boers and Ben-Asher, 1982).

Harvested rainwater can be put to various agricultural uses while in some cases it can also be for human consumption.

Farmers can always use it for watering gardens or even crops in fields in the event that the season ends abruptly after a promising start in which the rains would have fallen lavishly.

The use of harvested rainwater reduces dependence on other sources of water supply, thus saving farmers from the unenviable task of sometimes forking out money to secure the precious resource from those that have it stocked somewhere.

This also saves them from the hassle of deploying other crucial resources such as labour and time towards going all out in search of water.

This year, for instance, has seen a lot of run-off water making its way to various destinations from fields, sloping hill tops, grazing lands and many other sources but not much, if anything, was done to trap that water for future use.

Millions of cubic metres of water have made their way into oceans through our rivers and did very little to benefit agriculture.

Farmers should have taken advantage of the abundant rains to harvest run-off water from various large areas that in most cases are at an appreciable distance from where it will be used in the future.

Most of the time, this water will be used for irrigation or livestock consumption, which saves the animals from travelling long distances in search of water when they should be resting or grazing.

In most cases, run-off which occurs on hill-top (with stone outcrops), sloping grounds, grazing lands or other compacted areas flow and naturally collect on low lying flat areas and some farmers have even taken advantage of that situation to grow their crops on the wetted part of the landscape and use the run-off without any further manipulation or management.

However, where the run-off is not high, farmers can still construct earth basins that assist in holding the water and increasing infiltration into the soil.

These basins (bunds) are important when the cropped area is not at the bottom of the landscape although they can also still be used to facilitate the distribution of the water even if the cultivated area is on flat land.

There have been reports of cropped tracts of fields and in some cases, livestock being washed away by flash floods this season, a development that makes it even more critical for farmers to have structures that can reduce such heavy flows of run-off and have it contained somewhere.

If they are to build small weirs or dams, then they should make sure there are no flows structurally that may leave the structure prone to bursting under the pressure of the gathering water.

Farmers can always argue that they do not have resources, but in cases where they are doing projects in groups, for example, irrigation schemes, there is nothing to stop them from pooling resources and doing it.

Government recently mandated the Agricultural Rural Development Authority (ARDA) with supervising irrigation schemes and the board has since started looking for 450 irrigation managers to work with irrigation projects and boost production.

And since the world is in a climate change era where either intense rainfall can fall or droughts may occur, it is crucial for all rainwater that is received to be fully utilised.

Heavy rains on their part can damage agricultural land areas, so rainwater harvesting can be used to divert heavy rainfall from reaching agricultural lands, thereby protecting crop plants from getting damaged.

Furthermore, the use of water from rainwater harvesting can help to reduce operating costs since the water is soft by nature in terms of its chemical combinations.

This is so because calcium carbonate from hard water normally piles up in pumps or sprinklers causing blockages and when such equipment is blocked, money is used to unblock their pathways.

On the one hand, such problems are not usually associated with the use of soft water in farming operations, thus reducing the cost to maintain crops.

Also, rainwater can be used as a source of drinking water for livestock and is even more suitable for the purpose compared to the chlorinated water that they end up being given by the farmers to save them from dying due to dehydration.

The good thing about water harvesting is that it can be done through many different ways.

Farmers can use techniques that directly supply run-off water from its catchment to the crop allowing the water to accumulate around the plants before infiltrating into the soil where it is stored in the crop root zone.

These are called micro-catchment techniques, because the run-off-yielding catchments are usually small and directly adjacent to the targeted crop.

There are also macro-catchment techniques, which concentrate rainwater run-off flowing in a temporary natural or man-made channel and store it in a prepared storage facility (such as a reservoir) for subsequent beneficial use.

This category also includes macro-catchment techniques in which water is diverted (by proper damming or cross-structure) out of the channel to inundate nearby lands.

They can also do flood-water harvesting within the stream bed in which case they make use of barriers such as permeable stone dams to block the water flow and spread it on an adjacent plain and enhance infiltration.

The wetted area is then used for crop production.

There is also a system that involves diverting water from its natural ephemeral stream and conveying it to arable cropping areas.

There are two main methods of diverting and distributing the water.

In one system, the cultivated field close to the stream is first divided into open basins before the water is diverted from the stream into the top most basins by means of a weir.

The water fills the top first basins with the surplus spilling to the next basins and so on until the whole farm is fully wetted.