Processes of salinization and strategies to cope with this in irrigation in Santiago del Estero

Transcription

1 Processes of salinization and strategies to cope with this in irrigation in Santiago del Estero MSc thesis TUDelft by Maria Alcaraz Boscà Supervisors: Dr.ir. Maurits Ertsen Prof.dr.ir. Nick van der Giesen

2 Abstract In arid and sei-arid regions, salinity is one of the ost iportant probles that affect the irrigation systes. This is the case of Rio Dulce irrigation syste. The Proyecto Rio Dulce is an irrigation syste located in the province of Santiago del Estero in Argentina. This syste is characterized by having irrigated and non-irrigated fields where salinization occurs due to capillary rise. In this thesis, the evolution of salinity on the fields has been studied at sall and large scale with different odels: the WASIM odel (sall scale) and the SALTMOD odel (large scale). Also, several possibilities of soil reclaation in the area have been considered in order to know how the syste behaves given different options of drainage and irrigation. Finally, it can be concluded that reclaation of the soil is feasible with the installation of a drainage syste and the application of irrigation in the (until now) non-irrigated fields. Page of 49

3 Table of contents ABSTRACT...1 TABLE OF CONTENTS INTRODUCTION Irrigation systes & salinity probles Rio Dulce Irrigation Project Brief description of the irrigation syste Data related to salinity in the current PRD Structure of this thesis... 9 THE MODELS The WASIM odel The SALTMOD odel STUDY OF SALINITY WITH WASIM Evolution of salinity at sall scale Reclaation experient executed in the Pilot Area of Drainage and Soil Reclaation at INTA-EEASE Using the WASIM odel to study and odel reclaation experient at Lote Study of required inputs Calibration Salinity Conclusions Possibilities of soil reclaation in PRD Conclusions STUDY OF SALINITY WITH SALTMOD Study of salinity in the PRD at larger scale Calibration Different scenarios Inputs variables Conclusions Possibilities of soil reclaation in PRD... 4 Page 3 of 49

4 4..1 Drainage Drainage & Irrigation Conclusions CONCLUSIONS BIBLIOGRAPHY...48 Page 4 of 49

5 1 Introduction 1.1 Irrigation systes & salinity probles In those irrigation systes that are located in arid or sei-arid areas, the salinization of the soil is a coon proble. When the soils of these regions are irrigated, the natural conditions of the area change copletely and percolation increases considerably. Generally, this aount of water percolating in the soil is higher than the drainage capacity of the soil and the groundwater table level becoes shallow. If this water is used by the plants to transpire by eans of capillary rise, then the salinity of the soil will increase since the water that is transpirated leaves behind the salts it contained. If irrigated and non-irrigated fields can be distinguished in the irrigation schee, the salinization will take place in the non-irrigated fields. This is because in these fields there is not percolation fro the surface that counteracts the effect of capillary rise. This is the case of the irrigation syste that will be studied in this work, The Proyecto Dulce Irrigation Syste where those fields that are nonirrigated have serious probles with salinity. As an exaple, in the graphs shown below it can be seen the salinity levels in different fields: two irrigated and two non-irrigated. In the non-irrigated fields, salinity reaches very high levels whereas in the irrigated fields the salinity values are suitable for agricultural use. In the irrigated field the salinity values increase during the dry season (May-October) because of capillary rise. Later, when the growing season starts salinity levels decrease thanks to rainfall and irrigation that reove salts fro the topsoil. On the contrary, in the non-irrigated fields the salinity levels increase in the wet season (Noveber-April) because of the growing of natural vegetation like plants. Graph 1 Salinity levels in irrigated and non-irrigated fields in PRD Prieto D. & Angueira C La dináica de la salinidad en los suelos bajo riego y su relación con el anejo del agua. Page 5 of 49

6 1. Rio Dulce Irrigation Project 1..1 Brief description of the irrigation syste The Rio Dulce Irrigation Project (PRD) is one of the ost iportant irrigation systes in Argentina. It is located in the province of Santiago del Estero which is one of the poorest of the country. Santiago del Estero is placed in the north of Argentina between the south latitudes 3º9 and 5º38 and west longitudes 61º4 and 65º11. This is a seiarid area with a ean annual teperature of 1.5 ºC. Winters are dry and suers are wet and hot. The annual precipitation ranges fro 5 to 8 /year while the potential evapotranspiration ranges fro 13 to 16 /year, so the annual water balance is negative in all the areas. The Rio Dulce irrigation project is located in the iddle part of the Rio Dulce basin which covers the provinces of Tucuán, Santiago del Estero and Córdoba. It is divided in five different zones according to historical reasons and the different odernization of each one. The axiu irrigable area of the PRD is about 1, ha but its gross coand area is about 35, ha. However, the irrigated area has never reached 1, ha, so water has never been scarce. In the syste it can be distinguished irrigated and non-irrigated fields. Also, the shape of the parcels varies Figure 1: Political ap of Argentina fro a few hectares to ore than 1 hectares per field. In the next table the distribution and size of the parcels is shown: HOLDINGS Size of parcels Nuber % Total/Mean Table 1: Holding size distribution in PRD Page 6 of 49

7 Figure Holding size distribution in PRD 1.. Data related to salinity in the current PRD In Daniel Prieto s thesis: Modernization and the evolution of irrigation practices in the Rio Dulce irrigation project there is data about salinity levels, irrigation and rainfall in soe areas (cases) of the irrigation syste. In the next tables, this data is shown. SALINITY LEVELS (ds/) N IRRIGATED FIELD NON-IRRIGATED FIELD CASE CASE CASE N= nuber of sapled cases Table Average soil salinity of irrigated and not irrigated parcels in three sapled areas. Salt concentrations of the soil are expressed in ECe, the electric conductivity of an extract of saturated soil paste. Also, for Case 1 data of salinity of irrigation water and groundwater are available. It can be noticed that ground water salinity is 1 ties higher than irrigation water salinity. This fact has favored secondary salinization in the area. Page 7 of 49

8 In this area, the water table reains at around eters depth at present, where it stabilizes due to evapotranspiration. EC (ds/ 5 C) IRRIGATION WATER WATER TABLE Table 3 Salinity of irrigation and groundwater in Case 1 In the next nubers, data of irrigation and rainfall in several areas of the irrigation syste are shown. January February March April May June July August Septeber October Noveber Deceber Total irrigation () Official Schedule Case Case Case Case = irrigation turn; = no irrigation turn Table 4 Official irrigation schedule and real irrigation schedules at different areas of PRD EFFECTIVE PRECIPITATION Mean January February March April May June July August Septeber October Noveber Deceber Total precipitation Table 5 Effective precipitation for different growing seasons, Page 8 of 49

