The Arizona Water Settlement Act and urban water supplies

The 2004 Arizona Water Settlements Act (AWSA 2004) when implemented will allocate to two Native American tribes, the Gila River Indian Community (GRIC) and the Tohono O’odham Nation (TON) almost ten percent of Arizona’s total developed water supply, which is 7.04 million acre-feet a year. The successful passage of AWSA, given the scale of the water rights settlement and competing uses for finite water supplies, is the topic of this paper. Key motivations for the settlement are that: (1) the 653,500 acre-feet a year allocation is around a third of the GRIC’s Gila River Adjudication 2001 claim; (2) the GRIC signed a number of water leases and exchanges providing water to municipalities and has not ruled out signing more; and (3) AWSA resolved more than tribal water claims; it also settled thorny issues of Central Arizona Project (CAP) debt repayment (for $2 billion in construction costs) and division of water allocation between federal (Indian) and state (non-Indian) uses including the reallocation of high priority uncontracted CAP water to cities.     

Assessing water stress in a hedgerow olive orchard from sap flow and trunk diameter measurements

We used sap flow and trunk diameter measurements for assessing water stress in a high-density ‘Arbequina’ olive orchard with control trees irrigated to replace 100 % of the crop water needs, and 60RDI and 30RDI trees, in which irrigation replaced ca. 60 and 30 % of the control, respectively. We calculated the daily difference for both tree water consumption ( $ D_{{E_{\text{p}} }} $ ) and maximum trunk diameter (D _MXTD) between RDI trees and control trees. The seasonal dynamics of $ D_{{E_{\text{p}} }} $ agreed reasonably well with that of the stem water potential. We identified peculiarities on the response $ D_{{E_{\text{p}} }} $ to changes in water stressing conditions, which must be taken into account when using the index. An analysis of the water stress variability in the orchard is required for choosing the instrumented trees. The reliability of the D _MXTD index was poorer than that of $ D_{{E_{\text{p}} }} $ . The maximum daily shrinkage (MDS) was not a reliable water stress indicator.     

Calibration and validation of a remote sensing algorithm to estimate energy balance components and daily actual evapotranspiration over a drip-irrigated Merlot vineyard

A study was carried out to calibrate and validate a remote sensing algorithm (RSA) for estimating instantaneous surface energy balance components and daily actual evapotranspiration (ETa) over a drip-irrigated Merlot vineyard located in the Maule Region of Chile (35° 25′ LS; 71° 32′ LW; 125?m.a.s.l.). ETa was estimated as a function of instantaneous evaporative fraction and average daily net radiation (Rn_day) using meteorological variables in combination with reflectance data measured by a hand-held multi-spectral radiometer. The sub-models used to estimate the instantaneous net radiation (Rn_ins), soil heat flux (G _ins), and Rn_day were calibrated and validated using measurements of the surface energy balance components, incoming longwave radiation $(L \downarrow_{\text{ins}})$ , outgoing longwave radiation $(L \uparrow_{\text{ins}})$ , and surface albedo (α). The validations of instantaneous sensible heat flux (H _ins), latent heat flux (LE_ins), and ETa were carried out using turbulent energy fluxes obtained from an eddy correlation (EC) system. For reducing the moderate EC imbalance (about 11?%), turbulent energy fluxes were recalculated using the Bowen ratio method. The validation analysis indicated that the calibrated sub-models of the RSA were able to estimate Rn_ins, G _ins, H _ins, and LE_ins with a root-mean-square error (RMSE), mean absolute error (MAE), and index of agreement (IA) ranging between 16–54, 13–44?W?m^?2, and 0.72–94, respectively. Also, the RSA was able to estimate ETa with RMSE?=?0.38?mm?day^?1, MAE?=?0.32?mm?day^?1 and IA?=?0.96. These results demonstrate the potential use of reflectance and meteorological data to estimate ETa of a drip-irrigated Merlot vineyard.     

