Presentation on theme: "OPEN SESSION IGME: GROUNDWATER AND DROUGHT GROUNDWATER AND AGRICULTURE Ignazio Alba Seville 19/06/2007."— Presentation transcript:
OPEN SESSION IGME: GROUNDWATER AND DROUGHT GROUNDWATER AND AGRICULTURE Ignazio Alba Seville 19/06/2007
BACKGROUND (1/3) Agriculture is the sector with the highest worldwide demand for water, and at the same time it is the sector with the highest losses and waste of water. In the Southern and Eastern parts of the Mediterranean region, for example, irrigation in agriculture consumes about 80% of the withdrawn water resources. In arid and semi-arid areas, the availability of adequate amount of water is the most significant single factor limiting crop production. This factor must therefore receive high attention.
BACKGROUND (2/3) Owing to the increasing demand for domestic and industrial uses, the amount of fresh water allocated to irrigation will be significantly reduced in the future. Consequently, on one hand irrigation is affected by the scarcity of water, and on the other hand it is responsible for the misuse of water. In arid and semi-arid zones where surface water alternatives are not available, groundwater is under pressure from competing uses. During the last decades in many countries groundwater has become an important source of water for irrigation use. It is estimated that about 30% of the worlds irrigation supply originates from groundwater (FAO, 2003).
BACKGROUND (3/3) If agriculture production and living standards are to be maintained, greater priority must be given to a proper water resources management and to enhance the efficiency of water collection and utilization. Increasing water use efficiency (WUE) in dry areas becomes a vital and crucial issue. Indeed, as stated during the World Water Forum of Kyoto, one must produce more out of less water or more crop per drop.
GROUNDWATER IN AGRICULTURE As the subject is very large, I would like to draw your attention on some practical examples and experiences gained in the framework of the International Co-operation for Developing Countries. In particular, the experiences of groundwater utilization for irrigation purpose, wich will be presented include exploiting shallow water table, deep unconfined and confined aquifers and fossil water or paleo water.
GROUNDWATER IN AGRICULTURE (Sudan) Small farmers withdraw groundwater from dug wells (usually constructed when the water table is shallow) for domestic and irrigation uses. This practice is common in many developing countries. Old type wells in North-west Darfur (Sudan).
GROUNDWATER IN AGRICULTURE (Senegal) Dug wells, utilised to irrigate small plots of vegetables.
GROUNDWATER IN AGRICULTURE (1/4) (Tunisia) In the South-east Tunisia groundwater represents the main source of water supply. This is an example of a deep drilled well utilised for irrigation purposes. Well Depth: 483 m; Static level: -33m Flow: 45 l/sec Salinity: 5 dS/m Irrigated area: 65 ha. Irrigation methods: basin, furrow and microirrigation.
GROUNDWATER IN AGRICULTURE (2/4) (Tunisia) In some farms water is accumulated in a pond to supply microirrigation systems.
GROUNDWATER IN AGRICULTURE (3/4) (Tunisia) This is an example of groundwater exploitation by a drilled well in the medium aquifer Complexe Terminal, for irrigation of date palms (south- western part of Tunisia). Flow: 60 l/sec Salinity: ECw=2.8-2.9 dS/m Date palms plot Drilled well and tank
GROUNDWATER IN AGRICULTURE (4/4) (Tunisia) The main problem in this area is the great waste of fossil water due to the irrigation methods with the risk of water logging and soil salinization.
GROUNDWATER IN AGRICULTURE (1/4) (Lybia) In Libya, surface water resources are rather limited and contribute to less than 3% of the total water use for the different activities. Groundwater represents the main source of water supply. It is exploited through wells ranging from few meters to more than 1000 m in depth. Groundwater aquifers are either renewable or non-renewable.
GROUNDWATER IN AGRICULTURE (2/4) (Lybia) Recently, several well fields were developed (in Kufra area) to supply the Great Man made River Project (GMRP). When completed, the GMRP will supply more than 6 Mm3/day to the agricultural fields and urban areas in the north.
GROUNDWATER IN AGRICULTURE (3/4) (Lybia) The Kufra basin covers an area of over 200 000 km 2 and consists of a deep Paleozoic aquifer and a more widely used upper aquifer known as the Nubian Sandstone. Production wells drilled for agricultural water supply range in depth from 400 to 500 m with productivity ranging from 100 to 300 m3 /hr and a water quality between 180 and 300 mg/l of TDS. The Sarir Basin located to the north of Kufra basin and covers a surface area of more than 450 000 km 2 and consists of a number of aquifers belonging to the Post-Eocene. Depth of wells tapping these aquifers range from 400 to 500 m with productivity varying from 150 to 300 m3/hr and water quality in the order of 1200 mg/l.
GROUNDWATER IN AGRICULTURE (4/4) (Lybia) The water is carried out through two pipes, 4 m of diameter, and accumulated in a reservoir constructed in Sirte area. Reservoir in Sirte area.
GROUNDWATER IN AGRICULTURE (1/6) (Egypt) Siwa oasis is located at a distance of 300 Km south-west of Marsa Matrouh and 65 Km from the Egyptian-Libyan border, in a depression of the Western Desert of Egypt. In Siwa Oasis no significant surface water exists. All water in the oasis is considered to be part of groundwater.