9 Finally, the potential evapotranspiration obtained for each onth. Potential ET (/day) January February March April May June July August Septeber October Noveber Deceber Table 6 Potential evapotranspiration 1.3 Structure of this thesis As it is said before, the Rio Dulce irrigation syste has serious probles with salinity. In order to find a solution to this proble, this thesis has been focused in these ain parts: Firstly, to study the salinity process in the fields: which is the behavior of the salts in the fields within the years (sall scale) and also, over the years (large scale). Lately, consider the different possibilities of soil reclaation in the area. The objective of this point is not to find the perfect solution to the salinity proble but to observe how the syste behaves in front of different actions. Therefore, siulation odels are helpful to develop and evaluate drainage and irrigation strategies once calibrated using experiental data. In this case two different odels have been used: The WASIM odel used to study salinity at sall scale. The SALTMOD odel utilized to study salinity at large scale. Between these odels there are several differences as it is explained later. The ost iportant one is the tie-step used to carry out the water and salt balances: SALTMOD does a seasonal water balance while WASIM has a daily tie-step. The reasons why two odels are used are: fro one hand, to copare both odels and check how different the results are and by the other hand, to evaluate the applicability of these odels for the Rio Dulce Irrigation Syste. Page 9 of 49

10 The odels In this section, the two odels that have been used in this thesis are explained with ore detail..1 The WASIM odel A general description of the WASIM odel as given in Meenakshi Hirekhan et al. (6) is: HR Wallingford and Cranfield University, UK jointly developed the Water Siulation odel, WaSi (Hess et al., ). WaSi is a one-diensional, daily, soil water balance odel that requires daily reference evapotranspiration and rainfall data. Reference ET is used in WaSi to estiate the changes in the soil water content taking into account inputs of rainfall and irrigation including canal seepage wherever relevant. Daily surface runoff due to rainfall is estiated using US SCS curve nuber technique (USDA, 1969). For the redistribution of soil water, the upper boundary is the soil surface and the lower boundary is an ipereable layer. With WASIM only a one layered soil can be siulated. The soil is divided in five different copartents where water can be stored: Copartent : The surface layer ( -.) Copartent 1: The active root zone (. - root depth) Copartent : The unsaturated copartent below the root-zone (root depth water table) Copartent 3: The saturated copartent above drain-depth (water table drain depth) Copartent 4: The saturated copartent below drain-depth (drain depth ipereable layer) The boundary between the second and third depth increents changes as the roots grow. Before plant roots reach., the second depth increent has zero thickness. Siilarly, the boundary between the third and fourth depth increents fluctuates with the water table depth. Soil water oves downward fro one depth interval to the next only when the soil water content of the upper depth interval exceeds field capacity. In this case, the rate of drainage is a function of the aount of excess water. If the volue water fraction is between the field capacity and saturation then the drainage released fro the copartent is calculated fro an equation proposed by Raes and van Aelst (1985). The deep percolation fors the input Page 1 of 49

11 into a subroutine, which predicts the depth to the water table that includes the ipact of a field drainage syste. Figure 3 Overview of the soil water balance WaSi utilizes the ass balance of salt in a one diensional profile with the sae depth intervals (increents) used for the water balance odel. Respective salt concentrations of the various inputs and outputs are ultiplied with water contents to arrive at the salt contents of soil and drainage water. On the basis of water and salt balances, WaSi predicts surface runoff, evapotranspiration (odified for the crop cover and soil water status), id span water table, drain outflow, soil water content, soil salinity and drainage water quality. The WaSi is user friendly with clear instructions on the operation of the odel provided in the anual written by Hess et al. (). It sees that Wasi is a siple tool to evaluate and design drainage systes. Nevertheless, as this odel is a recent incorporation to the literature it will be appropriated that soe evaluations were done in order to validate it.. The SALTMOD odel SALTMOD is a coputer progra for the prediction of salinity of soil oisture, ground water and drainage water developed by R.J. Oosterbaan and Isabel Pedroso de Lia at ILRI (International Institute for Land Reclaation and Iproveent). With the SALTMOD odel it is possible to study the evolution of salinity, depth of water table and the drain discharge. The general principles of SALTMOD and the assuptions based on which the odel was developed as given in Oosterbaan () are: Page 11 of 49

12 Seasonal approach The odel is based on seasonal water balances of agricultural lands. Four seasons in one year can be distinguished. The nuber of seasons can be chosen between a iniu of one and a axiu of four. The duration of each season is given in nuber of onths. Seasonal tie step is considered in the coputation ethod depending upon the specific situation of the study site. Hydrological data The odel uses seasonal water balance coponents as input data. These are related to the surface hydrology (e.g. rainfall, evaporation, irrigation, use of drain and well water for irrigation, runoff) and the aquifer hydrology (e.g. upward seepage, natural drainage, groundwater puping). The other water balance coponents (e.g. downward percolation, upward capillary rise, subsurface drainage) are predicted as output. Soil strata SALTMOD accepts four different reservoirs naely (i) surface reservoir above the soil surface, (ii) upper shallow soil reservoir or root zone, (iii) an interediate soil reservoir or transition zone and (iv) deep reservoir or aquifer. If a horizontal subsurface drainage syste is present, this ust be placed in the transition zone, which is then divided into two parts: an upper transition zone (above drain level) and a lower transition zone (below drain level). Water balances The water balances are calculated for each reservoir separately. The excess water leaving one reservoir is converted into incoing water for the next reservoir. The three soil reservoirs can be assigned different thicknesses and storage coefficients, to be given as input data. The depth to water table, calculated fro the water balances, is assued to be the sae for the whole area. Salt balances The salt balances are calculated for each reservoir separately. They are based on their water balances, using the salt concentrations of the incoing and outgoing water. The initial salt concentrations of water in the different soil reservoirs, in the irrigation water and in the incoing groundwater fro the deep aquifer are required as input to the odel. Salt concentration of outgoing water (either fro one reservoir into the other or by subsurface drainage) is coputed on the basis of salt balances, using different leaching or salt ixing efficiencies. Output data The output of SALTMOD is given for each season of any year during any nuber of years, as specified with the input data. The output data coprise hydrological and salinity aspects. The data are filled in the for of tables that can be inspected directly or further analysed with spreadsheet progras. The Page 1 of 49

13 progra offers the possibility to develop a ultitude of relations between varied input data, resulting outputs and tie. According to Oosterbaan (1998), SALTMOD has the following advantages in front of daily water balances progras: It is very difficult to collect daily data, The odel is designed to ake long-ter siulations, Because of high variability in daily data, long-ter siulations are ore reliable than short-ter siulations. Another advantage of SALTMOD is that the data needed to run the odel is easily available or it can be easured with relative ease. Page 13 of 49

14 3 Study of salinity with WASIM As it is said before, the ais of this thesis are fro one hand, to study the salinity evolution in the irrigation syste and by the other hand, consider different possibilities of soil reclaation. In this section, these objectives have been studied with the WASIM odel. First of all, a study of salinity at sall scale is done by reproducing a reclaation experient carried out in the irrigation syste. Here, the calibration of the odel has been done. Later, several possibilities of soil reclaation have been considered. 3.1 Evolution of salinity at sall scale Reclaation experient executed in the Pilot Area of Drainage and Soil Reclaation at INTA-EEASE In Rio Dulce Irrigation Syste, a Pilot Area of Drainage and Soil Reclaation of San Isidro at INTA-EEASE was created with the ai of recovering its saline soils. In this area, several experients were carried out in order to study salinity and its properties. Picture 1 Main entrance to San Isidro Pilot Area of drainage Source: MW Ertsen Picture San Isidro Pilot Area Source: MW Ertsen One of this experients was executed in field 6 (.5 ha) of the entioned pilot area. The area has artificial drainage by eans of two pipe-drains, apart at a ean depth of 19 c. Six irrigations of each one were applied with a ean frequency of 17 days. This experient was done in winter, beginning in May of 1991, which is the dry season in the area. Soils in the area are classified as Ustorthent Tipico, they are fored ostly fro loessical silt with scarce developent with their profiles being Page 14 of 49