Surface energy balance model of transpiration from variable canopy cover and evaporation from residue-covered or bare soil systems: model evaluation

A surface energy balance model (SEB) was extended by Lagos et al. Irrig Sci 28:51–64 (2009) to estimate evapotranspiration (ET) from variable canopy cover and evaporation from residue-covered or bare soil systems. The model estimates latent, sensible, and soil heat fluxes and provides a method to partition evapotranspiration into soil/residue evaporation and plant transpiration. The objective of this work was to perform a sensitivity analysis of model parameters and evaluate the performance of the proposed model to estimate ET during the growing and non-growing season of maize (Zea Mays L.) and soybeans (Glycine max) in eastern Nebraska. Results were compared with measured data from three eddy covariance systems under irrigated and rain-fed conditions. Sensitivity analysis of model parameters showed that simulated ET was most sensitive to changes in surface canopy resistance, soil surface resistance, and residue surface resistance. Comparison between hourly estimated ET and measurements made in soybean and maize fields provided support for the validity of the surface energy balance model. For growing season’s estimates, Nash–Sutcliffe coefficients ranged from 0.81 to 0.92 and the root mean square error (RMSE) varied from 33.0 to 48.3 W m^?2. After canopy closure (i.e., after leaf area index (LAI = 4) until harvest), Nash–Sutcliffe coefficients ranged from 0.86 to 0.95 and RMSE varied from 22.6 to 40.5 W m^?2. Performance prior to canopy closure was less accurate. Overall, the evaluation of the SEB model during this study was satisfactory.     

Analytical formulae for traverse drainage of sloping lands with constant rainfall

To solve the problem of traverse drainage of sloping lands, the author extends continuity and motion equations to vertically heterogeneous soils and shows that the steady-state solution combines two asymptotic curves (gentle and steep slopes) and can be reduced to simple analytical equations, clearly revealing the influence of the slope; Boussinesq's first approximation (flow parallel to the impervious layer) should be used, rather than his second approximation (horizontal flow). A solution in the case of drains lying on the impervious layer is: $$\frac{L}{{H_m }}\left[ {4\frac{K}{R} + \left( {\frac{K}{R} - 1} \right)^2 s^2 } \right]^{1/2} $$ where K is the homogeneous and isotropic hydraulic conductivity, R the constant recharge-rate, s the slope, L the drain-spacing, H_m the maximal height of the water-table above the drains. This approximate solution yields results as accurate as other available solutions. Extensions are given for the case of drains located above the impervious layer and for vertically heterogeneous soils.     

User charges in irrigation: Potentials and limitations

Interest in systems of user charges for irrigation projects serving large numbers of small farmers has grown in recent years in response to concerns about

-the need to provide more adequate funding of O&M,

-distortions and inefficiencies induced by subsidies, and

-inadequate accountability of irrigation system managers to water users.

The effects that can be expected from a system of user charges depend on

-whether the charges are assessed as water prices or as area-based fees,

-whether the irrigation agency has a significant degree of financial autonomy, and

-the nature of the linkages between irrigation charges and investment decisions.

Other important considerations in establishing user charges are the ability of the users to pay irrigation fees; the cost-effectiveness of O&M activities; the costs of implementing the user charges; and whether charges are project-specific or uniform throughout a region or a nation.     

Layout structure of multi-quality irrigation networks: II��flexibility, separability and rigidity of networks

Three parameters were introduced here, in the second paper of the series, to evaluate layout structure of multi-quality water supply networks for irrigation. The first parameter was flexibility, which assesses the capability for a flexible supply of variable water quality values which can be obtained by dilution inside the network facilities. The second was separability which expresses the capability of the network to be divided into separate isolated sub-networks, each carrying a different water quality. The third was rigidity, which expresses a rigid allocation of one to one source?Cconsumer connections. Five types of network layout which were presented in Sinai (2011) were evaluated here, using these three parameters. The flexibility of a network was given special attention with the example of parallel and serial connection of fields to sources. A real example of a proposed network in the Hazeva region in Israel was analyzed. All feasible flow patterns (FFPs) were computed. The location of mixing and dilution junctions and computation of the QC feasibility domains were found and computed for every junction and consumer. Relative ranges of discharges and concentrations were conducted for all the FFPs found. However, no single optimal FFP with maximal flexibility was found. Therefore the FFPs were arranged in operational groups for possible sequential operation according to irrigation schedules.     

