Journal of Water Resources Engineering
Year:2011 | Volume:4 | Issue:9|Papers Count:8

The Neyshabur Plain has encountered increasing recession in watertable (WT) elevation in recent years. Therefore, prudent water resources management dictates implementation of a detailed study on groundwater accessibility in different locations of the plain. As rainfall distribution and geological settings of the various parts of the plain differ significantly, we tried to study the relationships of drought severity and duration (DSD) on the WT fluctuation in the plain. To correlate DSD with the WT elevation, we employed the Ward clustering technique to select representative piezometers at the following locations in the plain: 1. Sultan Abad Cluster, 2. Filkhaneh Cluster, 3. Amman Abad Cluster, 4. Arazie Mohandes Cluster, 5. Amir Abad Cluster, and 6. Hussein Abad Jangal Cluster. The mean annual precipitation of each cluster was calculated for the 1993-2006 duration using the inverse distance weight. Results of the Man-Kendall test showed that the slope of WT in the selected six piezometers had negative trends for different months. Therefore, the WT level was de-trended using the trend extrapolation method. Results of the correlation between the rainfall amount and "no trend" WT level indicated that the effects of rainfall on WT levels were repeated annually. Therefore, the standardized precipitation index (SPI) was devised to find the drought and wet period effects on the WT elevation. The analytical results showed that for clusters 1 through 6, the highest R2 between no trend WT elevation and the SPI with the time scales of 54, 42, 36, 48, 36 and 36 months equaled 0.405, 0.434, 0.063, 0.248, 0.362 and 0.211, respectively. Moreover, it was revealed the Aman Abad Cluster was affected by the groundwater movement and natural recharge taking place in the eastern part of the plain and Binaloud Ranges.

Drought is the most serious natural hazard that affects human societies in the arid- and semi-arid lands; therefore, contemplating its occurrence and severity is of the utmost importance in planning and implementing the water shortage crisis management. The main objective of this research was to develop an approach to analyze the spatial patterns of meteorological droughts based on annual precipitation data in the Province of Tehran. The normalized and standardized precipitation data were classified into certain degrees of drought severity (extreme, severe, mild, and non drought) based on a number of truncation levels corresponding to specified quartiles of the standard normal distribution using a nonparametric spatial analysis neural network algorithm. The probability of drought severity at any given point in the region was determined, and a point degree was assigned to it as a Bayesian drought severity index. This index was used for constructing the drought severity maps in the Province of Tehran that display the spatial variability of drought severity on an annual basis. The results indicated that in the 1974-2008 period, 16.7% of the years experienced extreme droughts, 26.65% suffered from severe droughts, 30.00% faced mild droughts, and 23.00% escaped droughts altogether.

Interpolation as an important technique has been widely used for evaluation of meteorological spatial variation. These techniques have been classified in different manner. In this study we applied kriging and cokriging techniques to the data collected at 12 meteorological stations to map spatial varations of mean annual precipitation in the Fars province. Experimental variogram for spherical, exponential and Gaussian models of ordinary kriging and cokriging were fitted and compared by cross validation techniques. Gaussian model with 200 kilometer range was selected with minimum MAE index as the best fitted one for the mean annual precipitation interpolation in this region.

Employing regional flood frequency analysis, a regionalized relationship may be established to estimate flood magnitudes for ungauged and poorly-gauged catchments. Regional flood frequency analysis is usually based on identification of homogeneous regions, selection of suitable regional frequency distribution, and estimation of flood quantiles at watersheds of interest. In this paper, L-moments techniques was used for regional floods frequency analysis in watersheds located in the Province of Gilan. In the conventional technique of regionalization, homogeneous hydrological regions are identified on the basis of watershed characteristics such as physiography, geographical location and flood flow data at the related hydrometric stations. In the present study, using the K-means clustering algorithm, the study area was divided into two sub-regions containing a total of 58 hydrometric stations. Indices of the Average Silhouette Width, Davies-Bouldin and Dunn were used to determine the optimal number of clusters and measurement of the global goodness of clustering. Homogeneity of the region was investigated by the discordancy measure and heterogeneity measure tests. Selection of the best categorization method of the regional distribution was assessed using the goodness of fit measure, and the generalized logistic for the regions 1 and 2 as the best categorization method to identify the regional distribution. Finally, the regional parameters of selected distributions and probability quantiles with different return periods were calculated.

