Irrigation
Z. Sojoodi; H. Shokati; Y. Sojoodi; M. Mashal
Abstract
IntroductionThe constructive effects of green spaces on the quality and livability of the urban environment have been reported in many studies. Therefore, using methods that can accurately estimate the evaporation of transpiration in green space can help to reduce water loss. The purpose of estimating ...
Read More
IntroductionThe constructive effects of green spaces on the quality and livability of the urban environment have been reported in many studies. Therefore, using methods that can accurately estimate the evaporation of transpiration in green space can help to reduce water loss. The purpose of estimating water demand for urban green space is also different from the purpose of determining water demand for an agricultural farm. In urban green space, the goal is to maintain good growth, appearance and acceptable plant health, while biomass production is the main goal on agricultural farms. Therefore, urban green space can typically be managed using an irrigation area that is less than the amount of water needed to produce agricultural products. Due to the limited water resources in arid areas, the use of less irrigation in urban green space can be desirable to save water consumption.Materials and MethodsThe Wucols method for estimating Water requirements in green space was developed by Castello et al. (4). They developed the Wucols water taxonomy guidelines for planting green space in California. The Wucols method estimates evapotranspiration in green space using reference evapotranspiration and a set of coefficients (Species factor, density factor and microclimate factor). PF method is the minimum acceptable irrigation for green space plants that emphasizes maintaining the beauty of the plant. In this method, the water required by green space plants is considered as a percentage of ET0 so as not to reduce their appearance and performance. In this approach, PF is a regulatory factor that is actually considered instead of Kc and multiplied by ET0, except that the emphasis is on the appearance of the plant and not on its optimal growth and yield. The IPOS method has been developed by the Government of South Australia for planning and managing water needs in public open spaces, especially sports lawns and amusement parks. In this method, the water requirement of grass in urban open space is calculated. In this method, plant transpiration evaporation (ETL) is calculated by multiplying reference transpiration evaporation factors (ET0) by grass vegetation coefficient (Kc) by plant stress factor (Kst).Results and DiscussionThe results showed that the highest rate of evapotranspiration obtained by Wucols method was 83.38 mm during 21 Jun-21 Jul. Also, the rate of transpiration evaporation during one year of the experimental period was estimated to be 556.5 mm. The results of estimation of transpiration evaporation by PF method also show the maximum amount of transpiration evaporation during 21 Jun-21 Jul and is 75.55 mm. The evapotranspiration rate during one year was estimated to be 505.9 mm. For the Ipos method, the highest rate of transpiration evaporation was estimated to be 36.38 mm during 21 Jun-21 Jul and 242.9 mm during the experimental period. Gross irrigation requirement is estimated by considering 70% irrigation efficiency for each month using all three methods. For the Wucols method, the gross irrigation need during one year was estimated to be 794.8 mm. For the PF method was 722.7 mm and for the IPOS method was 346.9 mm. According to the reported irrigation records for the study area, which is 900 mm per year, the Wucols method has the closest result to the irrigation records.ConclusionThe results showed that the Wucols method has the best and closest estimate according to the irrigation records of the study area. The gross irrigation requirement calculated by the Wucols method during a year is 794.8 mm, which is 12% less than the gross annual irrigation requirement of the studied green space. While PF and IPOS methods determined the amount of gross demand 20 and 62% less than the annual irrigation rate in the region, respectively. The results of this study show that the Wucols method for estimating the water requirement of plants in urban green space where there is a combination of different plant species is more reliable than the PF and IPOS methods due to the diversity of species, vegetation density and different climates.
Khodayar Abdollahi; Somayeh Bayati
Abstract
Introduction: Curve number (CN) is a hydrologic parameter used to predict the direct runoff depth or the excessive rainfall that infiltrates into the soil. This parameter, which indicates surface water retention, is very important in the processes relating to flooding. Vegetation of the region is a major ...
Read More
Introduction: Curve number (CN) is a hydrologic parameter used to predict the direct runoff depth or the excessive rainfall that infiltrates into the soil. This parameter, which indicates surface water retention, is very important in the processes relating to flooding. Vegetation of the region is a major factor affecting peak flow and flood volume. The peak flow is highly influenced by the land surface characteristics, for example at the time that vegetation coverage is naturally low or while vegetated areas are decreasing, the peak discharges increase as well. In this study, the flood hydrograph of Kareh-Bas Basin was simulated using the HEC-HMS model. The simulation was used to estimate the values of the annual curve number in the basin of interest.