Effects of different irrigation regimes on a super-high-density olive grove cv. “Arbequina”: vegetative growth,productivity and polyphenol content of the oil

The effects of multiple irrigation regimes on the relationships among tree water status, vegetative growth and productivity within a super-high-density (SHD) “Arbequina” olive grove (1950 tree/ha) were studied for three seasons (2008–2010). Five different irrigation levels calculated as percentage of crop irrigation requirement using FAO procedures (Allen et al. in Crop evapotranspiration. Guidelines for computing crop water requirements. Irrigation and drainage paper 56. FAO, Rome, 1998) were imposed during the growing season. Periodically during the growing season, daytime stem water potential (Ψ _STEM), inflorescences per branch, fruits per inflorescence and shoot absolute growth rate were measured. Crop yield, fruit average fresh weight and oil polyphenol content were measured after harvest. The midday Ψ _STEM ranged from ?7 to ?1.5 MPa and correlated well enough with yield efficiency, crop density and fruit fresh weight to demonstrate its utility as a precise method for determining water status in SHD olive orchards. The relationships between midday Ψ _STEM and the horticultural parameters suggest maintaining Ψ _STEM values between ?3.5 and ?2.5 MPa is optimal for moderate annual yields of good quality oil. Values below ?3.5 MPa reduced current season productivity, while values over ?2.5 MPa were less effective in increasing productivity, reduced oil quality and produced excessive crop set that strongly affected vegetative growth and fruit production the following season. On the basis of the result given here, irrigation scheduling in the new SHD orchards should be planned on a 2-year basis and corrected annually based on crop load. Collectively, these results suggest that deficit irrigation management is a viable strategy for SHD olive orchards.     

Effect of long-term un-treated domestic wastewater re-use on soil quality, wheat grain and straw yields and attributes of fodder quality

In 2006 a comprehensive sampling program was undertaken in two pre-selected peri-urban villages in Faisalabad, Pakistan to evaluate the soil and agronomic impacts of long-term (25–30 years) untreated wastewater re-use on wheat grain and straw yields and attributes of wheat straw fodder quality. Soil SAR, ESP, RSC and ECe were 63%, 37%, 31%, and 50% higher under wastewater (WW) as compared with canal water (CW) irrigated plots. Further, 2.7 and 6.65 fold increases in soil NO ₃ ^? + NO ₂ ^? - N and Olsen-P were observed in WW as compared with CW irrigated plots. However, no significant differences in grain yield, wheat straw biomass, or fodder quality attributes were observed between WW and CW irrigated plots. In addition, for both CW and WW irrigated plots wheat straw, Cd and Pb concentrations were orders of magnitude below the EC Maximum permissible levels for Pb and Cd in feed materials and thus pose no threat to the fodder-livestock food chain. Further, elevated soil N associated with WW irrigated plots has a significant (p?<?0.01) positive influence on fodder quality by increasing the N content. Factorial ANOVA with covariance indicates that effective management of the elevated soil ECe in WW irrigated plots would increase grain yield and wheat straw biomass by 853 kg ha^?1 (19.5%) and 819 kg ha^?1 (18.6%) respectively as compared with CW irrigated plots. In Faisalabad, if managed appropriately to address emerging salinity issues the contribution of wastewater irrigation to the achievement of MDGs 1 and 7 could be significant if adverse impacts remain as marginal as found in this study.     

Development of the irrigation M&O learning process

A learning process has been developed, based on experiences in Thailand, Sri Lanka and Nepal, for improving the maintenance and operations practices of an irrigation project or system. This learning process has been designed to:

minimize the investment (O&M) costs so as to avoid rehabilitation;

increase credibility of irrigation project staff with central headquarters through improved financial management practices and accountability; and

develop more knowledge about what is occurring within the system in order to meet the needs of farmers.

