Introduction. 1 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

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1 Introduction Given the variable nature of rainfall, and the adverse effects that unreliable rainfall can have on crops, farmers have to reduce the risk of having no rainfall at crucial periods of the crop production process. This requires having some form of irrigation to supplement the rainfall. The first requirement of an irrigation system is water, and therefore to have irrigation available to the crop at the appropriate time, the farm has to acquire a reliable water source. This section discusses a number of on-farm mechanisms in-use or being developed for capturing and storing water for use in the irrigation of crops. These options are a supplement to natural rainfall that helps to reduce the water stress and the risk of crop failure due to drought. The chief method is rainwater harvesting, which captures rainwater and stores it for later use on the farm. This section also gives some general details of how useful these systems are, along with a discourse on how surface and sub-surface water resources can also be used as a source of on-farm water. The presentation concludes with a look at water recycling and issues associated with using it as another means of ensuring adequate on-farm water. 1 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

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3 Rainwater Harvesting (RWH) 3 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

4 What is rainwater harvesting (RWH)? Rainwater harvesting (RWH) is the method of capture of rainwater from man-made surfaces (typically roof tops and other constructed surfaces) and its storage for various applications that can include household, agricultural(irrigation and livestock watering), and commercial. For crop production, the risk of water stress and eventual crop failure increases in areas where there are no storage facilities and rainfall is low or unpredictable. In such conditions, rainwater harvesting (RWH) can assist farmers to improve crop productivity and enable them to generate income from their farming activities, in spite of the marginal conditions for agriculture. Important caveats for rainwater harvesting It is important that the system is sized to meet the water demand throughout the dry season if it is to be of significant benefit to farmers. Typically, harvesting systems channel rainwater that falls onto a roof into storage via a system of gutters and pipes. Roof gutters should have sufficient incline to avoid standing water and they must be strong enough to carry peak flows. The storage facility (tank, reservoir, or lined pond) is an important component of the RWH system. The size of the storage facility should be big enough to meet the daily water requirement throughout the dry season. In addition, the size of the catchment area or roof should be large enough to fill the storage. As 4 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

5 much as possible, the storage vessel should be covered to prevent mosquito breeding and to reduce evaporation, contamination and algal growth. Rainwater harvesting systems require regular maintenance and cleaning to keep the system hygienic. Types of rainwater harvesting systems Three types of RWH systems commonly used are: indirectly pumped, directly pumped, and gravity fed. In the indirectly pumped system, rainwater is initially held in a storage tank and then pumped to a header tank. Water is delivered to appliances via gravity. The directly pumped system is a pressurised system. Rainwater is collected and held in a storage tank or reservoir, and then pumped directly to the point of use when required. This is typical of most horticultural irrigation applications. In the gravity fed system, rainwater is collected from the roof, filtered, and fed to a storage (header) tank. Water is delivered to appliances via gravity. Mains which top-up water can also be fitted if needed. The indirectly pumped and gravity fed systems are the ones most commonly used in the Caribbean. 5 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

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7 The advantages and disadvantages of each system are summarised in the table below: 7 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

8 Benefits of rainwater harvesting Rainwater harvesting presents a low-cost approach for mediating dry spell impacts in rain-fed agriculture. The input water is free, so this saves significantly on production costs for the farmer. Therefore RWH can increase profit margins. Moreover many crops respond more favourably to chlorine-free rainwater than they do to treated potable water. The accumulation of chlorine in pipes, pumps, and drippers is also reduced with the use of rainwater, so installed infrastructure can have a longer life. Moreover harvesting rain water can reduce harmful run off into cropped areas, which in turn decreases soil erosion. So RWH has the potential to minimise land degradation, while increasing the water available for productive use. Rainwater harvesting in the Caribbean 8 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

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10 In the Caribbean, RWH continues to be a main source of water supply in many of the drier islands, notably: St. Vincent and the Grenadines, the Leeward and Virgin Islands, and the Bahamas. To further improve the efficiency of RWH systems and to reduce electricity costs, efforts have been made to couple rainfall harvesting with alternative energy. The slide above details an example of Rainwater Harvesting and Solar Power Water Pumping in Jamaica that is operated by the Christiana Potato Growers Cooperative Association and is located in Devon, Manchester in south central Jamaica. 10 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