Materials and Methods: Model data requirements for this study were temperature, precipitation, and evapotranspiration and discharge time series. The model was calibrated for the period 2000-2010. Then, the model was implemented independently for simulating of rainfall-runoff for each year without any change in the optimized parameters. The model was calibrated only by changing curve number. The average curve number of the basin for each year was computed using the weighted mean method. The MODIS leaf area index raster maps were downloaded from the Modis site. The maps were converted into ASCII format for spatial statistics and calculating the monthly spatial average. The correlation between the curve number and leaf area index was investigated by a nonlinear curve fitting. This lead to the development of a curve number as a function of the vegetation cover for each year. Finally, the accuracy of the developed relationship was investigated using the Nash-Sutcliffe efficiency coefficient by comparing the curve number obtained from the HEC-HMS model and the simulated values from the new relationship.
Results and Discussion: The obtained Nash-Sutcliff coefficient of 0.58 showed that the HEC-HMS model was capable to simulate the flood hydrograph with relatively good accuracy. The sub-basin spatial mean showed that the sub-basins 1 and 2 take the highest curve number values. This indicates that surface water retention in these sub-basins is less than the other sub-basins, which may lead to a sharper hydrological response or flood. In sub-basins 3 and 4, where vegetation density is higher thus land use acts as a predominant factor in hydrologicalbehavior of these sub-basins, the curve number was lower. The study shows the hydrological response depends on the temporal variation of the land cover, for instance in 2010, when the leaf area index increased by a factor of 1.4, the curve number has decreased to 47. As it is predictable with decreasing vegetation the peak discharge and flood volume was increasing. We found a direct nonlinear relationship between basin scale Leaf Area Index and Curve Number with a correlation coefficient of 0.7, indicating that the variation of the curve number is a function of the leaf area index. The developed model allows calculating curve number values based on the remotely sensed leaf area index. This relationship can be used as an auxiliary function for capturing the vegetation changes and dynamics. The accuracy of the derived equation was evaluated in terms of Nash-Sutcliffe's efficiency coefficient. A value of Nash-Sutcliff coefficient of 0.72 showed that this relationship is good enough for calculating basin or sub-basin curve number values capturing the dynamics of leaf area index.
Conclusions: The obtained Nash-Sutcliff efficiency coefficient from HEC-HMS showed that the model was able to simulate the flood hydrograph of Kareh-bas basin with relatively good accuracy. However, the visual interpretation shows there is a weakness in the simulation of the falling limb of the simulated hydrographs. This may be an indication that the drainage of stored water at the basin was not well-simulated by the model. In general, it can be said that peak discharge and flood volume were under-estimated. By increasing the curve number, the peak discharge values also were increasing. The pair data for spatially weighted values for curve number and averaged annual leaf area index showed that an increase in leaf area index leads to a lower value in obtained curve number. This may result in lower peak discharge and volume of the flood. Such relationships may be taken as a measure for flood control. Meanwhile remotely sensed leaf area index products may be considered as an opportunity to capture the dynamics of the land cover.
abdolmajid liaghat; masoud Pourgholam amiji; pourya mashhouri nejad
Abstract
Introduction: With due attention to the limitation of water resources in Iran and specific geographical conditions of the country, using modern methods of irrigation with low water usage is inevitable. By applying suitable management in water system, soil and plant, while increasing product, we can establish ...
Read More
Introduction: With due attention to the limitation of water resources in Iran and specific geographical conditions of the country, using modern methods of irrigation with low water usage is inevitable. By applying suitable management in water system, soil and plant, while increasing product, we can establish a sustainable agriculture. Today, subsurface irrigation systems are used in various methods around the world, especially in the countries encountering water shortage. One of the newest methods is applying sponge plastic pipes such as tuporex which is installed in the area of plant root. Then, water with the pressure of 0/6-2 atmosphere flows inside it and by exuding, it dampens the area.
Materials and Method: For this purpose, in this study number of 12 concrete lysimeters with the dimension of 2×2×1/25 m was used to investigate the effect of vegetation (mulch) on the efficiency of water consumption and product function for corn, salt accumulation as well as the amount of nitrate wash on soil profile under two permeable subsurface irrigation and surface irrigation. For irrigation, a body of water with salinity of 4 ds/m was used. The plan includes two main treatments (permeable subsurface and surface irrigation) and two sub-treatments (mulch and without mulch) withfactorial experiment in a randomized complete block design with three replications at the College of Agriculture Research Campus, Tehran Universityof technology Located in Karaj, Iran in 2010. Surface irrigation was performed based on the moisturein the soil and permeable subsurface irrigation was performed per dayas much water as was consumed.. Lysimeters soil is prepared from farm soil and through examination, its appearance special weight was registered to be 1.4 gr per cm3 equals to 1400 kg per m3. The amount of nitrogen fertilizer (Urea) was applied on the lysimeters according to the region convention, was 300 kg per hectare (120 gram per each lysimeter(. A half of this amount was used at the time of cultivation and another half was used for the plant 60 days after cultivation; because the amount of water given in this type of system is higher.On the other hand due to the lack of vegetation, the significant amount of evaporated water and water productivity have decreased.