15 characterized by A-AC-C horizons. In the first 5 c there is a oderate content of organic atter, even thought it decreases with depth. Figure 4 Pilot Area of Drainage and Soil Reclaation at INTA-EEASE The soils in the area are saline-sodic. Salinity and also cationic exchange capacity vary all over the area. Initial average salinity of the soil is.8 ds/ and the initial average cationic exchange capacity is 6.3, with Ca as the ost coon cation adsorbed. Vegetation is scant and it is coposed ostly by sall brushes. Salinity levels were easured in thirteen plots and at several depths during the experient. It was seen that thanks to irrigations, soil reclaation was effective. Even thought, since the 4 th irrigation, resalinization occurred at the center of the field due to a high water table level. Here, the water table level rose the first eter below surface because the drainage syste was not able to aintain water table level below 1.4 depth. The evolution of salinity with the different irrigations at the center of the field (plot D4) is shown in the following graph. Salinity levels in area D ds/ Initial 1st irrigation nd irrigation 3rd irrigation 4th irrigation 5th irrigation 6th irrigation depth, c Graph Evolution of easured salinity levels at the centre of the field, plot D4 Page of 49

16 3.1. Using the WASIM odel to study and odel reclaation experient at Lote 6 Firstly all the inputs needed by WASIM have been studied: those that are known and those that ust be calibrated. Later, the calibration of the unknown paraeters has been carried out Study of required inputs Soil data The type of soil ust be defined, therefore in WASIM is necessary to introduce the next values: Percentage water at saturation, θ sat Percentage water at field capacity, θ FC Percentage water at peranent wilting point, θ WP Drainage constant, τ Leaching efficiency Saturated hydraulic conductivity, Ksat Curve Nuber In the WASIM database it is possible to select different soils types with default values that can be changed and saved. The soil in Lote 6 has been classified as Ustorthent Típico, this soil is closely siilar to those defined in the WASIM database as Silt Loa and Sandy Loa. Soe soil properties of Ustorthent Típico are known fro the experient called: Deterinación de propiedades físicas en el Área Piloto de San Javier, provincia de Santiago del Estero, (Physics properties deterination in the Pilot Area of San Javier, in Santiago del Estero). In this experient, the bulk density, characteristic hydraulic curve and infiltration rate were deterined. The percentage of water at field capacity and the percentage of water at peranent wilting point can be estiated fro the characteristic hydraulic curve. According to Seda & Rycroft (1983) field capacity is reached after a watering of the soil with a oisture content corresponding to values of pf between. and.5. In the sae way, the wilting point occurs when the suction has risen to - at (pf = 4.). Characteristic Hydraulic Curve pf A AC Table 7 Characteristic curve for the soil Ustorthent Tipico Page 16 of 49

17 Also, in the experient called Ensayo de icrolavado de sales, soil was taken fro a plot in Lote 6 in San Isidro to be analyzed according to its physical and cheical properties. Saturation percentage of the soil was calculated. The percentage of water at saturation can be approxiated by the porosity of the soil calculated with the values of saturation percentage and bulk density. HORIZON Ustorthent típico Saturation Percentage Bulk Density Porosity A AC C C C Mean Table 8 Values of the saturation percentage, bulk density (kg/ ) and porosity for Ustorthent Tipico. Taking this into account, the adopted soil paraeters values are: Percentage water at saturation, θ sat =.458 Percentage water at field capacity, θ FC =.6 Percentage water at peranent wilting point, θ WP =.1 Other soil paraeters need to be deterined by running the odel. The default values that WASIM database gives for those soils that are the closest to soil in Lote 6 are shown in table 9. These default data were used as starting point for odeling the experient. The saturated hydraulic conductivity, leaching and drainage constant have to be calibrated. The curve nuber is not iportant in this case, because it is related with surface runoff that doesn t take place in Lote 6 experient. Ksat Curve τ (/day) Nuber Leaching Sandy loa % Silt loa % Crops Table 9 Default data for the WASIM odel The next step in WASIM is to introduce the surface conditions (type of crops). With WASIM is possible to distinguish between crop cover, ulch and bare soil. Soe inforation is required about the type of crop: cover, root depth, ponding and also, soe transpiration factors like the fraction of total available water (θ FC - θ WP ) that is easily available, expressed as p. Page 17 of 49

18 Figure 5 Crop data entry for (Wasi) In Lote 6, vegetation is scarce and it is fored by sall plants and brushes, there is not a specific crop. To siulate this situation in WASIM a hypothetical crop has been created with a constant depth of 5 c which is the depth where the aount of organic atter is iportant. This theoretical crop is covering 1 % of the area. The P factor is unknown and it ust be calibrated. Drainage In WASIM, drainage fro copartent to copartent is calculated fro: ( θ θ FC ) ( θsat θ FC ) q = τ ( θ θ FC ) ( e 1) /( e 1) *1 / In which q drainage fro copartent to copartent, τ drainage constant, θ volue water fraction, θ FC volue water fraction at field capacity θ PWP volue water fraction at peranent wilting point Volue water fractions at field capacity and at peranent wilting point are already known. The drainage constant is the only paraeter to calibrate. Page 18 of 49

19 Cliate data & irrigation Also, to run the odel, data about potential evapotranspiration, gross rainfall and irrigation are needed. Potential evapotranspiration is obtained fro Lieveld (5), and irrigation data is known fro the experient. Rainfall is not considered during all the siulation since the experient was done in winter, the dry season. Initial salinity values and water content Finally, is necessary to introduce soe data about the initial water content, initial water table depth below surface and initial salinity in each of the copartents. The initial water content and the water table depth below surface have to be calibrated. The initial salinity is known Calibration As it has said before, soe paraeters need to be calibrated to reproduce the experient as it was done. Drainage constant, t Initial water content & depth P, fraction of easily available water Leaching efficiency Saturated hydraulic conductivity, Ksat At the sae tie, these paraeters are influencing diverse processes. In this section, all these processes are studied in order to calibrate all the paraeters related with the. Drainage Water table depth Capillary rise Actual ET Salinity Drainage Drainage constant τ is the only paraeter related with drainage that reains unknown. To study its influence on the drainage, several trials have been done with different values of this paraeter: τ =.55, τ =.37, τ =.17. Default values are taken for the other paraeters. In the sae way, the initial water table level is taken at 3 eters depth. Initial water content is studied at field capacity and at peranent wilting point for all the copartents. Page 19 of 49

