Integration of 1401 Graduate Studies (Groundwater Management for Sustainable Farming Systems)

This report presents the integration of research studies carried out by the graduate students at UTS and UNSW as part of the CRC for Sustainable Rice Production Graduate Studies Program. It evaluates the methodologies and modelling scenarios in rice-based irrigation areas. Moreover, the report collates the research findings and conclusions to establish the benefits to rice industry. The main objective of the graduate studies was to develop strategies for managing groundwater for salinity mitigation at farm and regional scale. Through field experimentation and modelling approaches, the studies examined the impacts of land use on the environment and the effect of irrigation water with different quality levels on the rising watertable and the subsequent salinisation. These studies developed hydrogeological information base for rice growing areas mainly MIA (Murrumbidgee Irrigation Area) and WID (Wakool Irrigation District) has been developed that includes monitoring groundwater levels, groundwater quality, soil analysis and geophysical surveys. The modelling exercises show strong interaction between shallow and deep aquifer. The simulations show significant rise in groundwater levels during the rice crop season and fall during the fallow season. Subsurface lateral groundwater flows are dominant from east to west; from Narrandera to Hay. Groundwater monitoring indicated a rapid response to rainfall as well as irrigation events with a recharge estimation of about 80% for the shallow aquifer and 50% for the deep aquifer. The shallow aquifer (2 m) responds slightly faster than the deep aquifer (7 m) to irrigation events. Groundwater quality at Whitton (M.I.A) is classified as brine and therefore not suitable for irrigation. However, the irrigation water was classified as fresh. Sodium, Sulfate and Chloride were the most abundant elements found in the four water samples. The piezometers in irrigated paddocks showed substantially lower salinity indicating that irrigation water was recharging the aquifer. The deep aquifer piezometers monitoring displayed conductivity values of about 5 to 6 ms/cm. The geophysical resistivity imaging has shown a great promise for developing understanding about surface-ground water interactions and salinization. Large spatial variations in apparent resistivity were observed in irrigated and non-irrigated areas. Resistivity decreases with depth in a linear fashion. Variations in resistivity have been noticed in the upper 10 metre layer of soil indicating recharge zone. Increase of resistivity closer to rice paddocks during irrigation is due to the fresh water infiltrating to the aquifer. Irrigation events resulted in decreased resistivity at most depths, particularly at 15 m that reflecting rising water table or input of fresh water from the irrigated paddocks. These studies have shown a strong correlation between resistivity and electromagnetic responses from EM31 and EM34. The MODFLOW model developed by the UTS graduates with a 10 m minimum discretisation and a refined time scale (2 days stress period) simulated the groundwater dynamics with 80% accuracy. Six key parameters are identified influencing the system. They include rice ponding, precipitation, drainage, evapotranspiration deep leakage and lateral groundwater flow. The solute transport model revealed that the groundwater salinity is controlled by rising groundwater levels due to rice ponding. Salinity concentration is higher in top 2 metres below -2- ground surface. The solute transport model has successfully simulated salinity trends. The irrigated areas are affected by irrigation water salinity. The salinity of top 3 m profile is higher and decreases with depth. Groundwater salinity ranges from 1500 mg/l directly below and is approximately 2500 – 3000 mg/l in the fallow paddocks adjacent to the rice pond. According to the optimization results, an extensive bore network of several hundred pumping bores at shallow depths would be necessary to lower water levels around the irrigated area. However, it impossible to pump out the necessary groundwater volumes in order to lower water table to the targeted levels in low permeability areas as vertical hydraulic conductivity is one order of magnitude lower than horizontal hydraulic conductivity. The UNSW PhD (Xu, 2003) study in Wakool region predicted that about 2 kg/m2 salt will be added to root zone per one rice crop per season. This prediction quantifies to 20 t/ha per crop season each year. Moreover, if repeated irrigation with saline water is practiced, the salt concentration in root zone will continue to increase with time, which is alarming for future of rice industry. Therefore, careful decisions need to be done while working out the soil suitability for rice growers regarding existing soil salinity and the EC levels in irrigation water. The ponded rice irrigation is a major contributing factor to groundwater accessions resulting in rising watertables and subsequent salinity problem. The alternative use of fresh and low salinity water could be practiced on short-term basis for ponded irrigation as long as it does not affect rice growth or rice yield. This will help remove accumulated salts in the root zone by fresh water irrigation after the irrigation with water containing salts. The six graduate modelling studies described in this report are site specific. Efforts to apply these methods to other farms or regions will need to incorporate site specific information on cropping, topography and groundwater systems to describe and calibrate the salinisation processes

from solute recycling concepts to quantitative risk assessment

The main objective of this thesis is the quantitative investigation of groundwater salinisation induced by solute recycling from irrigation, and its implications for the overall salinisation in coastal settings. Since the modelling approaches proposed in literature to simulate seawater-intruded areas rarely account for the coupled and superimposed effects of solute recycling and seawater intrusion, simulation procedures have been developed, to evaluate the impact of salinisation induced by ...thesi