     

Growth and yield of oleic sunflower (Helianthus annuus L.) under drip irrigation in very strongly saline soils

A four-year trial was set up to test the feasibility of growing oleic sunflower in a very strongly saline wasteland with drip irrigation in the Ningxia plain of Northwest China. The soil salinity expressed as electrical conductivity of the saturation paste extract (EC _e ) was around 28 dS/m, and soil nutrient was deficient in the upper 120 cm depth. The experiment included five soil matric potential (SMP) treatments, with the SMP at 20-cm depth immediately under the emitters maintained to be higher than ?5, ?10, ?15, ?20 and ?25 kPa after sunflower establishment. Drip irrigation consistently created a favourable soil moisture and low-salinity region in the root zone when the SMP was maintained higher than ?25 kPa. The sunflower dry seed yield decreased by 3.8 % for each unit increase in seasonal average soil salinity in the root zone. Plant vegetative growth, yield characteristics, irrigation frequency and irrigation amount all increased with the increase in SMP from ?25 to ?5 kPa, and the highest irrigation water use efficiency was available when the SMP was between ?10 and ?15 kPa (the amount of applied water was around 750 mm). Leaching of salts by drip irrigation gradually turned the very strongly saline soil into a moderately saline soil. This research suggests that drip irrigation can be successfully used in oleic sunflower cultivation in this highly saline soil and a SMP threshold between ?10 and ?15 kPa is suggested for irrigation scheduling.     

Fouling formation and chemical control in drip irrigation systems using treated wastewater

Drip irrigation systems are prone to changes in flow rate (FR) and increasing coefficients of variation (CV) when fed with treated wastewater, due to fouling inside the drippers. A model system was designed to measure the FR and fouling accumulation in laterals and drippers under different treatment conditions. A novel approach was taken to compare the different maintenance treatments. A comparison of chlorination and acidification strategies showed that daily chlorination and periodic acidification may prolong proper functioning of the drippers by maintaining a normal FR [(up to ±7 %) of nominal FR] and CV (<7 %) index in correlation with low fouling accumulation in the pipeline (<0.01 mg deposit/cm _pipe ² ). Current recommendations for the frequency of conventional treatments were found to be insufficient. Chemical analyses of the fouling inside the dripper and accumulated on the pipe wall showed that biofilm can survive inside the dripper under harsh environmental conditions, even when the pipeline stays clean. These results shed light on biofilm growth and survival mechanisms inside the dripper and may pave the way to developing new treatments or improving dripper design.     

Hydraulic model investigation of downstream erosion of large regulators: a case study

Flow conditions, which could not be explained, occurred in the stilling basin and outfall channel of the Feni Regulator sited at the western end of the Feni River closure dam. This regulator controls outflows from the upstream reservoir which supplies irrigation water to Muhuri Project in Bangladesh. Analysis of flood discharge data revealed that the design discharge for the structure was not exceeded; yet abnormal scour occurred in the outfall channel and the brick block rip-rap placed thereon was damaged. A model study was conducted to understand the causes of such unusual local erosion downstream of the stilling basin and to provide answers to two main questions:

-Is potential scour serious in terms of the stability of the structure?

-What protection measures could be taken to stabilize the scour at a safe level?

Using a 1:30 scale model, the probable maximum scour was simulated, and the performance of alternative rip-rap designs including that of the existing one were examined. The results of this study supplemented by field scour data collected during subsequent flood seasons indicated that even if the flow rate through the regulator approaches the design flood discharge, the downstream scour is not likely to extend up to an elevation of ? 10.7 m, a scour level observed in the previous year at a lower discharge. It also showed that the existing rip-rap blocks were marginally undersized and consequently the rip-rap was prone to failure if flow conditions departed from uniform. A suitable method of scour protection downstream of the stilling basin at the regulator exit also evolved from the study.     

The potential for farmer participation in irrigation system management

The management of most irrigation systems involves shared responsibility between one or more government agencies and farmers. Finding the optimal level of farmer management participation is an essential part of achieving optimal system performance. Two cases are discussed where farmers have been encouraged to play a more active management role with promising results. In the Gal Oya system in Sri Lanka, farmers manage the tertiary channels and also have a voice in managing the main system. In the Philippines, small systems have been turned over entirely to farmer management, while on large systems farmers manage the tertiary or secondary levels. A number of factors appear to be important in the management success of these irrigation systems including:

-the social environment,

-a manageable main system,

-a strong commitment by the irrigation agency,

-the use of community organizers, and

-construction tasks around which farmers can organize.