20 In the next graphs it can be seen that in the evolution of the water table depth, the influence of the drainage constant is insignificant copared to the others paraeters like the initial water content. Therefore, to siulate Lote 6 experient, the default database WASIM value was used as drainage constant. Water table level Initial conditions at FC Water table level Initial conditions at PWP 1/5/1991 8/5/1991 /5/1991 /5/1991 9/5/1991 5/6/1991 1/6/ /6/1991 6/6/1991 3/7/1991 1/7/ /7/1991 4/7/ /7/1991 1/5/1991 8/5/1991 /5/1991 /5/1991 9/5/1991 5/6/1991 1/6/ /6/1991 6/6/1991 3/7/1991 1/7/ /7/1991 4/7/ /7/ t =.55 t =.37 t=.17 t=.55 t=.37 t=.17 Graph 3 Evolution of water table level with initial conditions at FC and different values of τ Water table depth Graph 4 Evolution of water table level with initial conditions at PWP and different values of τ The paraeters related with the water table depth are the initial water content of the different copartents of the soil and the initial water table depth. As the experient was carried out in the dry season, it can be assued that the water content in the top-soil copartent was at peranent wilting point. Siilarly, in the unsaturated zone the water content is supposed to be at field capacity because in this copartent water is not extracted due to transpiration of plants and this is the point where no drainage takes place. Taking these arguents into account, initial water content in the root zone is presued to be between field capacity and peranent wilting point. An average value between peranent wilting point and field capacity is chosen. The next step is to select the initial water table depth. Several tries have been done with different initial water table depths. To select the correct one, it ust be taken into account that in the experient resalinization took place after the 4 th irrigation because the water table raised to 1.4 depth. Moreover, in the 5 th and 6 th irrigations the water table depth reached the first eter. The results fro graph 5 show that the initial water table depth should reain between 3.5 and 4 eters. Page of 49

21 Water table depth Initial water table depth 3 Initial water table depth 3.5 Initial water table depth 4 1/5/91 8/5/91 /5/91 /5/91 9/5/91 5/6/91 1/6/91 19/6/91 6/6/91 3/7/91 1/7/91 17/7/91 4/7/91 31/7/91 Graph 5 Evolution of the water table depth with different initial water table levels. Default values are used for those values that reain unknown Capillary rise & actual evapotranspiration Actual evapotranspiration depends on the aount of water that is available in the upper layer of the soil (root zone) and on the capillary rise. WASIM takes water fro the saturated zone when no water is available in the upper part of the soil. In the experient resalinization took place since 4 th irrigation, due to capillary rise. So, if capillary rise occurred is because not enough water was easily available in the root zone. P is the fraction of total available water that is easily available. The higher the p factor is, the larger the aount of easily available water is. In graph 6 it is shown the actual ET for different values of p, for the first 47 days of the experient (starting at 1 st of May). The saturated hydraulic conductivity is taken equal to.6 /day (default value in WASIM). The water table level is low enough to avoid capillary rise, so the effect of p can be studied without any interference. With values of p higher than p =.3, plants transpire at its potential rate. With a value of p equal to zero, this is not possible. There is not enough easily available water stored in the root zone between field capacity and peranent wilting point. As capillary rise only happens when there is no easily available water in the root zone, p ust be equal to zero. Page 1 of 49

22 Actual ET days p= p=.3 p=1 Graph 6 Actual ET for different values of p factor Once the value of p has been set, the next step is to study capillary rise carefully. In WASIM, capillary rise depends of the water table level, root depth and saturated hydraulic conductivity. In the graphs below, capillary rise is plotted for different values of saturated hydraulic conductivity. In the left one, actual ET for different values of saturated hydraulic conductivity is calculated with WASIM for a p value equal to zero. In this case, the water table depth is shallow enough to allow capillary rise. The right graph shows the aount of capillary rise that these situations produce. With a lower value of Ksat, capillary rise is higher as is actual ET. The range of values of saturated hydraulic conductivity for the kind of soil in Lote 6 fluctuates fro. to.6 /day (Wasi database). Actual ET Capillary Rise /day ET k=.6 ET k=.3 ET k= /day Capillary Rise, k=.6 Capillary Rise, k=.3 Capillary Rise, k= Graph 7 Actual ET for different values of saturated hydraulic conductivity. Graph 8 Capillary rise for different values of saturated hydraulic conductivity. Page of 49

23 Suary By now, ost of the paraeters have been calibrated or they have been placed in an accurate interval of values. Only the leaching efficiency reains copletely unknown. This paraeter will be calibrated with the study of salinity Salinity Drainage constant Unsaturated hydraulic conductivity; Ksat Initial Water Table level Fraction of easily available water; p τ = /day Table 1 Suary of calibrated paraeters The evolution of salinity can be studied in ore detail. The paraeters and processes that are connected with salinity are the next: - Leaching - Capillary rise Saturated hydraulic conductivity - Water table level Initial water table level In order to find those values of each paraeter that best represent the salinity behavior in the experient, several trials have been done with different values of leaching efficiency, unsaturated hydraulic conductivity (capillary rise) and initial water table depth. Leaching Different values of the leaching efficiency have been used in the WASIM odel for an initial water table level of 4 eters and a saturated hydraulic conductivity of.6 eters per day. The results are shown in graph 9. In the upper graph the evolution of salinity in the top-soil is shown. The values that the WASIM odel presents are quite different fro the easured ones. Moreover, these values do not change with the leaching efficiency. In the iddle graph, the evolution of salinity in the root zone is shown. In this case, the salinity values vary with the leaching efficiency. Moreover, for soe leaching efficiency values (7 8 %) the evolution of salinity that WASIM gives is approxiate to the easured one in the experient. However, there is no resalinization. This is because the water table level is too deep and capillary rise can not take place. So, a shallower initial water table depth has to be chosen. Page 3 of 49

24 In the lower graph, it can be seen how salinity behaves in the unsaturated zone. In this case, although salinity values change with the leaching efficiency, they do not reproduce the real values at all. 3.5 Top soil ds/ Leaching 9% Experient Leaching 8% Leaching 7% Leaching 5% Initial 16/5/1991 1/6/ /6/1991 3/7/ /7/ /7/1991 Root-zone ds/ Leaching 9% Leaching 8% Leaching 7% Leaching 5% Experient.5 Initial 16/5/1991 1/6/ /6/1991 3/7/ /7/ /7/1991 Unsaturated zone ds/ Leaching 9% Leaching 8% Leaching 7% Leaching 5% Experient.5 Initial 16/5/1991 1/6/ /6/1991 3/7/ /7/ /7/1991 Graph 9: Salinity values after each irrigation in the top-soil, root zone and unsaturated zone, respectively, for different leaching efficiencies values. Page 4 of 49

25 Saturated hydraulic conductivity: In the graph 1 the evolution of salinity with different saturated hydraulic conductivity is shown. Only when resalinization takes place there are iportant differences between the. Top soil ds/ K =.6 /day K =. /day Experient.5 Initial 16/5/1991 1/6/ /6/1991 3/7/ /7/ /7/1991 Root-zone ds/ K =.6 /day K =. /day Experient.5 Initial 16/5/1991 1/6/ /6/1991 3/7/ /7/ /7/1991 Unsaturated zone ds/ K =.6 /day K =. /day Experient 1.5 Initial 16/5/1991 1/6/ /6/1991 3/7/ /7/ /7/1991 Graph 1 Salinity values after irrigate in the top-soil, root zone and unsaturated zone, respectively, for different saturated hydraulic conductivities. Page 5 of 49