An approach to valuing ponds within farming systems for aquaculture

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Sustainability of irrigated agriculture under salinity pressure – A study in semiarid Tunisia

In semiarid and arid Tunisia, water quality and agricultural practices are the major contributing factors to the degradation of soil resources threatening the sustainability of irrigation systems and agricultural productivity. Nowadays, about 50% of the total irrigated areas in Tunisia are considered at high risk for salinization. The aim of this thesis was to study soil management and salinity relationships in order to assure sustainable irrigated agriculture in areas under salinity pressure. To prevent further soil degradation, farmers and rural development officers need guidance and better tools for the measurement, prediction, and monitoring of soil salinity at different observation scales, and associated agronomical strategy. Field experiments were performed in semi-arid Nabeul (sandy soil), semi-arid Kalâat Landalous (clay soil), and the desertic Fatnassa oasis (gypsiferous soil). The longest observation period represented 17 years. Besides field studies, laboratory experiments were used to develop accurate soil salinity measurements and prediction techniques. In saline gypsiferous soil, the WET sensor can give similar accuracy of soil salinity as the TDR if calibrated values of the soil parameters are used instead of standard values. At the Fatnassa oasis scale, the predicted values of ECe and depth of shallow groundwater Dgw using electromagnetic induction EM-38 were found to be in agreement with observed values with acceptable accuracy. At Kalâat Landalous (1400 ha), the applicability of artificial neural network (ANN) models for predicting the spatial soil salinity (ECe) was found to be better than multivariate linear regression (MLR) models. In semi-arid and desertic Tunisia, irrigation and drainage reduce soil salinity and dilute the shallow groundwater. However, the ECgw has a larger impact than soil salinity variation on salt balance. Based on the findings related to variation in the spatial and temporal soil and groundwater properties, soil salinization factors were identified and the level of soil “salinization risk unit” (SRU) was developed. The groundwater properties, especially the Dgw, could be considered as the main cause of soil salinization risk in arid Tunisia. However, under an efficient drainage network and water management, the soil salinization could be considered as a reversible process. The SRU mapping can be used by both land planners and farmers to make appropriate decisions related to crop production and soil and water management

The hydrosalinity module of ACRU agrohydrological modelling system (ACRUsalinity) : module development and evaluation.

Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.Water is characterised by both its quantity (availability) and its quality. Salinity, which is one of the major water quality parameters limiting use of a wide range of land and water resources, refers to the total dissolved solutes in water. It is influenced by a combination of several soil-water-salt-plant related processes. In order to develop optimum management schemes for environmental control through relevant hydrological modelling techniques, it is important to identify and understand these processes affecting salinity. Therefore, the various sources and processes controlling salt release and transport from the soil surface through the root zone to groundwater and streams as well as reservoirs are extensively reviewed in this project with subsequent exploration of some hydro salinity modelling approaches. The simulation of large and complex hydrological systems, such as these at a catchment scale, requires a flexible and efficient modelling tool to assist in the assessment of the impact of land and water use alternatives on the salt balance. The currently available catchment models offer varying degrees of suitability with respect to modelling hydrological problems, dependent on the model structure and the type of the approach used. The A CR U agrohydrological modelling system, with its physically-conceptually based characteristics as well as being a multi-purpose model that is able to operate both as a lumped and distributed model, was found to be suitable for hydro salinity modelling at a catchment scale through the incorporation of an appropriate hydro salinity module. The main aim of this project was to develop, validate and verify a hydro salinity module for the ACRU model. This module is developed in the object-oriented version of ACRU, viz. ACRU2000, and it inherits the basic structure and objects of the model. The module involves the interaction of the hydrological processes represented in ACRU and salinity related processes. Hence, it is designated as ACRUSalinity. In general, the module is developed through extensive review of ACRU and hydrosalinity models, followed by conceptualisation and design of objects in the module. It is then written in Java object-oriented programming language. The development of ACRUSalinity is based mainly on the interaction between three objects, viz. Components, Data and Processes. Component objects in ACRU2000 represent the physical features in the hydrological system being modelled. Data objects are mainly used to store data or information. The Process objects describe processes that can take place in a conceptual or real world hydrological system. The Process objects in ACRUSalinity are grouped into six packages that conduct: • the initial salt load determination in subsurface components and a reservoir • determination of wet atmospheric deposition and salt input from irrigation water • subsurface salt balance, salt generation and salt movement • surface flow salt balance and salt movement • reservoir salt budgeting and salt routing and • channel-reach salt balancing and, in the case of distributed hydro salinity modelling, salt transfer between sub-catchments. The second aim of the project was the validation and verification of the module. Code validation was undertaken through mass balance computations while verification of the module was through comparison of simulated streamflow salinity against observed values as recorded at gauging weir UIH005 which drains the Upper Mkomazi Catchment in KwaZuluNatal, South Africa. Results from a graphical and statistical analysis of observed and simulated values have shown that the simulated streamflow salinity values mimic the observed values remarkably well. As part of the module development and validation, sensitivity analysis of the major input parameters of ACRUSalinity was also conducted. This is then followed by a case study that demonstrates some potential applications of the module. In general, results from the module evaluation have indicated that ACRUSalinity can be used to provide a reasonable first order approximation in various hydrosalinity studies. Most of the major sources and controlling factors of salinity are accommodated in the ACRUSalinity module which was developed in this project. However, for a more accurate and a better performance of the module in diversified catchments, further research needs to be conducted to account for the impact of salt loading from certain sources and to derive the value of some input parameters to the new module. The research needs include incorporation in the module of the impact of salt loading from fertilizer applications as well as from urban and industrial effluents. Similarly, further research needs to be undertaken to facilitate the module's conducting salt routing at sub-daily time step and to account for the impact of bypass flows in heavy soils on the surface and subsurface salt balances

Researching Solutions to the Sustainability and Environmental Challenges for Rice-based Cropping Systems in Southern Australia

The major threat to the sustainability of irrigated agriculture in the rice growing regions of the southern Australia is secondary salinisation as a result of rising watertables. Rice growing contributes about half of the accessions to the groundwater in these regions. A range of strategies for reducing the accessions from rice are applied, including restricting rice growing to soil assessed as suitable for rice. In the past this was based on soil texture, but increasingly EM-31 survey is being used, and the inclusion of soil sodicity constraints will further improve the ability to predict suitable soils. The net evaporative demand for rice growing over the whole season is well-approximated by reference evapotranspiration (ETo), which is used to calculate the seasonal rice paddock water use limit. Potential methods for increasing rice water use efficiency and reducing recharge include shorter duration varieties and a range of water and soil management strategies. Intermittent and sprinkler irrigation can significantly reduce water use, however yields are also reduced due to cold temperature damage during early pollen microspore. Small areas of leaky soils can greatly increase total accessions to the watertable, and EM-31 surveys show that many “suitable” rice paddocks have leaky areas. Recharge from leaky areas can be reduced by puddling or by impact compaction. After rice harvest, soil water content is high, and recharge may continue, especially under the influence of winter rainfall and low evaporation. Research is underway to quantify the effect on accessions to the watertable of growing a winter crop immediately after rice harvest. Future work will investigate the conjunctive use of groundwater and surface water to promote watertable control while maximising agricultural productivity by making more water available for irrigation. The SWAGMAN (Salt Water And Groundwater MANagement) series of computer models has been developed to determine the impacts of management and climate on watertables, salinisation and yield, and the tradeoffs between environmental objectives and profitability. These models include SWAGMAN Destiny, a point scale crop model that can be run for up to 30 years of climatic data. SWAGMAN Farm is a farm scale optimisation model which predicts the most economic cropping mixes that meet specified net recharge and root zone salinity objectives, taking into account farmer preferences. Regional groundwater models have been developed to evaluate the impacts of climate and management on watertables. The development of shallow saline watertables results in the generation of saline drainage waters. Numerous evaporation basins ranging in size from a couple of hectares to a few hundred hectares have been created in recent years to receive saline drainage. Investigations into the salt and water balance of evaporation basins, the development of the model BASINMAN, and economic analyses have led to guidelines for the siting, design and management of evaporation basins. A pilot trial is also underway to investigate the feasibility of serial biological concentration, with the production of high value crops in the first 2 stages, followed by salt tolerant crops (stage 3), fish farming (4), evaporation basins (5) and a solar pond to generate energy

