The reorganization of water users' associations in Mendoza,Argentina

This paper describes the changes introduced in water users' associations in the Province of Mendoza, Argentina. Before 1985 there were 709 water users' associations, known as Canal Inspection, each of them in charge of the administration of an area of about 300 ha, corresponding to tertiary and quaternary canals. At present there are 21 reorganized inspections administering an average area of 6 000 ha. The democratic system for the election of authorities is described and the method of budget preparation and control is discussed. The advantage of reorganization is illustrated through the economic assessment of the Reduccion Main Canal. This canal irrigates an area of 13 985 ha. The annual benefits due to reorganization are estimated to total A 32 800 (US$ 41 000), being 2.1 times the annual budget of the Inspection.     

Photosynthesis,leaf conductance,and water relations of cowpea under saline conditions

Summary Cowpea (Vigna unguiculata L.), grown widely under both irrigated and dryland conditions, is well adapted to drought and high temperature and is moderately salt tolerant. Data on photosynthetic response and regulation of water relations in cowpea under salinity stress is lacking. Therefore, in conjunction with a field plot experiment to establish the leaching requirement of cowpea, measurements were made of carbon dioxide assimilation rates (A) by ¹⁴CO₂ uptake, leaf conductances to H₂O (g₁) by tritum uptake, and to CO₂ (g), and leaf total water potential (_t ¹) and osmotic potential ( ¹).Cowpeas, grown in field plots containing Pachappa fine sandy loam (mixed, thermic, Mollic Haploxeraff), were irrigated daily with saline water (1,350 mg 1^–1 total salt concentration) to achieve leaching fractions of 0.17, 0.13, 0.09, 0.07, and 0.02. Cowpea maintained high leaf water potentials, high rates of CO₂ assimilation and high leaf conductances under moderately saline conditions (high leaching). Values of _t ¹ and ¹ for high leaching were consistently 50 to 200 J kg^–1 higher than for low leaching throughout the day. Calculating ¹ at full leaf turgor eliminated diurnal variation in ¹. As leaching decreased, however, A, g₁, and g, decreased significantly. About 45% of the 1°C assimilated by the leaf was incorporated rapidly into ethanol insoluble compounds. The relationship between A and g₁ for cowpea was similar to that reported for other crops.Contribution from the US Salinity Laboratory, USDA-ARS, 4500 Glenwood Dr., Riverside, CA. 92501, USA     

Plant indicators of wheat and soybean crop water stress

Summary The onset of water stress within a crop is defined as the time at which the rate of water loss declines below that of a well watered crop in the same locality. The relation to the onset of water stress and soil water status of several readily measured plant parameters was investigated in crops of wheat and soybeans over three years. Evapotranspiration ET was monitored with weighing lysimeters. A noticeable decline in the rate of ET for both wheat and soybeans was detected once 20% to 30% of the total plant available water PAW remained in the 1 m deep lysimeter soil profile. Extension growth of wheat declined when PAW was 33% and 34% in two years of measurement. In soybeans, the decline in the rate of leaf extension coincided with the decline in the rate of ET. Midmorning measurement of exposed leaf water potential _L, covered leaf water potential _CL and covered plant leaf water potential _CP yielded similar results for both wheat and soybeans. Day-to-day variability was least in _CP and most in _L. Values of _CP, _L and _CL decreased rapidly with PAW < 30%. Daily values of leaf diffusive conductance were variable but there was a general decline in conductance with PAW < 30%. It is suggested that _CL may be the easiest and most reliable parameter to monitor as a means of detecting the onset of stress. The results indicated that PAW levels in the root zone of 50% for wheat and 30% for soybean probably do not affect extension growth or plant water status parameters and can thus be used as criteria for irrigation scheduling.Seconded from the Water Research Commission, Pretoria; present address: CSIRO, Division of Irrigation Research, Griffith, N SW 2680, Australia     

Irrigation scheduling in a mature peach orchard using tensiometers and dendrometers