26 Initial water table depth: An initial water table depth of 3.5 eters is too high because with an unsaturated hydraulic conductivity of. /day, there is ponding since the 6 th irrigation (see graph 1). Therefore, an initial water table depth of 3.7 eters is chosen. Top soil ds/ Initial watertable depth 3.5 Experient Initial watertable depth 3.7 Initial watertable depth 4.5 Initial 16/5/1991 1/6/ /6/1991 3/7/ /7/ /7/1991 Root-zone ds/ Initial watertable depth 3.5 Initial watertable depth 3.7 Initial watertable depth 4 Experient 1.5 Initial 16/5/1991 1/6/ /6/1991 3/7/ /7/ /7/1991 Unsaturated zone ds/ Initial watertable depth 3.5 Initial watertable depth 3.7 Initial watertable depth 4 Experient 1.5 Initial 16/5/1991 1/6/ /6/1991 3/7/ /7/ /7/1991 Graph 11 Salinity values after irrigate in the top-soil, root zone and unsaturated zone, respectively, for different initial water table depths Page 6 of 49

27 Water table depth ds/.5 Initial watertable depth 3.5 Initial watertable depth 3.7 Initial watertable depth Graph 1 Evolution of water table level with different initial water table depths for an unsaturated hydraulic conductivity of. /day Finally, the calibrated values in this section are: Unsaturated hydraulic conductivity; Ksat Initial Water Table level Leaching efficiency. /day % Table 11 Calibrated values Conclusions Fro the results obtained in the experient and the siulation done in WASIM it can be concluded that the odel is able to siulate the evolution of the water table depth and the salinity in the root-zone, with leaching of salinity and resalinization since the 4 th irrigation. On the contrary, the values of salinity that WASIM offers for the topsoil and the unsaturated copartent don t reproduce those that were easured in the experient. In general, the odel is a good approxiation of the syste and it can help to understand how it works. Taking into account the experient results and the outcoes of the odel, the soil reclaation is possible in the irrigation syste. The WASIM odel is a useful tool to find the optial irrigation schedule and drainage syste that allow reclaation of the soil. Page 7 of 49

28 3. Possibilities of soil reclaation in PRD In this section different options to reove salts fro the soils of Proyecto Rio Dulce irrigation syste have been considered. The ain purpose of this section is not to find a definite solution for salinity in the Rio Dulce irrigation syste but to test how the syste behaves in front of different actions. First of all, the effects that install a drainage syste have in the irrigation schee have been studied. Therefore, different drain depths (1.8, &. ) and different spacing between drains (1, & ) have been tested. These values have been selected since are siilar to those used in the Lote 6 reclaation experient. Also, how salinity behaves at the non-irrigated fields when an irrigation schedule is applied has been studied. The irrigation schedules considered have been: the official irrigation schedule and actual irrigation in Case 3 (paragraph 1.., table 6). All these scenarios have been tested with the WASIM odel. Picture 3 Actual drain in Rio Dulce Irrigation Syste As it is well known, soe inputs are required in the WASIM odel. Those paraeters calibrated in the section 3.1 for the experient in Lote 6 have been used. Likewise, the data of Case 3 related to salinity has been used in all the scenarios (paragraph 1.., table 4). Inputs WASIM Soil data for the WASIM odel Soil type Sandy loa Saturation (%) 45.8 Field capacity (%) 6 Peranent wilting point (%) 1 Drainage coefficient(/day).37 Hydraulic conductivity (/day). Curve nuber for runoff calculations 67 Leaching efficiency (%) 7 Initial salinity CASE 3 Non-irrigated field (ds/) 16.7 Irrigated field (ds/) 1 Table 1 Soil data and initial salinity content for the WASIM odel calibrated in section 3.1 Page 8 of 49

29 Also, daily inputs of cliatic data are required: inforation about potential ET is available at Lieveld (5). Daily rainfall data is available for the year 5 ( while onthly data is known for a period of years (INTA-EEASE). Using as a pattern the events in the year 5, a daily rainfall series has been created. In the next paragraphs the evolution of salinity, the water table depth and the drain flow according to WASIM results with different scenarios are explained Salinity In this part, the evolution of salinity is studied through three different scenarios of irrigation and with a drainage syste installed: Drainage without irrigation at the non-irrigated field Irrigation case 3 at the non-irrigated field. Official schedule at the non-irrigated field After a siulation with WASIM for the three scenarios studied, with different drain depths and spacing between the, the values of salinity reached are shown in the table 13. Those values that are suitable for agricultural use are rearked in the table. It can be seen how only when the fields are irrigated it is possible to achieve suitable values. Salinity decreases with a deeper drain and a saller spacing drain depth. drain depth drain depth 1.8 s=1 s= s= s=1 s= s= s=1 s= s= No irrigation Case Official Schedule Table 13 Salinity values (ECe) after years of siulation for Case 3 But not only is iportant that the syste could reach suitable salinity values for agricultural use. But also, the tie needed to reach these values is iportant. This tie is shown in the table 14. In ost of the cases, the tie needed for the syste to reclaate the soil is too high to be econoically viable. drain depth. drain depth drain depth 1.8 s=1 s= s= s=1 s= s= s=1 s= s= Case Official Schedule Table 14 Years needed by the syste to reach suitable salinity values In the graph 13 the evolution of salinity in the top soil and the root zone of the three scenarios studied are shown (for a depth drain of. eters and a distance between drains of 1 eters). Page 9 of 49

30 In all the scenarios, it can be noticed salinity changes in the soil not only along the years but also during the year (in a onthly scale). This gives away the iportance that the oent when the easures are done has. Moreover, the fact that inputs are not constant during the siulation contributes to obtain ore realistic outcoes. In the case where no irrigation is applied, salinity levels don not decrease during the siulation. The WASIM odel confirs the fact that the installation of drains without an increase of the leaching is useless. In addition, the top soil shows a large variation in the salinity content between the dry and the wet season. Ece Top-Soil d=. & s=1 non-irrigation Ece Root zone d=. & s=1 non-irrigation ds/ ds/ Jan-81 Jan-83 Jan-85 Jan-87 Jan-89 Jan-91 Jan-93 Jan-95 Jan-97 Jan-99 Jan-1 Jan-3 Jan-81 Jan-83 Jan-85 Jan-87 Jan-89 Jan-91 Jan-93 Jan-95 Jan-97 Jan-99 Jan-1 Jan-3 Ece Top-Soil d=. & s=1 Case 3 Ece Root zone d=. & s=1 Case ds/ ds/ Jan-81 Jan-83 Jan-85 Jan-87 Jan-89 Jan-91 Jan-93 Jan-95 Jan-97 Jan-99 Jan-1 Jan-3 Jan-81 Jan-83 Jan-85 Jan-87 Jan-89 Jan-91 Jan-93 Jan-95 Jan-97 Jan-99 Jan-1 Jan-3 Ece Top-Soil d=. & s=1 Official Schedule Ece Root-zone d=. & s=1 Official Schedule ds/ ds/ Jan-81 Jan-83 Jan-85 Jan-87 Jan-89 Jan-91 Jan-93 Jan-95 Jan-81 Jan-83 Jan-85 Jan-87 Jan-89 Jan-91 Jan-93 Jan-95 Jan-97 Jan-99 Jan-1 Jan-3 Jan-97 Jan-99 Jan-1 Jan-3 Graph 13 evolution of salinity levels at non-irrigated fields in Case 3 without irrigation (a), with irrigation case 3(b) and with the official irrigation schedule (c). Page 3 of 49