Climate change is one of the most important challenges of mankind in the 21st century. Numerous climatic models have been developed to simulate and project the probabilities in changing climatic variables. Because of the uncertainty involved in using different models, simulations results were validated and the best of them for each variable was determined. In this study, simulation results of temperature parameters from 22 General Circulation Models, which have been approved by the Intergovernmental Panel on Climatic Change (IPCC), were evaluated for validity using the statistical criteria. It was observed that BCM2.0, CM3.0, INM, and AOM were appropriate for the minimum temperature prediction; HadGEM, ECHO, and G-Mk3.0 were useful for the mean temperature prediction; and PCM, Mk3.0, and AOM were appropriate for the maximum temperature prediction.

Irrigation requirement equals the difference between the water requirement and the effective rainfall. Crop water requirement and irrigation requirement have been reported by employing the NETWAT program for various crops for the different regions of Iran. However, as the means of climatological paremeters have been used in this program, therefore, the reported values of crop water- and irrigation requirement have been calculated for the 50 percent of probability level. As it is necessary in some conditions to determine irrigation requirement at the different probability levels, therefore, irrigation requirement of the most important agricultural crops were calculated for some regions of the Province of Fars namely: Abadeh, Eqlid, Darab, Dorodzan, Zarghan, Shiraz, Fasa and Lar, using the climatological data for at least 10 consecutive years. Irrigation requirement of each crop then was determined at the probability levels of 10, 20, 30, 40, 50, 60, 70, 80 and 90 percent. The results indicated that the obtained values for irrigation requirement for most conditions were different from those reported using the NETWAT program. Therefore, it is advisable to determine the irrigation requirement of the most important agricultural crops at the different probability levels using the results obtained in this study for the reported locations in the Province of Fars.

Surge irrigation, an intermittent release of water into furrows is an efficient method of water conservation if the flow and frequency of water delivery are optimized. It increases the advance velocity, causes uniform distribution over the furrows, and reduces deep percolation losses. The objectives of this study were to compare yield indices for surge flow and continuous flow, and to evaluate cycle ratios and suitable input discharge in the study area, and also to determine the difference of advance velocity of the wetting front between surge irrigations and continuous flow irrigations. Seventy meter long furrows, 0.5 and 2 lit/s discharge rates, and various pulse ratios were compared with the constant inflow. Field experiments were conducted including determination of the number of furrows and the number of surges, and continuous flow treatments (2 discharges and various cycle ratios for surge flow). Advance velocity, in-and-out flows, and soil water content prior and after the termination of irrigation were measured at the Khalatpoushan Research Station of the Tabriz University. Then flow parameters and infiltration rate for furrows were simulated using the SIRMOD surface irrigation model for both the surge and constant flows. In order to compare the advance velocity of wetting front for surge and continuous irrigations, the HYDRUS 2-D model was used for simulating the advance of wetting front in the wet soil volume in the furrow. The results of simulation show that the final infiltration rate during surge flow was half of continuous flow for one of the treatments. Advance velocity of wetting front in surge treatments was more than continuous treatments with the same volume of applied water. Overall, the S22 treatment (the inflow of 0.5 lit/s and the pulse ratio of 1:4) had the best performance, and S13 treatment (the inflow of 0.5 lit/s and the pulse ratio 2:3), had the poorest performance, even worse than constant flow treatments.

As water is the most precious commodity in dry lands, economizing its use is a matter of the utmost importance. Furthermore, drip irrigation has been proven to be a very efficient method of watering agricultural crops. Therefore, determination of the proper spacing of emitters with certain discharge capacity at specified pressure operated for a limited duration is a water saving strategy. To formulize the dimensions of the wetted bulb formed under each emitter, we studied the emitter discharge and duration of irrigation for a given volume water application. This experiment was carried out on a sandy loam soil at the Ghaeem-Abad Plain, in the Province of Kerman. The treatments were 3 discharge rates: 4, 8, and 24 liters per second per ha, and the different irrigation times (6 times related to emitter discharge). Twenty four hours after irrigation termination, when a relative steady state had been reached in the soil, we removed the laterals and emitters, dug trenches parallel to the laterals, and measured the dimensions of the wetted bulbs for different application rates and durations. We observed that for a given volume of water, the wetted radius on the soil surface was directly related to the rate of emitter discharge, while the depth to the wetting front was indirectly related to it. Prolongation of application for different emitter discharge rates increased both the radius and the depth to the wetting front. The wetting patterns were almost identical for the three discharge rates. The dimensions of the wetted bulb under emitters were directly related to the discharge rate. We have developed empirical equations, which predict the emitter spacing, the wetted radius on the soil surface, and application duration to supply the required water to a specified rooting zone.