Research Solutions To Watertable And Salinity Problems In The Rice Growing Areas Of Southern Australia

The major threat to the sustainability of irrigated agriculture in the rice growing regions of the southern Australia is secondary salinisation as a result of rising watertables. Rice growing contributes about half of the accessions to the groundwater in these regions. A range of strategies for reducing the accessions from rice are applied, including restricting rice growing to soil assessed as suitable for rice. In the past this was based on soil texture, but increasingly EM- 31 survey is being used, and the inclusion of soil sodicity constraints will further improve the ability to predict suitable soils. The net evaporative demand for rice growing over the whole season is well-approximated by reference evapotranspiration (ETo), which is used to calculate the seasonal rice paddock water use limit. Potential methods for increasing rice water use efficiency and reducing recharge include shorter duration varieties and a range of water and soil management strategies. Intermittent and sprinkler irrigation can significantly reduce water use, however yields are also reduced due to cold temperature damage during early pollen microspore. Small areas of leaky soils can greatly increase total accessions to the watertable, and EM-31 surveys show that many “suitable” rice paddocks have leaky areas. Recharge from leaky areas can be reduced by puddling or by impact compaction. After rice harvest, soil water content is high, and recharge may continue, especially under the influence of winter rainfall and low evaporation. Research is underway to quantify the effect on accessions to the watertable of growing a winter crop immediately after rice harvest. Future work will investigate the conjunctive use of groundwater and surface water to promote watertable control while maximising agricultural productivity by making more water available for irrigation. The SWAGMAN (Salt Water And Groundwater MANagement) series of computer models has been developed to determine the impacts of management and climate on watertables, salinisation and yield, and the tradeoffs between environmental objectives and profitability. These models include SWAGMAN Destiny, a point scale crop model that can be run for up to 30 years of climatic data. SWAGMAN Farm is a farm scale optimisation model which predicts the most economic cropping mixes that meet specified net recharge and root zone salinity objectives, taking into account farmer preferences. Regional groundwater models have been developed to evaluate the impacts of climate and management on watertables. The development of shallow saline watertables results in the generation of saline drainage waters. Numerous evaporation basins ranging in size from a couple of hectares to a few hundred hectares have been created in recent years to receive saline drainage. Investigations into the salt and water balance of evaporation basins, the development of the model BASINMAN, and economic analyses have led to guidelines for the siting, design and management of evaporation basins. A pilot trial is also underway to investigate the feasibility of serial biological concentration, with the production of high value crops in the first 2 stages, followed by salt tolerant crops (stage 3), fish farming (4), evaporation basins (5) and a solar pond to generate energy

Risk based approach for managing salt accumulation in soil irrigated with recycled water