31 Looking at the cases where irrigation is applied, it can be seen how salinity levels decrease along the siulation reaching in soe years suitable salinity values for agricultural use. In general, the topsoil copartent suffers ore draatic variations in its salinity during the year copared to the root zone copartent. This is because the top soil copartent is directly exposed to the cliatic events. In the irrigated scenarios, the evolution of the root zone and the topsoil copartents is siilar whereas in the case where no irrigation is applied the behavior of both copartents is totally different. If irrigation is considered without a drainage syste, then the salinity levels continue being high due to capillary rise during the dry seasons. The results of the siulation can be seen in the graph 14. As a conclusion it can be said that the application of irrigation without the appropriate drainage is useless. Ece Top-Soil no drainage Ece root zone no drainage ds/ Jan-81 Jan-83 ds/ Jan-85 Jan-87 Jan-89 Jan-91 Jan-93 Jan-95 Jan-97 Jan-99 Jan-1 Jan Jan-81 Jan-83 Jan-85 Jan-87 Jan-89 Jan-91 Jan-93 Jan-95 Jan-97 Jan-99 Jan-1 Jan-3 Graph 14 evolution of salinity levels at non-irrigated fields in Case 3 without drainage 3.. Water table level In the next table the average water table levels registered during the siulation for each case is given. Also, graph represents the evolution of the water table level for the three cases studied, specifically for a drain depth of. and a spacing of 1 eters. drain depth 1.8 drain depth drain depth. s=1 s= s= s=1 s= s= s=1 s= s= Official schedule Case No irrigation Table Water table depth, in, after years of siulation for Case 3 When the field is irrigated, the water table level increases considerably because the drainage syste can not drain the entire overflow. It is possible that bigger drains work properly, but this has not been tested in this thesis. Page 31 of 49

32 If the two irrigation schedules are copared, it can be seen that with the official irrigation schedule the water table depth is lightly shallower than with the case 3 irrigation schedule. When no irrigation is applied, the water table level reains around.5 eters depth where the drainage syste is not effective. Although the water table level reains around 1.5 eters depth during all the siulation, the water table levels vary every year because the inputs are variable. Water table depth d=. & s= Jan-81 Jan-8 Jan-83 Jan-84 Jan-85 Jan-86 Jan-87 Jan-88 Jan-89 Jan-9 Jan-91 Jan-9 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan- Jan-1 Jan- Jan-3 Jan-4 Case 3 Official Schedule Non-irrigated Graph Water table levels for a drain depth of. and a spacing of Drain flow If the total aount of flow that the drains evacuate during all the siulation is copared, it can be seen that the drain flow with the official irrigation schedule is higher than the drain flow with the case 3 irrigation schedule. This indicates that WASIM takes into account the total aount of irrigation and also, the distribution of this irrigation along the year. The aount of irrigation per year is siilar in both cases but not the distribution of this irrigation ((paragraph 1.., table 6). s=1 drain depth drain depth. drain depth 1.8 s= s= s=1 s= s= s=1 s= s= Official Schedule Case Table 16 Drain flow after years of siulation for Case Conclusions It is possible to reach suitable salinity levels for agriculture whit the installation of a drainage syste and the irrigation of the fields. Nevertheless, the schedule and the total aount of irrigation have to be studied in ore detail. In the sae way, the drainage syste has to be tested ore exhaustively. Page 3 of 49

33 4 Study of salinity with SALTMOD Like in the last section, here the ain purposes are to study the salinity process and the possibilities of soil reclaation of the fields in Rio Dulce Irrigation Syste. In this case, the odel used is SALTMOD. In the first part, the objective is to study the evolution of salinity in the PRD over a larger period of several years. This is done with two purposes: first, to see if SALTMOD can siulate the salinity levels easured on the fields and second to study these easures. In the second part, several possibilities of soil reclaation have been considered. 4.1 Study of salinity in the PRD at larger scale Most of the data that is needed to study salinity fro the Rio Dulce irrigation syste are already known (see paragraph 1..). Nevertheless, soe paraeters reain unknown and ust be calibrated. Once this calibration has been done, different scenarios have been studied Calibration To carry out the calibration of the unknown paraeters, CASE 1 has been used as it is the one with ore data available. Starting with low salinity values, the objective is to reach after several years the easured values in CASE 1 in Río Dulce Irrigation Syste. The Rio Dulce irrigation syste is characterized by having irrigated and non-irrigated fields within the coand area. Within SALTMOD two fields were siulated: one irrigated and one non-irrigated. To ipleent a SALTMOD input file, it is necessary to define inforation about hydrological data, irrigation schedules, soil properties, area, initial salinity values As the odel calculates a seasonal water balance, the values of irrigation and hydrological data have to be introduced per season. In this case, there are two seasons: one dry (fro May to October) and another wet (Noveber to April). Initial salinity values used in SALTMOD are expressed as the EC of the soil oisture when saturated under field conditions. Data related to salinity, irrigation schedules and hydrological data is obtained fro Prieto (6) as it can be seen in paragraph 1... As it is known, fro several experients carried out at the Pilot Areas of San Isidro and San Javier, located in Rio Dulce irrigation syste, soe properties of the soil are known. These values were already used for the WASIM odel. Also, with the WASIM odel soe paraeters that are required in SALTMOD, like leaching efficiency, were calibrated. Their values were used also in SALTMOD. All these values are shown in table 17. As the values of precipitation are effective precipitation, runoff is supposed to be equal to zero. Page 33 of 49

34 Suary of input paraeters of SALTMOD 1. Soil properties Fraction of irrigation or rain water stored in root zone UNKNOWN Total porosity of root zone.54 Total porosity of transition zone.46 Total porosity of aquifer (assued).46 Critical depth for capillary rise UNKNOWN Leaching efficiency of root zone 7 % Leaching efficiency of transition zone 7 % Leaching efficiency of aquifer 7 %. Water balance coponents Irrigation in the season Irrigation in the season.391 Rainfall in the season Rainfall in the season.85 Evapotranspiration in the season Evapotranspiration in the season.5958 Incoing groundwater flow through aquifer during the season (assued) Outgoing groundwater flow through aquifer during the season UNKNOWN Surface runoff in the season 3. Drainage criteria and syste paraeters Root zone thickness ().5 Depth of subsurface drains () No drains Thickness of transition zone between root zone and aquifer () 4 Thickness of aquifer, assued () 4 4. Initial and boundary conditions Depth of the water table in the beginning of the season () 4 Initial salt concentration of soil oisture in root zone at field saturation (ds/) 4 Initial salt concentration of the soil oisture in transition zone (ds/) 4 Average salt concentration of incoing groundwater (ds/) 9.6 Average salt concentration of incoing Irrigation water (ds/).8 Table 17 Suary of inputs paraeters for Saltod : eter; d: days; ds: deci-sieens. Page 34 of 49