11 Groundwater Systems 11 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

12 Water wells In areas where rainfall is insufficient to support crops, farmers cannot rely on surface sources of water only. In this case, a number of other options are possible. Chief among them is the use of water wells. A water well is an excavation or structure created in the ground by digging, driving, boring, or drilling to access groundwater in underground aquifers. The water from the well may be drawn up by a number of means including: an electric submersible pump, a trash pump, a vertical turbine pump, a hand pump, or a mechanical pump. It can also be drawn up using containers, such as buckets, that are raised mechanically or by hand. Wells can vary greatly in depth, water volume, and water quality. Well water typically contains more minerals in solution than surface water ( The potential for soil salination is a large risk when choosing the placement of water wells, particularly on island states. Soil salination can occur when wells are sunk on the coast too close to the salt-water lens. This can lead to the intrusion of saline water from the sea into the fresh-water on land. For this reason the site for a well is strictly regulated on all Caribbean islands. Recharging groundwater-infiltration basin (pit) 12 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

13 An infiltration basin (also known as a recharge basin or, in some areas, a sump or pit), is a type of best management practice (BMP) that is used to: manage storm water runoff, prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay. It is, essentially, a shallow artificial pond that is designed to infiltrate storm water though permeable soils into the groundwater aquifer. Farmers dig the infiltration pits along contours. Water collects in the pits during the rainy period. When rainfall is reduced and the soil becomes dry, as in the case of a short period of rain, the water infiltrates underground and is used by the plants. Crops can grow up to maturity by using this conserved moisture. The experience of farmers shows that even if there are only limited days with rain in the whole rainy season, the crops will reach maturity using conserved and harvested water in the pits. This method is widely used in California and Ohio in the United States of America, and also in Algeria, and Egypt in Africa, and Shanghai in China. Its successful application in diverse locations makes it a potentially useful method for the Caribbean, except in countries where the dominant rock type is karsts limestone. In such cases, these basins can increase the likelihood of sinkhole formation. Principles of groundwater extraction and use The potential direct negative environmental impacts of the use of groundwater for irrigation arise from over-extraction (withdrawing water in excess of the recharge rate). This can result in the lowering of the water table, land subsidence, decreased water quality, and saltwater intrusion in coastal areas. Care has to be taken to ensure that 13 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

14 aquifers have sufficient time to recharge, otherwise permanent water stress could develop. But in situations where there are no restrictions on sinking wells and pumping from the same or in cases where enforcement is weak, abuse of groundwater can easily occur. Some innovative approaches have been developed to address this. Rainwater may also be used for ground water recharge where the runoff on the ground is collected and allowed to be absorbed, adding to the groundwater. In other cases sub-surface dykes can be built in an aquifer to obstruct the natural flow of groundwater, thereby raising the groundwater level and increasing the amount of water stored in the aquifer. 14 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

15 Groundwater Systems Case Study: A Successful Case Study of Rainwater Harvesting and Solar Power Water Pumping - Devon, Manchester Jamaica Location This case study was featured as one of the best practice examples in the 2009 report of the United Nations International Strategy for Drought Reduction (UNISDR). In the aftermath of hurricane Ivan in 2004, several islands in the region faced a cessation in production because of the damage that was done to their national grid. In these cases water was available in abundance, but the power to pump the water to required locations was unavailable. At least one farming group in the region managed to couple rainwater harvesting with alternative energy. The Christiana Potato Growers Cooperative Association is located in Devon, Manchester in south central Jamaica. There, rainwater is harvested and pumped by the indirect system using solar energy. How the system works The harvested rainwater from plastic lined ponds drains by gravity into a larger pond at the lowest level on the farm. The water from this pond is then sent to a water storage tank situated at an elevation of 80 feet using a solar-powered pump that is operated on demand. The abundance of sunlight guarantees up to 12 hours of pumping per day, usually between 6am and 6pm. The water from the storage tank then travels through a pipe via gravity to a total of eight high tunnel houses with coverage of 47,000 square feet. The water pressure in the pipe is 30 pounds per square inch, which is more than adequate for the compensation drippers used by the irrigation system. All houses share a common main line to which water is regulated by a hydraulic valve. The valve gets a signal from a timer that sends a 24 volt dc current to open the value for 4 minutes each hour. Economic benefits This has resulted in significant savings in at least three ways. Firstly, due to timed irrigation, water is conserved so that the input cost of water is reduced. Secondly, the amount of potable water used is reduced so that even greater savings are made on water costs. Thirdly, the ability to produce power independent of the national grid saves on costs for electricity. Therefore, this hybrid approach has the potential to increase profits, and allow funding to be channeled into other areas (UNISDR, 2009). 15 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