Three trickle irrigation schedules, two of which were scheduled according to soil water potential ( soil) (tensiometer method) and daily stem contraction (DSC) (dendrometer method) respectively and the other one was a schedule of restricted water supply, were applied to a mature peach orchard.The annual water application based on soil was greater than that based on DSC. However, tree growth, fruit size and leaf water potential (leaf) on the trees in the dendrometer scheduling plot did not differ from those in the tensiometer scheduling plot while the premature fruit drop and fruit bud initiation were greatly different. The restricted water supply treatment limited significantly both tree and fruit growth. In addition, the lower leaf was observed on the trees in this plot.Further study shows that use of the dendrometer method for scheduling irrigation satisfies the water needs of the plant and that the tensiometer method is less accurate.Abbreviations leaf leaf water potential - soil soil water potential - DSC daily stem contraction - LVDT linear variable displacement transducer - PET potential evapotranspiration     

Infiltration and runoff as affected by pitting,mulching and sprinkler irrigation

Summary Changes in infiltration and runoff caused by pitting and mulching under sprinkler irrigation were studied on two soil types. Pitting or diking was done with an implement called a dammer-diker. Five soil treatments were applied: shallow and deep dammer-diker, shallow dammer-diker with mulch, bare, and a mulched soil, combined with two water application rates. Total water infiltration and runoff varied during the experiment. Runoff decreased with area of water storage provided by the pits and the less water was applied. Mulch treatments also reduced runoff. Surface water storage decreased during the season. Changes in soil physical properties due to pitting were more important in controlling runoff than surface water storage.The effective saturated hydraulic conductivity of the soil progressively decreased through the season for all soil treatments and water application rates.A model was developed to simulate the effect of pits on runoff. On a silt loam soil, simulated percent runoff and accumulated runoff over time for the bare and pitted treatments agreed closely to measured values. The agreement of simulated to measured runoff for a silty clay loam soil was not as good probably because of cracking which the simulation model did not take into account.     

Procedure for predicting and designing moving sprinkler application patterns

Summary Water application pattern, WAP, is one of the most important factors that determine the instantaneous and the cumulative application rates of moving irrigation machines. The mathematical background of a procedure to predict and design the WAP of moving irrigation machines is introduced. It includes a mathematical analysis of the effect of pressure head, height and spacing between emitters on the WAP, and a nomograph that presents this analysis graphically and illustrates the design procedure of the application pattern of irrigation machines.Abbreviations P()a water application rate at a normalized radial distance from the emitter [m/s] - ka number of linear segments needed to represent the pattern - s/Ra normalized radial distance from the emitter - Ra wetted radius [m] - sa radial distance from the emitter [m] - n _j n _i/ha normalized water application rate at point - j, ha maximum water application rate [m/s] n _j water application rate at point j [m/s] - _j =m _j/Ra normalized radial distance of point j from emitter - m _ja radial distance of point - ja from emitter [m], CWAP - (x)a Cumulative Water Application Pattern: amount of water per unit area applied at a distance - xa from the travel path of the emitter [m³/m²] - xa distance from the travel path of the emitter [m] - T _xa time of application at a distance - xa from the travel path of the emitter [s] - va velocity of propagation of the machine [m/s] - k ₁a the outmost linear segment that its radial distance from the emitter - m _k1a is smaller than the distance of the travel path from the emitter - x, T _ja time at which the - j ^tha linear segment (ring) stops influencing the point located at a distance - xa from the emitter - ₁, ₂, ₃a dimensionless numbers derived by dimensional analysis - ua water jet velocity [m/s] - ga gravity acceleration [m/s²] - da nozzle diameter [m], v kinematic viscosity [m²/s] - Ha emitters height [m] - , a regression analysis coefficients - Paa Pattern fit coefficient for water application - F(r)a normalized desired water application pattern [1/m] - f(r)a normalized actual water application pattern [1/m] - La common distance on which - F(r) and f(r)a are defined [m], SP spacing interval between emitters [m] - DSa dimensionless spacing interval between emitters - DSa variation of dimensionless spacing interval - Paa variation of Pa coefficient - Pa pressure head [kPa]     

Leaching of soluble salt during infiltration and redistribution

Summary The paper reports an experimental study of miscible displacement of soluble salts during infiltration and redistribution of water in vertical, homogeneous columns of sandy, sandy loam and clay soils with initially uniform salt and moisture contents. Calcium chloride, mixed uniformly in initially dry and moist soils, was leached with water under transient and steady infiltration conditions. The salt and water profiles were determined immediately following infiltration and after matching total infiltration and redistribution times. Irrespective of different flow conditions and soil types, the centre of mass of salt front coincided with the piston front that would exist given perfect displacement of water initially present in the soil by the water being infiltrated (piston-flow model). Furthermore the advance of centre of mass of salt front was independent of the water application rate and initial soil water content in all soils following both infiltration and redistribution.     