Greater farmer involvement in irrigation management can have both economic and social benefits. Economically there is evidence that farmers perform certain functions better than outside agencies can, and that both farmers and agencies perform their management tasks better when they feel a mutual responsibility for a common objective. Social benefits include the organizational skills that farmers learn and which may be useful in other activities, and a sense of self-respect and self-reliance. Though farmer participation requires a deliberate effort on the part of international and government agencies, as well as farmers, the benefits can be substantial.     

The Viejo Retamo secondary canal

The intended operation of the Rio Tunuyan irrigation scheme in the province of Mendoza, Argentina, is to divide flow proportionately over the entire area in accordance with registered water-rights. The main division of flow is by regulators at the heads of the lateral canals, which serve areas of appr. 15,000 ha. Taking the sub-lateral or secondary canal Viejo Retamo as an example, this paper discusses the flow division downstream of these regulators. The operation of the canal is evaluated with two performance indicators:

-the ratio of volume of water intended to be supplied to the tertiary units over the volume of water actually supplied, and

-the misallocation of water in volume.

In the Rio Tunuyan scheme, there is also a relation between the evapotranspiration of crops and the groundwater level: if less than 60% of the supplied canal water evapotranspires, the groundwater level rises.     

Computerised irrigation scheduling using spreadsheet models

Microcomputers are increasingly being used to help in the management of smallholder irrigation schemes in Third World countries. In many cases, commercially available spreadsheet packages offer advantages over established scientific programming languages. The paper starts with a review of computer models which have been developed for irrigation scheduling. Two criteria are identified which must be considered when developing computer models for this purpose: realistic data requirements and programs which are easy to understand. Spreadsheet packages provide a good introduction to computing and macro programming techniques can be used to customise spreadsheet models to create refined yet simple management tools. Two practical examples are presented from current research projects:

-a small scale scheme in Zimbabwe, where a spreadsheet model is used to produce irrigation schedules for smallholder farmers;

-a 20,000 ha project in Thailand, where a spreadsheet model makes use of feedback to improve main system scheduling.

     

Modeling a weak turbulent flow in a narrow and wavy channel: case of micro-irrigation

The baffle-fitted labyrinth channel is commonly used in micro-irrigation systems. The flow in this labyrinth channel has a rather low-Reynolds number. In addition, emitter clogging, which is the major drawback of the micro-irrigation technique, is significantly related to flow characteristics. In order to design an anti-clogging emitter with a good performance, the hydrodynamics must be understood and analyzed. As CFD modeling is nowadays the most efficient approach for improving emitter geometry, this paper presents assessment of several k–\(\varepsilon\) turbulence models for computation of micro-irrigation emitter hydrodynamics. The objective is to determine the simplest and most efficient model to improve emitter conception, in terms of both discharge/pressure loss and limitation of the areas where low velocity is likely to generate emitter clogging. Low-Reynolds number k–\(\varepsilon\) models are often assumed to be more suitable for the labyrinth-channel flow since these models have no wall functions, they can take into account low turbulence levels and they account for the effect of damped turbulence. The low-Reynolds number k–\(\varepsilon\) models used in the present study are compared to high-Reynolds number k–\(\varepsilon\) models. Very different trends are observed between low-Reynolds number k–\(\varepsilon\) models. Some models reproduce a turbulent behavior, while others reproduce a laminar behavior. The head loss analysis reveals that, contrary to classical smooth pipe flow, the contribution of turbulent dissipation cannot be neglected since its contribution is larger than wall friction ones. This feature explains why different models can induce quite different flow behavior.     

Sustainability of regulated deficit irrigation in a mid-maturing peach cultivar

The level of irrigation restriction to apply in a deficit irrigation (DI) programme for sustainable peach (‘Baby gold 6’) production was investigated. The experiment involved four irrigation treatments over five consecutive seasons (2007–2011). They were full irrigation (control), reducing irrigation by 20 % during the first half of stage III (DI-80 %), withholding irrigation until reaching a light stress level (DI-L) and withholding irrigation until reaching a moderate stress level (DI-M). The withholding of irrigation in both DI-L and DI-M was applied only during stage II and postharvest periods and was based on midday stem water potential thresholds (Ψ _stem). For the DI-L treatment ?1.5 MPa was used in both periods, and for DI-M ?1.8 and ?2.0 MPa were used during stage II and postharvest, respectively. Average Ψ _stem values during DI periods were approximately ?1.4 and ?1.2 MPa for DI-M and DI-L, respectively. The pre-defined thresholds required to trigger irrigation were rarely reached. No significant differences between treatments were found in terms of yield in any experimental year. However, DI-M and to a lesser extent DI-L had lower final fruit fresh mass at harvest related to lower Ψ _stem after three consecutive years of the experiment (during 2010 and 2011). Therefore, in terms of fruit size, DI was not sustainable. Rather than lowering Ψ _stem thresholds, we recommend discontinuing DI after 3-year application.     