35 Finally, those paraeters that have to be calibrated are: Fs is the storage fraction of the surface water resources, representing the oisture holding capacity. Go is the outgoing flow through the aquifer Dc is the critical depth for capillary rise Note that SALTMOD uses as salinity easure the EC of the soil oisture when saturated under field conditions, while the data we have fro PRD is ECe, the electric conductivity of an extract of saturated soil paste. Approxiately, it can be assued that EC= ECe. To calibrate the values of the outgoing flow through the aquifer and the critical depth for capillary rise, several trials have been done with different values of these paraeters in order to find that cobination which akes that the water table reains at eters depth (easured level, see paragraph 1..) and the salinity levels reach the easured values for Case 1 (paragraph 1..). The Fs values used in this case are: Fs irrigated field, wet season:.5 Fs irrigated field, dry season:.5 Fs non-irrigated field, wet season:.5 Fs non-irrigated field, dry season: 1 The results for the end of the siulation (4 years) are shown in the next table. It can be seen that it is possible to obtain the easured water table depth with different cobinations of Go and dc. Nevertheless, the salinity value for the non-irrigated field is closer to the easured value with an outgoing flow through the aquifer of.5 per season. So, if Go is fixed to.5 per season, then the critical depth has to be.5. Water table depth () Go= /s Go=.5 /s Go=.1 /s Go= /s Salinity irrigated field (ds/) Go=.5 /s Page 35 of 49 Go=.1 /s Salinity non-irrigated field (ds/) Go= /s Go=.5 /s Go=.1 /s dc= dc= dc= dc= Table 18 depths of water table and salinity values (ds/) for different cobinations of Go and dc. To conclude, the last paraeter unknown is Fs. This is the storage fraction of the surface water resources, representing the oisture holding capacity and is different on each season and on each field. To find the best cobination of values of Fs, several trials have been done with the assuption

36 that no percolation occurs at the non-irrigated field during the dry season. So, Fs NIrrig&dry is equal to one. First of all, the Fs value for the non-irrigated field at the wet season has been calibrated. The evolution of salinity can be seen in graph 16. Finally, a value of Fs=.5 is chosen, since is the one with which closest salinity values to the easured ones are obtained. 35 Salinity non-irrigated land for different values of Fs (non-irrigated land and wet season) a b c Fs I&wet Fs NI&wet Fs I&dry ds/ Fs=.5 Fs=.6 Fs=.4 Fs NI&dry Table 19 Fs values years Graph 16 Evolution of salinity The next step is to calibrate other Fs paraeters. Several cobinations were ade. Of all the studied cobinations, C was chosen. a b c d Salinity non-irrigated land for different values of Fs (irrigated land) Fs I&wet Fs NI&wet Fs I&dry Fs NI&dry Table Fs values ds/ 3 5 a b c d years Graph 17 Evolution of salinity It is possible to reach the easured values in the irrigation syste with the SALTMOD odel. However, it can be noticed that salinity at the non-irrigated Page 36 of 49

37 field increases along the years and is not possible to reach a stable situation. This is because rainfall like the rest of inputs is a constant rate along the years. So, if leaching of salts due to percolation and resalinization due to capillary rise are constant, then salinity increases year by year. As an assuption it is considered that in a real case after years a stable situation would be reached. So, to choose the best cobination the values reached at years of siulation will be considered Different scenarios In this section, different scenarios are considered in order to know how salinity behaves with different irrigation schedules. The procedure is the sae that in the last section: starting with low salinity values, study how salinity evolutions. The paraeters calibrated in Case 1 have been used. Season 1 () Season () Total irrigation () Official Schedule Case Case Case Case Table 1 different irrigation schedules at different areas of PRD In all the scenarios studied salinity has an increasing trend in the nonirrigated fields. This is because all the inputs are invariable during all the siulation. Secondary salinization occurs because there is capillary rise. If salinization in the dry season is larger than the leaching of salts due to percolation in the wet season, salinity level increases. As here this is constant along the years, salinity has a rising tendency. It can be seen as the larger the aount of irrigation is, the higher salinity values are. This is because SALTMOD does a seasonal water balance and does not take into account the distribution of this irrigation along the season and how it affects percolation and capillary rise respectively. As irrigation increases, the water table depth is shallower and consequently, capillary rise increases. As an exaple if Case 3 and Official Schedule are copared the total aount of irrigation per year is siilar but the distribution of this irrigation is copletely different in each case (see table 6, paragraph 1..). Nevertheless, the salinity values reached are quite siilar. In the sae way, the values reached in Case 3 are closer to the easured ones (see table 6, paragraph 1..). The salinity values in Case 4 that SALTMOD gives as an output are different to the easured ones. Page 37 of 49

38 Salinity Non-irrigated land ds/ 5 Official Schedule Case 1 Case Case 3 Case years Graph 18 Evolution of salinity (EC of soil oisture when saturated under field conditions) at non-irrigated fields for a running of years Water table depth Official Schedule Case 1 Case Case 3 Case years Graph 19 Evolution of water table depth Salinity Irrigated Field ds/.5 Official Schedule Case 1 Case Case 3 Case years Graph Evolution of salinity (EC of soil oisture when saturated under field conditions) at irrigated field Page 38 of 49

39 4.1.3 Inputs variables By now, all the calculations ade with SALTMOD have used constant inputs. But SALTMOD also offers the possibility of variable inputs. In this section, Case 1 is studied with rainfall variable data (Monthly values fro INTA-EEASE). In the graph 1 the evolution of salinity in Case 1 with constant inputs and with variable inputs is shown. Although salinity has an increasing trend, in this case it can be observed how this tendency is irregular. The increase or decrease of salts in the soil is variable each year, the opposite of the previous cases. At the sae tie, it can be seen a stabilization of the salinity levels in the last years of the siulation. Nevertheless, the order of agnitude of salinity levels for both siulations is the sae. Salinity non-irrigated field ds/ Input constante Input variable years Conclusions Graph 1 Salinity at the non-irrigated field With SALTMOD is possible to predict how the evolution of salinity in the next years is going to be, but the outputs that SALTMOD presents can diverge considerably with reality. In the siulated cases, after 4 years of siulation salinity continues increasing year by year. This is because all the inputs are invariable during all the siulation. The larger the aount of irrigation is, the higher the salinity values are. This is because SALTMOD does a seasonal water balance and does not take into account the distribution of this irrigation along the season and how it affects to percolation and capillary rise respectively. With the SALTMOD odel is possible to siulate at the sae tie an irrigated and a non-irrigated field which is really suitable for PRD. Page 39 of 49

40 4. Possibilities of soil reclaation in PRD In this section different options to reove salts fro the soils of Proyecto Rio Dulce irrigation syste have been considered with SALTMOD. Like in the part 3., the ain purpose of this section is to test how the syste behaves in front of different actions but not to find a definite solution for salinity. First of all, the effects that install a drainage syste have in the irrigation schee have been studied. Therefore, different drain depths (1.8, &. ) and different spacing between drains (1, & ) have been tested for different cases. Also, how salinity behaves at the non-irrigated fields when an irrigation schedule is applied has been studied (with the drainage syste included). Like in the section 3., the irrigation schedules considered have been: the official irrigation schedule and actual irrigation in Case 3 (paragraph 1.., table 6). Note that with SALTMOD two fields are siulated: one irrigated and the other one not irrigated Drainage Taking as initial inputs the easured values of salinity and the paraeter values calibrated in Case 1, several drain depths and separations between the have been considered for different scenarios (Case 1, Case 3 and Case 4) and for two different irrigation schedules (for the irrigated field): those that in fact are applied and the official irrigation schedule. In the next nubers, the salinity values after years of siulation with SALTMOD are shown. Case 1 Case 3 Case 4 Critical depth () Critical depth () Critical depth () Distance between drains Table Salinity values (EC of soil oisture when saturated under field conditions) after years of siulation for Case 1, Case 3 and Case 4 Case 1 Case 3 Case 4 Critical depth () Critical depth () Critical depth () Distance between drains Table 3 Salinity values (EC of soil oisture when saturated under field conditions) after years of siulation for Case 1, Case 3 and Case 4 with the official irrigation schedule Page 4 of 49