Integrating and applying soil and plant water status measurements

Summary Application of soil and plant water status measurements requires some model of the soil-plant-atmosphere system because the measurements made refer to only part of the complex whole. Measurements need to be made to check on the validity of the model and to facilitate adjustment. Since models are only a small imitation of reality they need to be continually checked if application of the results are to be useful. The temptation to use models without checking should be discouraged — modelers should keep one foot in the field.     

Effects of salinity on germination,seedling growth,and yield of melons

Summary Four melon (Cucumis melo L.) cultivars were tested for salt tolerance at germination, seedling growth stages, and plant maturation. Noy Amid was the most tolerant during germination, achieving 56% germination in 15,000 mg/l NaCl solution. However, this cultivar and Eshkolit Ha 'Amaqim were relatively sensitive during the first 4 days' growth of the radicle and the hypocotyl, and the first 3 weeks' development of the seedling. Their yields were reduced under saline as compared with non-saline field conditions. In contrast, Honey Dew and Rochet had little or no germination in 15,000 mg/l NaCl but showed salt tolerance during seedling growth stages. Yield of Honey Dew was unaffected by saline field conditions, and that of Rochet was not significantly reduced from the non-saline control. Thus, selection for salt tolerance in melons appears feasible during early vegetative growth stages but not during germination.Contribution No. 1032-E, 1984 series, from the Agricultural Research Organization, Bet Dagan, Israel     

Effect of soil water osmotic potential on growth and water relationships in barley during soil water depletion

Summary Barley plants (Hordeum distichum, L., cv. Zita) grown in a sandy soil in pots were adjusted during a pretreatment period of 5 days to three levels of soil water osmotic potential by percolating 61 of a nutrient solution with additional 0, 22.3 and 44.6 mM KCl. A drying cycle was then started and the plants were harvested when the soil water matric potential had decreased to –1.4 MPa, respectively 6, 7 and 8 days later.No significant differences in dry matter yields, transpiration coefficients and wilting percentages were found between treatments.During the drying cycle leaf water potential ( _l ) decreased concomitantly with decrease in soil water potential ( _s ) with almost constant and similar differences ( _l – _s ) for all treatments despite differences in levels of potentials. The concomitant decrease in leaf osmotic potential () was due partly to dehydration (58%) and partly to increase in leaf solute content (42%) independent of treatment. The part of total osmotic solutes due to K decreased relatively during the drying cycle.Close relationships were found between and _l as functions of relative water content (RWC). Identical curves for the two levels of salt treatment agree with similar concentrations of K, Cl, and ash found for salt treated plants indicating that maximum uptake of macro nutrients may have been reached.During the main part of the drying cycle the turgor potential as function of RWC was higher and decreased less steeply with decreasing RWC in the salt treated than in the non-salt treated plants.In the beginning of the drying cycle additions of KCI lowered the transpiration rates of the salt treated plants resulting in a slower desiccation of the soil and hence an increased growth period. A delay in uptake from a limited soil water supply may be advantageous during intermittent periods of drought.     

Modernization of irrigation systems: A case of research,oriented to improve management

In recent years, the traditional concept of an irrigation project has been changing. From just a physical structure for the storage, conveyance and distribution of water, it is now being regarded as a more complex system, including farmers' participation. This implies an improved management in all phases, from reservoir operation to farm management, and therefore the change from simple operation and maintenance to operation, maintenance and management.To face this new challenge, existing projects must be modernized. The Sorraia Irrigation Project is one of those projects. In this paper major problems are identified and it is showed how research (namely through modelling) can be oriented towards an improved management, regarding the conveyance and distribution systems as well as the on-farm systems.Finally it becomes evident that beyond the technical problems to be solved, the involvement and participation of farmers must be improved at all levels of management. Hence, there is also a need for implementing programs on education, training and extension.     