Results and Discussion: Results disclosed that the subsurface irrigation system has important effect in decreasing consumed water (58% with mulch and 40% without mulch) and increasing crop yield (46% in seed corn yield, 50% in forge yield and 12% in weight of one thousands seed corn) in comparison with the surface irrigation system. As well as the subsurface irrigation has prevented lower soil layer from contamination and being salty by decrease salt and nitrate leaching. Besidespresence of mulch in lysimeterhas shown important role in decreasing water consumption and seed corn yield. The important thing is that the highest yield in two type of performance, was recorded in subsurface irrigation treatment with mulch (TM) and this subject is so important when we remind that (TM) treatment had the least amount of water uses. Itmeans that with the least amount of water consumed the highest amount of product was obtained among the treatments.On the other hand, surface and non-mulching (SO) irrigation is expected to have the lowest yield per unit water consumption.
Conclusions: Also in both subsurface irrigation with preamble tube and surface irrigation system, existence of mulch caused to decrease salt concentration to 40% and 30% in soil surface respectively which makes it suitable for the areas facing water shortage. It can be concluded that, existence of mulches in the both subsurface irrigation with permeable tube and surface irrigation system causing water saving 13 and 23 percent, respectively and the rate of saving water in surface irrigation system with presence of mulch has also increased. Thus, it is recommended that some of the plant residuals, like mulch remain on the ground after harvest. The subsurface irrigation with permeable tube system has been prevented from washing nitrate to the depths of the soil. As a result, the environmental pollution caused by nitrate losses in this system is minimal and this system saves fertilizer. Also the concentration of salt solution in the soil profile in subsurface irrigation system was significantly lower than the salt concentration in surface irrigation. As a result in areas that use the saline water for irrigation, the subsurface irrigation with preamble tube confirm better function than surface irrigation system and use mulch can increase yield and reduce leaching.
Ali Reza Vaezi; Mohammad Abbasi; Jalal Heidari
Abstract
Introduction Soil infiltration rate is the major soil hydraulic property which can be affected by the soil physical characteristics and management practices. The use of land can affect various soil properties such as physical and hydraulic properties. Differences of the hydraulic soil characteristics ...
Read More
Introduction Soil infiltration rate is the major soil hydraulic property which can be affected by the soil physical characteristics and management practices. The use of land can affect various soil properties such as physical and hydraulic properties. Differences of the hydraulic soil characteristics such as infiltration rate in various land uses can affect their potential to runoff production as well as soil loss in the catchment. The knowledge of the physical and hydraulic characteristics of various land uses can help to better management of soil and water in the catchment. It is very essential in the semi-arid catchments where vegetation cover is generally poor, the soils are often instable against erosive factors especially when the rainfalls are consecutive and intensive. Therefore, this study was conducted to investigate the soil physical and hydraulic characteristics in the TahamChai catchment, in a semi-arid region, NW Zanjan. Various land uses consist of pastures, rainfed and irrigated lands can be observed in the catchment, which cover about 62%, 33%, and 5% of the catchment area, respectively. The pastures have been covered with poor vegetation and are intensively exhausted by over-grazing. Rainfed lands are mostly under winter wheat cultivation. Soil erosion and sedimentation were the major environmental problem in this catchment.
Materials and Methods The maps of land use and slope gradient were provided for study area. A total of 20 sites were selected based on the surface area of each land use in the catchment located between 34 46-36 53 N latitudes and 48 17-48 37 E longitudes. The study area consisted of ten sites in the pasture, seven sites in the rainfed and three sites in the irrigated lands. The geographical positions of study sites were determined by a global positing system (GPS). Soil infiltration rates were measured by double rings method at three replications in each site. Variation of soil infiltration rate was determined for each land use. Soil samples were collected at three replications from each site to determine other physicochemical soil properties. Particle size distribution, bulk density, saturation percentage, aggregate mean weight diameter, organic matter, and equivalent calcium carbonate were determined using standard methods in the lab. Mean comparisons of infiltration rate along with other physicochemical soil properties among the land uses were done using the Duncan's parametric method. The Pearson’s correlation coefficients were used to determine the relationships between soil properties and soil infiltration rate.
