Water Quality of Irrigation Schemes

Irrigation schemes are not even slightly innovative. Shadufs and Archimedean screws dating back to 5,100BP are documented in Ancient Egypt. Qanats existed in the Middle East and North Africa since 600BC. Many other examples populate Africa as well as in Asia and Europe. Onto the 21st Century, 20% of the world’s croplands are irrigated and generate 40% of the global harvest (Khan et al., 2006). As concerns for food security in Africa increase under rapid population growth, irrigation is programmed to seize an increasing share of the water supplies. The continent holds great potential for expansion of irrigated agriculture. However, poorly managed systems are unfortunately common and are associated to waterlogging and pollution, which causes the reduction of productivity (Khan et al., 2006). 

 

                       

Farmer using a shaduf to irrigate fields, picture taken after a painting at tomb of Ipi at Thebes Deir el-Medina, 19th dynasty, c. 1292-1190 BC (Gianni Dagli Orti, 1970)

Generally, water quality considers salinity, sodium hazard, residual sodium carbonates and ion toxicity (Zaman et al., 2018). Salinity occurs in 1.5 million hectares per year globally and is related to rainfall leaching from the soil (Khan et al., 2006). Sodium-related issues emerge with excessive concentrations which reduce the soil’s permeability. Lastly, toxicity may result in stunted growth and early wilting due to obstructed water extraction from the soil matrix. Although water supplies are rarely monitored, institutions adopt specific water quality standards based on different elements. However, such standards may be selected arbitrarily and result inconclusive. Moreover, many assessments focus on the chemical and physical characteristics, overlooking other considerable factors. Singh et al. (2018) developed a new Irrigation Water Quality Index (IWQI) grounded on 12 different parameters attempting eradicate these constraints based on observations from India. Perhaps it is time to look for new, more efficient, indicators. 

 

Soil affected by water salinity (Saline Agriculture Worldwide, n/d)

In large areas of Africa, groundwater has been polluted by arsenic, fluoride, iron or salts making it unsuitable for drinking and further stressing the burdens for water (Van der Hoek et al., 2008). Zaman et al., (2018) proposed a strategy to use salt-polluted waters while maximising freshwater use: freshwater is dedicated to the sensitive young seedlings, while both waters intercalate once the plant becomes established. Occasionally, irrigation canals are the only accessible water resource for domestic uses. Their' water quality was found to be satisfactory for consumption even though quantity of water available for domestic consumption was more important than quality in disease prevention (Van der Hoek et al., 2008). However, quality could gain importance in households lacking storage facilities and toilets. Van der Hoek et al. (2008) observed that decision-makers' prioritise water allocation for agricultural needs over other those of the people, neglecting the users' health. Lastly, a strategy increasingly embraced is water recycling. The first global direct potable reuse plant was commissioned in Windhoek in 1968 (Law, 2003). It exemplifies African innovation and adaptation after groundwater and small-scale dams became redundant in water provision (Laforgue and Lenouvel, 2015). The water reclamation plant originally accommodated 3300m3/day but soon expanded to 7500m3/day. It was followed by the development of the New Goreangab plant in 2002 which in turn treated 21000m3/day, constituting 26% of the produced water in 2003 (Laforgue and Lenouvel, 2015). This project might not have directly influenced the immediate population, given the persistence of informal settlements around the facilities (Gross, 2016). Nevertheless, it has become a reference for projects worldwide and has been quoted in publications by the Australian Water Association (Law, 2003) and the International Conference on Integrated Concepts on Water Recycling (Pisani, 2015). Several new technologies are developing capacities to treat wastewater to be reused for agricultural, industrial and domestic consumption or even as drinking water. Chen et al. (2013) found ‘reclaimed water’ have nutrient, micronutrient and organic properties that benefit the soil. Scepticism regarding the hazardous water components or chemicals have been retracted, proven to be negligible and not a risk factor. All things considered, water recycling needs to follow strict sanitary measures requiring sizeable investment and effort, observing the constraints of the crop and soil types, irrigation methods, cultural norms, and environmental practices.

Goreangab plant in Windhoek, commissioned in 1968 as the first in the world to develop this type of process (Gross, 2016)

Water scarcity limits agricultural development, challenging the sustainability of irrigated agriculture and consequently the food security and livelihoods of producers and consumers (Khan et al., 2006). An increase of 70% in current agricultural productivity is recommended to feed the growing population (Zaman et al., 2018). Therefore, it is imperative to rethink current systems of food production in terms of sustainability and pricing as well as the repartition of water supplies by taking proactive measures. Moreover, landscape capacities must be matched to water supplies in order to manage hazards such as pollution or water logging.