Potassium induced improvement of yield response in barley exposed to soil water stress

Summary The interaction of different K status of barley plants (Hordeum vulgare, L.) and water stress on yield and water relations was studied. The plants which were cultivated outdoor in pots and supplied with 0.8, 5.0, 8.5 or 12.0 g K per pot, as KCl, were subjected to increased soil water stress during the early grain filling stage.The water content of the flag leaf tissue was significantly increased from 3.1 to 4.1 g H₂O/g D.M. (dry matter) by K application resulting in maintenance of similar leaf osmotic potentials (–1.5 MPa) at all K levels prior to onset of water stress (Table 2). At the lowest K level Ca contributed essentially to maintenance of the cell osmotic potential (Fig. 2).In fully watered plants grain yield at the lowest K level was reduced 20% (Fig. 5 a) due to a decrease in the number of tillers with ears per plant (Fig. 5 b) and to early commencement of maturity processes (Table 3).Water stress caused grain yield reductions between 15 and 50%. However, by increase of K application yield was maintained to the greatest degree in high K plants (Fig. 5 a) due to improved water status in these plants during the drying cycle (Fig. 4). The production of above ground dry matter (top D.M.) during the grain filling period and the grain yield were highly correlated with the leaf water content at the end of the drying cycles (Fig. 6). The greater yield in high K plants was associated with prolongation of the grain filling period by up to 7 days (Table 3) and with an increase in grain weight by up to 20% (Fig. 5 b) as compared with low K plants. Preanthesis reserves contributed up to 52% of grain yield at low K levels (Fig. 5 c) reducing differences in grain yield between the K levels.Abbreviations RWC predawn relative water content - predawn leaf osmotic potential - WUE water use efficiency - R preanthesis reserves - ear D.M. increase in ear D.M. during the grain filling period - top D.M. increase in top D.M. during the grain filling period - SD standard deviation - LSD least significant difference     

Rapid field evaluation of drip and microspray distribution uniformity

The Cal Poly ITRC irrigation evaluation programs have been widely used to assess the global distribution uniformity (DU) of drip and microsprayer irrigation systems. The field procedures and formulas used in the program are presented in this paper. The system DU is estimated by mathematically combining the component DU values. DU components include pressure differences, other causes (such as manufacturing variation, plugging, and wear), unequal drainage, and unequal application rates. Results are presented from evaluations by several entities, including Cal Poly ITRC. Cal Poly evaluations of 329 fields provided an average DU_lq of 0.85 for drip and 0.80 for microspray. Approximately 45% of the non-uniformity was due to pressure differences, 52% was due to other causes, 1% due to unequal drainage, and 2% due to unequal application rates. The data show that with good design and management, it is possible to have high system DU values for at least a 20-year system life.     

Yield and vegetative growth as related to plant water potential of cotton irrigated with a moving sprinkler system at different frequencies and wetting depths

Summary Seed-cotton yield, yield components and vegetative growth were determined under different irrigation frequencies and wetting depths with a self-propelled moving-irrigation-system (MSIS) in 1986 and 1987. Irrigation timing was determined in both years by pre-irrigation, mid-day plant water potential (_w). The amount of water to be applied was determined by measuring the soil moisture deficit. In 1987, the effect of a change from one irrigation frequency and wetting depth to another at mid-flowering was also examined. Linear responses of relative seed-cotton yield to the amount of evapotranspiration (ET) were found for both years with similar slopes but different intercepts. Significant positive regressions were obtained between pre-irrigation plant _w and relative seed-cotton yield, and vegetative growth during the linear growth stage. Seed-cotton yield was affected by both wetting depth and pre-irrigation plant _w. The deeper the irrigation the higher was the seed-cotton yield for each pre-irrigation plant _w. Irrigation frequencies which maintained plant _w above -1.5 MPa during vegetative growth, flowering and boll-filling resulted in maximum production. The boll filling stage appeared to be a very sensitive one, as boll weight was found to be the main yield component responding to irrigation treatments. At a wetting depth of 120 cm, higher seed-cotton yields were obtained than at a more shallow wetting. Different irrigation managements resulted in different turgor potentials (_t) mainly during mid-day. Both leaf water vapour conductance and net assimilation rate were sensitive to leaf _w.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagon, Israel, No. 2903-E, 1990 series. Research was supported by the U.S.-Israel Binational Agric. Res. and Develop. Fund.     