Recycling is one of the viable options to attain sustainable management of wastewater. The supply and reuse of recycled water may play an important role in enhancing urban water supplies in many water-scarce parts of industrialised countries because of its reduced treatment cost relative to seawater desalination and imported surface water. One such reuse option includes application of recycled water for irrigating urban open fields. Past literature suggests that the continuous use of recycled water over a long period of time may lead to the accumulation of salt in the root zone. Salt transport models to quantify salt accumulation in soil exist, but these do not consider the stochastic nature of the elements of salt accumulation process. Moreover, none of the past studies propose a framework to manage and control the salt accumulation process due to recycled water irrigation by considering stochastic nature of different components. The study described in the thesis details a novel methodology adopted for the development and implementation of an integrated risk based approach to control sources of salinity and the level of treatment required to use recycled water in irrigation in a sustainable manner. The study included laboratory and field work and involved thorough investigation of site specific soil, data analysis, development of relationships among elements of salt accumulation process, and incorporated long-term prediction modelling result and scientific knowledge into a framework. One of the key investigations conducted was to understand and monitor salt accumulation process in columns using sensors in terms of depth of soil, type of soil and type of irrigation water. Data generated from these experiments and output from simulation were used to develop the framework. Therefore, the overall aim of this study was to develop a framework with the help of a probabilistic method, namely, Bayesian belief network (BBN) to manage the salinity in the root zone due to recycled water irrigation. Results from the column study show that due to recycled water irrigation, soil water electrical conductivity (ECSW) was higher in the upper part of the column (0-0.2 m) than the lower part. This is because only applied irrigation water could not leach the salt from upper part to downward. When simulated rainfall was applied (once in a week) in a loamy sand column along with recycled water (twice in a week), the average ECSW showed a decreasing pattern with time. In another column study with silty loam soil, average sodium adsorption ratio due to recycled water (EC = 0.8 dS/m) irrigation was 3.6 times more than the tap water (EC = 0.2 dS/m) irrigation and 1.4 times less than the synthetic saline water (EC = 2.0 dS/m) irrigation. In the same column study, it was observed that the ratio of soluble cations (Na+: Mg2+: Ca2+: K+) in the soil sample changed than its initial ratio at the beginning of the study. The change in the ration occurred because of exchanging cations between soil and the water added for irrigation. A salt transport model HYDRUS 1D was validated with experimental results and used to predict risk of salt accumulation in field condition. The salt transport modelling carried out in this study shows that in drought condition, yearly averages ECSW exceeded the maximum salinity tolerance threshold of 5.0 dS/m for rye pasture due to recycled water irrigation in a loamy sand paddock. The ECSW exceeded 1, 59, 79, 87 and 90% for the years from 1 to 5, respectively. In another modelling with future climate condition between years 2021 and 2040 shows that ECSW was 24% higher in loamy soil paddock compared to loamy sand paddock. Amount of leachate in the loamy sand paddock was 27% more than the amount leached from loamy paddock, which may pose a salinity risk to the ground water if there is a perched aquifer in the field at a depth < 1 m. BBN framework analyses identified that for root zone ECSW of 2.25 dS/m, it is 92% probable that the Na+ concentration of the root zone soil water would be in the range of 5 – 15 mmol(c)/L; for ECSW of 16.5 dS/m, there is 86% probability that the Na+ concentration of root zone soil water would be in the range of 30 – 35 mmol(c)/L. Furthermore, over the study period of 2021 to 2040, it was found that the reduction of the posterior mean of recycled water EC by 13% (from μ=0.92 to μ=0.8 dS/m), brings the average root zone ECSW down from 6.5 dS/m to 4 dS/m, which is within the salinity threshold limit for rye pasture. The BBN framework also identified the most significant sources of salinity contributing to wastewater and proposed control strategy of those sources to minimise the salt accumulation in the soil for a sandy loam oval irrigated with recycled water. Results show that accumulation of salt in the root zone was largely due to the salt load in the wastewater stream from washing machines and the salt load in the wastewater from toilets was the second most influential source. It was found that by controlling multiple sources at the same time significantly reduces salt accumulation in the soil. It was observed that by using environmental friendly detergents reduce the TDS load in the laundry stream by 4 to 7 times and Na+ load by 2 times than popular brand detergents. Irrigation scheduling with recycled water is typically done while considering only the soil moisture levels. The study reported in this thesis proposes that besides considering the soil moisture levels, salt accumulation within the soil must be considered while irrigating open fields using recycled water. Proposed methods and outcome of this research would provide vital knowledge about the uncertainty associated with root zone salinisation of urban open fields, and better management and control of root zone salinity due to irrigation with recycled water. The study highlighted that any strategies that help in the reduction of salt in the recycled water will be beneficial in managing the soil salinity as a result of recycled water use for irrigating open fields. Hence, the proposed decision making tool for controlling the risk of soil salinisation can assist in developing recycled water irrigation schemes which are sustainable over the long-run

Containing salinity through irrigation management: the case of the Fordwah area in Pakistan

International audienceLa salinité des sols a toujours été une contrainte de l'agriculture irriguée dans le bassin de l'indus. Traditionnellement, ce phénomène était associé à la remontée d'une nappe, devenue sub-affleurante à certains endroits, avec l'introduction des périmètres irrigués à grande échelle. Le concept de la «menace jumelle» de l'engorgement et de la salinité des sols a impulsé depuis les années 1960 un grand nombre de projets de drainage à grande échelle pour rabattre la nappe. Par ailleurs, pour faire face aux pénuries d'eau, les agriculteurs ont recouru à des pompages individuels dans la nappe dont le niveau a ainsi baissé. Le nombre de forages est estimé à plus de 500 000 et continue d'augmenter. L'utilisation des eaux souterraines, souvent d'une qualité médiocre mais hétérogène dans l'espace, accentue une tendance à la salinisation des sols. L'eau de surface, en revanche, est d'excellente qualité et représente une valeur inestimable pour les paysans ayant des problèmes de salinité et sodicité. Une distribution de l'eau de surface en phase avec les contraintes des paysans en termes de qualité de l'eau de nappe pourrait contribuer à diminuer ces problèmes. (Résumé d'auteur