16 Surface Water Extraction (Rivers and Streams) Trapping surface water The combination of poor watershed management, human population growth, and increased water usage results in limited groundwater storage during rainfall events. This has led to increased stream flows just after rain events and the rapid loss of rainfall water, which would normally be stored in the soil. This has resulted in the trapping of surface water sources by blocking and damming of rivers and streams at various points along their flow. This can be a viable and sustainable small-scale solution to water scarcity since the trapping of water from rivers and streams may not adversely affect the source and the water would otherwise flow to the sea. Surface water use in the Caribbean In the Caribbean, water extraction uses a simple intake structure built at the entry to the irrigation system. Its purpose is to direct water from the original source of supply (river, stream) into the irrigation system. Once the level of the source is above the farm, water travels by gravity to downstream locations fairly efficiently. The water can then be channeled to storage facilities (tanks, reservoirs, ponds) for later distribution to the desired location via canals or pipes. In cases where the river or steam is below the level of the farm, pumping is required to supply the water to the irrigation system. In these cases, it is important to select a large enough pump that gives the correct flow rate to operate the irrigation system. It is also necessary to do routine maintenance to prevent undue build-up of contaminants in the pumps and eventual failure. The siphoning off of water with proper watershed management will not cause undue disturbance to biodiversity and marine life; therefore, this is considered one of the solutions that can be implemented where water sources of sufficient quality and quantity are present. Issues with surface water usage Overuse or abuse of surface water (rivers and streams) could have dire consequences downstream; therefore, where river water extraction is highly practiced by multiple users, there should be monitoring and regulation for optimal results. The advantages and disadvantages of surface water usage are summarised below. 16 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

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19 Water Recycling 19 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

20 Water recycling defined The Water Reuse Association defines reused, recycled, or reclaimed water as water that is used more than one time before it passes back into the natural water cycle. Thus, water recycling is the reuse of treated wastewater for beneficial purposes such as agricultural and landscape irrigation, industrial processes, toilet flushing, or replenishing a groundwater basin. Water reuse allows communities to become less dependent on groundwater and surface water sources, and can decrease the diversion of water from sensitive ecosystems. Additionally, water reuse may reduce the nutrient loads from wastewater discharges into waterways, thereby reducing and preventing pollution. This "new" water source may also be used to replenish overdrawn water sources and rejuvenate or re-establish those previously destroyed. 20 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

21 Reservations with water recycling Care has to be taken when using recycled water, since inadequate treatment before reuse can cause the spread of several water-borne diseases. This risk causes a general apprehension to using recycled water for agricultural production in the Caribbean, largely driven by a fear of contracting a water-borne disease from water initially used for other purposes. Because of this, the use of recycled water for crop irrigation is not very prevalent in the Caribbean. Water recycling in the Caribbean Recycling water from drainage to irrigation canals is practised during times of low water inflows into the irrigation system. In this process, the salt content of the water must first be tested. There are a number of small-scale farm level projects that have attempted to recycle water for crop production. In Jamaica, water fed by drip irrigation to greenhouses is collected at the end of planting beds and re-entered into the water system, provided that the water is not contaminated by pests. In more recent times, farmers have used rainwater that they have harvested to support small freshwater fish sanctuaries, before feeding the nitrogen-rich water to crops. There are at least three benefits that are derived from this: increased nitrogen content reduces the fertiliser input; the farmer has a dual use of harvested water; and, the combination of crop production and aquaculture provides an additional livelihood option. Given strong competition for water in the Caribbean, it is very likely that water recycling will have to be more vigorously pursued in the future. 21 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

22 Summary of On-Farm Water Storage Options for the Caribbean The following is a summary of on-farm water storage options that are of relevance to the Caribbean. In cases where there are no concrete examples of where the options are being used, recommendations are made for likely islands. Summary of Caribbean On-Farm Water Storage Options 22 Module 1.5 Risk Mitigation For Small Holder Agricultural Production In The Caribbean

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