GROUNDWATER IN AGRICULTURE (2/6) (Egypt) Beside the natural springs (more than 200) the source of groundwater is from three aquifers: the upper limestone aquifer (shallow, 15-95 m deep), the lower limestone aquifer (70-130 m) the Nubian Sandstone aquifer (900-1050 m below ground surface).
GROUNDWATER IN AGRICULTURE (3/6) (Egypt) The water salinity range from 200-500 ppm (Nubian sandstone) to 1500-8000 ppm and in some wells up to 32.000 ppm. In some cases, fresh water and saline water are accumulated in two different reservoirs for blending, in order to lower the salinity level. Part of fresh water is bottled.
GROUNDWATER IN AGRICULTURE (5/6) (Egypt)) There are two main problems facing the people and farmers in Siwa: The drainage problem because there is no outlet to allow water to drain outside-the basin and the up-raise of the water level in the area due to the water accumulation with the water logging risk. Increase of soils salinity.
GROUNDWATER IN AGRICULTURE (6/6) (Egypt) Results of Salinity and Water logging impacts.
GROUNDWATER IN AGRICULTURE (1/3) (Sicily) In Sicily, in some areas (Licata area, as an example) surface waters have a high level of salinity and then the only alternative is groundwater that unfortunately is brackish as well (although less than surface water). Investigation area Salso river
GROUNDWATER IN AGRICULTURE (2/3) (Sicily) The withdrawal of groundwater is made through dug wells with large mouth - roman type - with a diameter 4-6 m and deep 10-12 m and drilled wells deep 60-70 m. Flow 0.5-3.0 l/sec. Salinity: ECw = 3.9 – 5.3 dS/m
GROUNDWATER IN AGRICULTURE (3/3) (Sicily) Main problems of the area: salinity of groundwater range from 2 dS/m to 14 dS/m; in the coastal zone, the over exploitation of water table determines the intrusion of sea water by making worse the situation; The use of brackish water has determined the accumulation of salts in the soils originally non salines; the value of E.C.e. has increased from 0.2-0.3 dS/m to 4.6-14.6 dS/m (Raimondi S. et al 2001).
INTERACTION GROUNDWATER-AGRICULTURE There are a large variety of threats that agriculture can pose to groundwater and vice-versa: Threats to Groundwater Threats to Agriculture
Threats to Groundwater Threats to the quantity : Overdraft, Drawdown, Subsidence. Threats to quality : The over exploitation of water table in coastal zones is responsible of the intrusion of sea water and then of the water table salinisation. Inorganic compounds, pathogens and organic compounds can harm water quality, affecting the health of humans, fish and wildlife.
Threats to Agriculture The use of saline groundwater for irrigation determine the accumulation of salts in soils originally non-salines (secondary salinisation); Salinisation of soils becomes then one of the main risk factors of desertification. The up-raise of the water table determines the waterlogging risk.
ACTIONS TO MITIGATE IMPACTS IN AGRICULTURE (1/6) Introduction of more efficient irrigation techniques (e.g. micro- irrigation) in order to save water, by providing the best possible conditions of total soil water potential by using saline waters and by avoiding leaf injury. The only problem with this method is the need to remove salts that accumulate at the wetting front (Shalhevet, 1994).
ACTIONS TO MITIGATE IMPACTS IN AGRICULTURE (2/6) Rain water harvesting from roof-top of greenhouses and farmhouses.
ACTIONS TO MITIGATE IMPACTS IN AGRICULTURE (3/6) Costruction of small ponds utilised to accumulate the water harvested during the winter period. Moreover, they are utilised to blend fresh water with brackish water in order to lower the salinity level.
ACTIONS TO MITIGATE IMPACTS IN AGRICULTURE (4/6) Coping with drought AT FARM LEVEL through: Deepening of existing wells; Construction of new wells; Water transfer by trucks (in extreme cases and for small farms)
ACTIONS TO MITIGATE IMPACTS IN AGRICULTURE (5/6) Adoption of flexible irrigation scheduling minimizing water loss (evaporation reduction by mulching or rapid crop cover, minimum tillage, weeding, windbreak, etc.)
ACTIONS TO MITIGATE IMPACTS IN AGRICULTURE (6/6) Strengthening capacity building of technicians and farmers through Training Course in Water and Irrigation Management: Theory and Practice.
CONCLUSIVE REMARKS (1/2) Groundwater has a very important role for irrigated agriculture in particular where there is scarcity of surface waters and during drought periods; In all examples presented the prevailing problem of groundwater is related to water salinity; In irrigated agriculture, supplied principally by groundwater and in arid zones, particular attention must be paid to the management of saline water (in order to avoid the risk of soil salinisation and water logging) since the natural leaching of salts by rainfall often does not occurs and there is scarcity of fresh water.
CONCLUSIVE REMARKS (2/2) A proper management of non-renewable groundwater (often transboundary) is recommeded in order to take into account the sustainability of this resource; Farmers must utilize the best cultural practices to avoid the pollution of groundwater; Use of groundwater can be considered as a strategic reserve during drought periods, in particular, where the surface water is the main resource.