Daylight crop water stress index for continuous monitoring of water status in apple trees

We studied the suitability of empirical crop water stress index (CWSI) averaged over daylight hours (CWSI_d) for continuous monitoring of water status in apple trees. The relationships between a midday CWSI (CWSI_m) and the CWSI_d and stem water potential (ψ _stem), and soil water deficit (SWD) were investigated. The treatments were: (1) non-stressed where the soil water was close to field capacity and (2) mildly stressed where SWD fluctuated between 0 and a maximum allowable depletion (MAD of 50 %). The linear relationship between canopy and air temperature difference (ΔT) and air vapor pressure deficit (VPD) averaged over daylight hours resulted in a non-water-stressed baseline (NWSBL) with higher correlation (?T = ?0.97 VPD – 0.46, R ² = 0.78, p < 0.001) compared with the conventional midday approach (?T = ?0.59 VPD – 0.67, R ² = 0.51, p < 0.001). Wind speed and solar radiation showed no significant effect on the daylight NWSBL. There was no statistically meaningful relationship between midday ψ _stem and CWSI_m. The CWSI_d agreed well with SWD (R ² = 0.70, p < 0.001), while the correlation between SWD and CWSI_m was substantially weaker (R ² = 0.38, p = 0.033). The CWSI_d exhibited high sensitivity to mild variations in the soil water content, suggesting it as a promising indicator of water availability in the root zone. The CWSI_d is stable under transitional weather conditions as it reflects the daily activity of an apple crop.     

Performance evaluation and calibration of soil water content and potential sensors for agricultural soils in eastern Colorado

This study evaluated the performance of three soil water content sensors (CS616/625, Campbell Scientific, Inc., Logan, UT; TDT, Acclima, Inc., Meridian, ID; 5TE, Decagon Devices, Inc., Pullman, WA) and a soil water potential sensor (Watermark 200SS, Irrometer Company, Inc., Riverside, CA) in laboratory and field conditions. Soil water content/potential values measured by the sensors were compared with corresponding volumetric water content (θ_v, m³ m⁻³) values derived from gravimetric samples, ranging approximately from the permanent wilting point (PWP) to field capacity (FC) volumetric water contents. Under laboratory and field conditions, the factory-based calibrations of θ_v did not consistently achieve the required accuracy for any sensor in the sandy clay loam, loamy sand, and clay loam soils of eastern Colorado. Salt (calcium chloride dihydrate) added to the soils in the laboratory caused the CS616, TDT, and 5TE sensors to experience errors in their volumetric water content readings with increased bulk soil electrical conductivity (EC; dS m⁻¹). Results from field tests in sandy clay loam and loamy sand soils indicated that a linear calibration (equations provided) for the TDT, CS616 and 5TE sensors (and a logarithmic calibration for the Watermark sensors) could reduce the errors of the factory calibration of θ_v to less than 0.02 ± 0.035 m³ m⁻³. Furthermore, the performance evaluation tests confirmed that each individual sensor needed a unique calibration equation for every soil type and location in the field. In addition, the calibrated van Genuchten (1980) equation was as accurate as the calibrated logarithmic equation and can be used to convert soil water potential (kPa) to volumetric soil water content (m³ m⁻³). Finally, analysis of the θ_v field data indicated that the CS616, 5TE and Watermark sensor readings were influenced by diurnal fluctuations in soil temperature, while the TDT was not influenced. Therefore, it is recommended that the soil temperature be considered in the calibration process of the CS616, 5TE, and Watermark sensors. Further research will be aimed towards determining the need of sensor calibration for every agricultural season.