Mungbean response to irrigation with waters of different salinities

Summary Experiments were conducted in lysimeters (1985) and field plots (1986) to evaluate changes in soil moisture and salinity status following irrigations with different blends of a saline water, SW (EC_iw = 6.4 dS/m) and non-saline water, NSW (0.3 dS/m) and their effects on the growth and yield of Mungbean (Vigna radiata L. Wilczek). Normalised to the yield of the treatment receiving NSW (100%), relative seed yields (RY) declined to 73, 11 and 3%, respectively, for the treatments receiving SWNSW blends of 12 (2.5 dS/m), 21 (4.7 dS/m) and SW as such. RY increased to 64 and 74% when NSW was substituted for presowing irrigation and 21 SWNSW blend and SW, respectively were used for postsowing irrigations. Due to moderating effect of rainfall (9.8 cm) during the growing season of 1986, valus of RY obtained with 12 and 21 SWNSW blends were 81 and 42% and increased to 96 and 82% when these waters were applied after presowing irrigation with NSW. Irrigation at presowing with non-saline water leached the salts of shallow depths leading to better germination and initial growth. In addition, plants were able to extract greater amounts of water even from deeper soil layers. The RY of Mungbean was related to the weighted time averaged salinity of the 0–120 cm soil depth (EC_e) by RY = 100-20.7 (EC_e-1.8). The study indicated that applying NSW for presowing irrigation to Mungbean is more beneficial than using it after blending with saline water.     

Relationships between crop temperature,grain yield,evapotranspiration and phenological development in two hybrids of moisture stressed sorghum

Summary Recent studies have shown that the grain yields of corn (Zea mays L.) and wheat (Triticum aestivum L.) are related to the degree of water stress they undergo. The purpose of the study reported here was to establish relationships between crop temperature and the grain yields, phenological development, evapotranspiration rates (ET) and leaf water potential ( _l ) of two hybrids of grain sorghum (Sorghum bicolor L. Moench) subjected to varying levels of plant water stress. The study was conducted at the University of Nebraska Sandhills Agricultural Laboratory in 1978 on a Typic Ustipsamment (Valentine fine sand) soil. The sorghum hybrids used were RS 626 and NB 505. Four irrigation treatments were applied in order to subject the crops to varying levels of water stress during each of three major growth stages. Soil moisture was monitored with a neutron probe. ET was estimated with the water balance technique. Crop temperature was measured with an IR thermometer and leaf water potential was measured with a Scholander pressure bomb. Grain yields were reduced by water stress occuring at anytime during the growing season. Yield reductions were largest when stress occurred during only the grainfill period and were least when stress occurred during the entire growing season. The percentage reduction in sorghum grain yield can be described by an index involving the seasonal accumulation of the daily mid-day temperature differences between well-watered and stressed crops ( TSD). As TSD values increased, ET decreased. However, the correlation of ET with TSD was relatively low (R² = 0.60) probably due to the limited amount of data available for analysis and inaccuracies in the soil water balance method used to estimate ET. The mid-day temperature of well-watered rows ranged between 18.0 and 32.8 °C with a mid-day temperature range of about 0.5 °C between the well-watered rows in various plots for several days following an irrigation. However, in certain instances, the mid-day temperature range increased to 1–2 °C for a few days before irrigation. This suggests that certain of the rows experienced water stress and should have been irrigated earlier. Yield data support that conclusion. Range in crop temperature within a field appeared to be a sensitive indicator of crop water stress in sorghum. No significant difference in the phenological development of sorghum resulted from water stress except in one NB 505 plot in which plants were stressed throughout the entire season. In that plot, the stressed plants lagged in development behind non-stressed plants by approximately ten days. The differences in mid-day leaf water potentials ( _l ) and crop temperatures (T) between stressed and non-stressed vegetation were examined. As T increased up to about 4 °C, _l , also increased. Beyond that point, _l decreased while T continued to increase. This behavior was attributed to stomatal closure which permitted an increase in _l of the stressed plants (hence reducing _l ) even as T continued to increase.Published as Paper No. 6551, Journal Series, Nebraska Agricultural Experiment Station. The work reported was conducted under Regional Research Project 11–33 and Nebraska Agricultural Experiment Station Project 11–50. The work upon which this publication is based was supported in part by funds provided by the Office of Water Research and Technology B-044-NEB, US Department of the Interior, Washington, DC, as authorized by the Water Research and Development Act of 1978. This article was sponsored in part by the Nebraska Water Resources Center, Institute of Agriculture and Natural Resources, University of Nebraska-LincolnResearch Assistant, Associate Professor, Research Assistant, and Associate Professor, University of Nebraska, Lincoln. Contents of this puplication do not necessarily reflect the views and policies of the Office of Water Research and Technology, US Dept. of the Interior, nor does mention of trade names or commercial products constitute their endorsement or recommendation for use by the United States Government     