41 In the tables & 3, those values of salinity that are suitable for agricultural use are bold. As can be seen, only with a critical depth of. it is possible to obtain such values. If the results obtained with the official irrigation schedule and those achieved with the existents irrigation schedules are copared, it can be seen that they are quite siilar for cases 3 and 4, but they are copletely different in case 1. This is because the aounts of water irrigated in cases 3 and 4 are closer to the official schedule than in case 1 where the real irrigation is lower. Not only it is iportant to know that suitable salinity values can be reached, but also it is essential to know the tie that the syste needs to reach these values. In this case, it takes a considerable nuber of years to reach lower levels of salinity. Case 1 Case 3 Case 4 Distance between drains Real Official Real Official Real Official Table 4 nuber of years necessaries to reach suitable salinity values for agricultural use. In graph is given the evolution of salinity at the non-irrigated field for two different cases (Case 1 & Case 3). It can be seen how salinity follows a decreasing trend. Every year, resalinization takes place during the dry seasons in a constant rate. In the graph b it can be seen different behaviors of the salinity levels depending on the distance between drains. With a spacing of 1 eters reclaation of the soil is possible. Although salinity levels stop increasing with a spacing of eters, reclaation is not feasible. ds/ Salinity non-irrigated land CASE 1 dc=. s= s= s=1 ds/ Salinity non-irrigated land CASE 3 dc= s= s= s= years years Graph Evolution of salinity at non-irrigated fields Case 1 and Case 3 for a drain depth of. and different separations between the drains Salinization only stops increasing when drains are able to aintain the water table level deep enough to avoid capillary rise. Moreover, reclaation of the soil only takes place when the salts of the upper parts of the soil are leached and drained out of the syste. Page 41 of 49

42 In the next table, water table depths for each case are shown: Case 1 Case 3 Case 4 Critical depth () Critical depth () Critical depth () Distance between drains Table 5 Water table depths, in, after years of siulation for Case 1, Case 3 and Case Drainage & Irrigation Once several possibilities of drainage have been studied to solve salinity probles, in this part the effects of drainage and irrigation at non-irrigated fields have been considered. Starting fro the known situation in case 3 a watering has been applied at the non-irrigated field in order to understand how salinity behaves. In the following nubers, the results fro a siulation with SALTMOD odel during years can be seen. In this siulation, the sae irrigation schedule is applied to both fields (the initial salinity levels are shown in table 4, paragraph 1..). At the sae tie, a drainage syste has been considered and different drain depths and distance between the have been tested. Case 3 Official schedule Critical depth () Critical depth () Distance between drains Table 6 Salinity values (EC of soil oisture when saturated under field conditions) after years of siulation for Case 3 Case 3 Official schedule Critical depth () Critical depth () Distance between drains Table 7 nuber of year necessaries to reach suitable salinity values for agricultural use in each case: 4 ECe (ds/) After years of siulation in SALTMOD, agricultural suitable salinity levels have been reached in all the cases. Here, not only it is iportant to know Page 4 of 49

43 that such values are achieved but also, how any years the syste needs to reach these values. Diverse cobinations allow obtaining the search values in four years which is reasonable. Reclaation of the soil is faster when irrigation is applied in the nonirrigated field. ds/ Salinity non-irrigated land CASE 3 dc=. 9 s= s= s=1 ds/ Salinity non-irrigated land CASE 3 dc=. s= s= s= years years Graph 3 evolution of salinity levels at non-irrigated fields in Case 3 with irrigation (a) and without irrigation (b). Salinity easured as EC of soil oisture when saturated under field conditions Conclusions Fro the outcoes achieved soe points can be concluded: If a drainage syste is installed in the area without irrigation, reclaation is possible with deeper drains and less separation between the. But, the tie needed to reach this situation is not viable. However, if irrigation is also applied, the drains depth can be shallower and the distance between the larger. Moreover, reclaation can be achieved in less tie. Picture 4 Irrigated field in the PRD Page 43 of 49

44 5 Conclusions Once all the calculations have been done, the next conclusions can be obtained: Fro one hand, in the thesis the evolution of salinity has been studied at sall scale with the WASIM odel and at larger scale with the SALTMOD odel. About this part, the following questions can be coe up: Are the results siilar to the easured ones? Can the studied odels siulate what it is happening in reality? In the first section of this part, the Lote 6 experient was reproduced with the WASIM odel. At the sae tie, soe unknown paraeters were calibrated. Picture 5 Canal in the PRD MW Ertsen Looking at the outcoes of the progra, it can be noticed that WASIM progra was able to reproduce not only the evolution of the water table level during the experient but also, the salinity levels in the root zone. Nevertheless, the salinity outcoes that WASIM presented at the top soil and in the unsaturated zone were copletely different fro the easured ones. In the top soil copartent, the WASIM outcoes were independent of the different paraeter values that had to be calibrated. Moreover, the outcoes were always closer to each other and different fro those that were easured in the experient. In the unsaturated zone, although salinity values varied depending on the different values of the paraeters, these were different to those easured in the experient. To conclude it can be said that the odel is a good approxiation of the syste and it can help us to understand how the syste is going to evolution. In the second part of the thesis, the SALTMOD odel has been used to study salinity at larger scale. Two fields have been siulated: one irrigated and the other one without irrigation. Starting with lower salinity values in both fields, Page 44 of 49

45 the ain purpose of this siulation was to know how salinity behaves along the years. According to the SALTMOD outcoes, salinity levels in the irrigated fields were low while salinity increased in the non irrigated field. In this case, salinity had an invariable increasing trend during the tie siulated. This is because the inputs were constant each tie-step. So salinization was constant each year. Obviously, this does not happen in real fields. Finally, it can be concluded that although SALTMOD helps to understand how salinity is going to evolution along the years, the values it gives and the behavior during the siulation are not reliable if constant inputs are used. By the other hand, if a siulation with variable rainfall data is done, it can be seen how salinity in the non irrigated field does not have a constant increasing trend. In this case, salinity changes depending on the inputs and the outcoes are ore realistic. By the other hand, in this thesis several possibilities of soil reclaation in the PRD irrigation syste have been considered. Like in the first part, SALTMOD and WASIM have been used. Regarding this part, what should be answered is: Is it possible to iprove the salinity levels in the non irrigated fields? Are the odels outcoes trustworthy? Picture 6 Salinity in PRD According to the odels is possible to reach suitable salinity levels for agriculture whit the installation of a drainage syste and the irrigation of the fields. Nevertheless, the tie and requisites needed are different in each odel. SALTMOD outcoes are ore favorable than WASIM ones. As an exaple, in the next table it is shown the tie needed by the syste to reach suitable salinity Page 45 of 49