Results and Discussion Based on the results, no significant difference was observed between the land uses in particle size distribution. Soil infiltration rate showed different patterns among the land uses, so that significant difference was observed among them (p< 0.01). Pastures showed the lowest infiltration rate among the land uses (about 86 and 66 times lower than that of the rainfed and the irrigated lands, respectively). This result was associated with increasing soil compaction through the over-grazing in the pastures. Positive correlation was found between soil infiltration rate and aggregate mean weight diameter(r= 0.54, p< 0.05) while its correlation with bulk density was negative (r= -0.74, p< 0.01). Pastures showed the lowest organic matter content (1.35%) as well as aggregate mean weight diameter (1.12 mm) as compared with other land uses. Since the pastures are located on the steeper slopes, they have the highest intrinsic potential to runoff production and soil erosion as compared to other land uses. As a consequence, the over-grazing is the major factor of soil structure breakdown, soil compaction, and in consequence declining soil infiltration rate in the pasture lands.
Conclusion: Pastures with poor vegetation cover appeared the lowest soil infiltration capacity as compared to other land uses in the catchment. Decreasing soil infiltration rate was associated with increasing bulk density in the area. It seems that overgrazing in the pastures increases soil bulk density and leads to decline the soil organic matter content as well as soil aggregation and aggregate stability. According to the results, pastures have the highest potential to runoff production and soil erosion rather than the other land uses (rainfed lands and irrigated lands). Therefore, maintaining vegetation cover and preventing over-grazing in the catchment is recommended to increase soil organic matter content and decrease soil compaction. These practices improve the hydraulic soil characteristics especially infiltration rate and in consequence decrease the catchment potential to runoff production and soil erosion.
Y. Ramezani; M. Ghomeshi; H. Khozeyme Nejad
Abstract
Bridge failures due to scour at bridge abutments clarify importance of scour prediction and scour countermeasures. Most of bridge abutments are located in floodplains. One of common cases in floodplains is the existence of vegetation cover. Scope of this study is investigation on effect of vegetated ...
Read More
Bridge failures due to scour at bridge abutments clarify importance of scour prediction and scour countermeasures. Most of bridge abutments are located in floodplains. One of common cases in floodplains is the existence of vegetation cover. Scope of this study is investigation on effect of vegetated floodplain on vertical wall abutment scour in compound channels. Results show, for constant abutment length and flow depth, with increasing the vegetation concentration, scour depth decreased with an increasing rate. For constant vegetation concentration and abutment length, with increasing the flow depth, effect of vegetation in reduction of scour depth decreased. In abutment with the lengh of 26 cm and concentration with s=8, with increasing the flow depth from 4.8 to 11.8 cm, percentage reduction in scour depth decreased from 40 to 22 percent. Also, vegetation reduces scour hole dimensions and has effect on downstream topography.
R. Erfanzadeh; J. Motamedi
Abstract
In this study, Khanghag Sorkh watershed was selected to study on the effect of vegetation and slope changes on soil carbon sequestration. Therefore, three vegetation communities were recognized and soil sampling was done within 0-30 cm depth in two slopes (10-30% and 30-50%). Soil samples were analyzed ...
Read More
In this study, Khanghag Sorkh watershed was selected to study on the effect of vegetation and slope changes on soil carbon sequestration. Therefore, three vegetation communities were recognized and soil sampling was done within 0-30 cm depth in two slopes (10-30% and 30-50%). Soil samples were analyzed to measure carbon sequestration rate and some of other physico-chemical characteristics. The results showed that the soil of Pteropyrum aucheri-Astragalus microcephulus, Astragalus microcephulus-Acanthophyllum microcephalum and Pteropyrum aucheri-Prangus uloptera communities has sequestrated 96.10, 73.84 and 52.85 ton carbon per hectare, respectively. The slope of 10-30% and 30-50% has sequestrated 96.11 and 126.68 ton carbon per hectare, respectively. In general, the slope of 10-30% had higher carbon sequestration compared with the slope of 30-50% with the exception of Pteropyrum aucheri-Astragalus microcephulus community. Our estimations revealed That the soil of Pteropyrum aucheri-Astragalus microcephulus, Astragalus microcephulus-Acanthophyllum microcephalum and Pteropyrum aucheri-Prangus uloptera had ca. 19220$ , 14768 and 10570$ economical values per hectare in respect to carbon fixation, , respectively. An investigation on other edaphic factors showed that most of soil factors were also significantly different between vegetation communities and slope classes (P