Water-conserving wheat irrigation schedules based on climatic records

Summary Correlations between spring rainfall and grain yield were determined for four winter wheat cultivars (Triticum aestivum L. em. Thell. Triumph, Wichita, Concho, and Triumph 64), grown between 1950 and 1977 under dryland conditions at Stillwater, in the East Central region of Oklahoma, and at Goodwell, located in the drier, western part of the state.At Stillwater, all but one of the cultivars exhibited maximum positive correlations between rainfall and yield in the fourth week of March, when stem-extension occurs. Smaller positive correlations were observed in mid-April when flowering. Results at Goodwell were similar except that the correlations between rainfall and yield were lower and occurred earlier than at Stillwater and showed a less marked secondary peak at flowering. These results agree with those of experiments in which irrigation has been applied at different growth stages of wheat, and have shown that both stem-extension and flowering are critical stages of water requirement. As the results of this climatic study show that the peak correlations between rainfall and yield occur at these same two stages, it is suggested that long-term climatic data could be used to determine optimum timing for irrigation of wheat.Such an approach should save water and energy by limiting irrigation to those times when analysis of local records demonstrates the maximum positive correlation between rainfall and yield.     

Pressurised irrigation technologies for smallholders in developing countries – a review

The findings of a study of factors influencing the uptake of pressurised irrigation technologies by smallholders in developing countries are presented. The paper reviews the physical and technical characteristics that determine their suitability for use by smallholders. It also identifies a range of pre-conditions relating to water availability, institutional support and economic opportunity that must be satisfied before smallholders will adopt even low-technology pressurised irrigation systems.The review demonstrates that where physical, economic and institutional conditions are right some forms of pressurised modern irrigation technology permit smallholder irrigation of high value crops where surface irrigation would be inappropriate. However, the paper warns against the danger of wide-scale promotion of such technologies without considering the issues of institutional and technical support. Where pressurised systems are promoted to increase water use efficiency it is essential that they be well designed, installed and operated for savings to be realised.     

Pressure chamber procedures for leaf water potential measurements of cotton

Summary Measurement of leaf water potential ( _l ) with a pressure chamber is usually regarded as a reliable and practical field technique. However, recent evidence indicates that results depend on the measurement techniques employed. Field experiments were conducted to identify the magnitude and sources of error affecting pressure chamber measurements of _l in cotton (Gossypium hirsutum L.) and to develop an accurate and operationally flexible procedure. Water potential of bare cotton leaves was about 0.2 MPa less than aluminum foil wrapped leaves when the elapsed time between excision to chamber pressurization was less than 30 s. The water potential of intact leaves increased 0.3 MPa after 15 s of enclosure in aluminum foil. 5 to 30 min of enclosure were sufficient to reach equilibrium between _l and water potential within the plant stem. Aluminum foil wrapped leaves maintained their _l for 2 h stored in a humid, dark box at 21–28 °C while wet wrapped (cheesecloth) or bare leaf _l increased after one hour because of hydration. An accurate and operationally flexible _l measurement procedure, suitable for large scale sampling, was defined.Contribution from the USDA-ARS, Water Management Research Laboratory, 2021 S. Peach, Fresno, CA 93727 and the Dept. of Land, Air and Water Resources, University of California, Davis, CA 95616, USA     

The legal and administrative setting for the use of water resources in Mendoza, Argentina

The legal-administrative setting for the use of waterresources in Mendoza Province is founded on differentlegal rules. This includes the National Constitution,the Argentine Civil Code, National Laws, theConstitution of the Provincial State, the GeneralWater Law, (legal) administrative regulations of theGeneral Department of Irrigation.The current water law is based on the roman law, onthe Arab irrigation water rights which were brought toArgentina by the Spaniards and on the practices of theoriginal American pre-Colombian intermediate law.The latter is marked by a strong regional sense. Assuch, the water law is strongly influenced by theregions elements of nature and attempts to offersolutions to problems.The legal rules are discussed from a behavioral andorganizational perspective. Examples from the LowerTunuyan System are given to illustrate the day-to-dayeffects on irrigation water management.