Guna N. Paudyal

Bio: Guna N. Paudyal is an academic researcher from Asian Institute of Technology. The author has contributed to research in topics: Irrigation management & Nonlinear programming. The author has an hindex of 7, co-authored 10 publications receiving 242 citations.

Irrigation planning by multilevel optimization

Abstract: The complex problem of irrigation management in a large heterogeneous basin is solved by using a multilevel optimization technique. The real problem consists of determining the optimal cropping patterns in various subareas of the basin, the optimal design capacities of irrigation facilities including both the surface and ground water resources, and the optimal water allocation policies for the conjunctive use. The objective of such a management is to obtain a high level of economic efficiency in the irrigation development and water use system within a hydrologically feasible policy domain. Various alternative activities, such as surface water diversion and pumpage, ground water withdrawal and recharge, and alternative future operational scenarios, have to be analyzed in an integrated way. The solution strategy is based on the physical decomposition of a large system into interconnected subsystems. A computationally efficient algorithm that can be implemented in a microcomputer is developed to solve the mu...

Two-step dynamic programming approach for optimal irrigation water allocation

Abstract: A two-step (deterministic and stochastic) dynamic programming approach has been introduced in this study to solve the complex problem of optimal water allocation in a run-of-the-river-type irrigation project. The complexity of a real-world situation is represented by incorporating in the optimization model the stochasticity of water supply and the nonlinearity of crop production functions. A nonlinear, dated, and multiplicative production function is transformed into a sequentially additive type to replace the usual method of creating an additional ‘state of the plant variable’ which only increases the dimension of the problem. As compared to the explicit stochastic dynamic programming which necessitates, along with its use, an enormous computational complexity due to the so-called ‘curse of dimensionality’, the present model can approximate the theoretical global optimum, at least for the present case study, with a dramatic reduction in computer processing time. It also eliminates the rigidity of the policy derived by the explicit approach, since it provides irrigation planners with alternative decision policies which incorporate intangibles and other nonengineering factors. The traditional method of fixing the cropping pattern based on deterministic estimates of a dependable water supply can likewise be evaluated by the use of the present model. The results of the model's application appear to be practically acceptable.

Characteristics of free surface flow over gravel bed

Abstract: Measurements of velocity profiles of a free surface flow over a permeable gravel bed indicate that the logarithmic velocity distribution can be preserved if the reference datum is located a small distance equal to about one third of the median diameter of the bed particles below the surface. The observed value of 0.28 for the Karman constant is significantly reduced below the commonly expected value of 0.4 for impervious boundaries which indicates that the boundary resistance of the permeable bed is higher than that of the impermeable bed having identical rugosity. It is also observed that the friction factor increases with the increase in Reynolds number. A method is proposed to predict the amount of seepage flow through the permeable bed by measuring the hydraulic gradient and the velocity profile above the bed; and the bed material properties such as grain size and permeability. Although the measured bed flow showed considerable deviations from the predictions for the present experiments, the proposed method can be usefully applied in practical problems.

Flow Turbulence over Fixed and Weakly Mobile Gravel Beds

Abstract: Characteristics of turbulence structure in quasi-2D flows with static and weakly mobile gravel beds are presented. Three sets of measurements with acoustic Doppler velocimeters in an irrigation canal were used: two with subcritical bed shear stress (static beds) and one with the bed shear stress τo close to critical τoc (weakly mobile bed). The analyses included vertical distributions of local mean velocities, turbulence intensities, turbulent shear stresses, velocity auto- and cross-spectra, the quadrant method, and high-order velocity moments. A number of properties of turbulence intensities, high-order moments, streamwise bursting parameters, and velocity spectra appeared to be similar for all three flows, but some properties were different. The most important one was an observed reduction in the von Karman constant for the flow with weakly mobile bed. Comparison of these results with other studies and analogies with drag-reducing flows suggest that at τo/τoc ≈ 1 the drag on the bed for a given granula...

The Inter-Valley Soil Comparative Survey: the ecology of Dry Valley edaphic microbial communities.

Abstract: Recent applications of molecular genetics to edaphic microbial communities of the McMurdo Dry Valleys and elsewhere have rejected a long-held belief that Antarctic soils contain extremely limited microbial diversity. The Inter-Valley Soil Comparative Survey aims to elucidate the factors shaping these unique microbial communities and their biogeography by integrating molecular genetic approaches with biogeochemical analyses. Although the microbial communities of Dry Valley soils may be complex, there is little doubt that the ecosystem's food web is relatively simple, and evidence suggests that physicochemical conditions may have the dominant role in shaping microbial communities. To examine this hypothesis, bacterial communities from representative soil samples collected in four geographically disparate Dry Valleys were analyzed using molecular genetic tools, including pyrosequencing of 16S rRNA gene PCR amplicons. Results show that the four communities are structurally and phylogenetically distinct, and possess significantly different levels of diversity. Strikingly, only 2 of 214 phylotypes were found in all four valleys, challenging a widespread assumption that the microbiota of the Dry Valleys is composed of a few cosmopolitan species. Analysis of soil geochemical properties indicated that salt content, alongside altitude and Cu2+, was significantly correlated with differences in microbial communities. Our results indicate that the microbial ecology of Dry Valley soils is highly localized and that physicochemical factors potentially have major roles in shaping the microbiology of ice-free areas of Antarctica. These findings hint at links between Dry Valley glacial geomorphology and microbial ecology, and raise previously unrecognized issues related to environmental management of this unique ecosystem.

Colonization patterns of soil microbial communities in the Atacama Desert

Abstract: The Atacama Desert is one of the driest deserts in the world and its soil, with extremely low moisture, organic carbon content, and oxidizing conditions, is considered to be at the dry limit for life. Analyses of high throughput DNA sequence data revealed that bacterial communities from six geographic locations in the hyper-arid core and along a North-South moisture gradient were structurally and phylogenetically distinct (ANOVA test for observed operating taxonomic units at 97% similarity (OTU0.03), P <0.001) and that communities from locations in the hyper-arid zone displayed the lowest levels of diversity. We found bacterial taxa similar to those found in other arid soil communities with an abundance of Rubrobacterales, Actinomycetales, Acidimicrobiales, and a number of families from the Thermoleophilia. The extremely low abundance of Firmicutes indicated that most bacteria in the soil were in the form of vegetative cells. Integrating molecular data with climate and soil geochemistry, we found that air relative humidity (RH) and soil conductivity significantly correlated with microbial communities’ diversity metrics (least squares linear regression for observed OTU0.03 and air RH and soil conductivity, P <0.001; UniFrac PCoA Spearman’s correlation for air RH and soil conductivity, P <0.0001), indicating that water availability and salt content are key factors in shaping the Atacama soil microbiome. Mineralization studies showed communities actively metabolizing in all soil samples, with increased rates in soils from the southern locations. Our results suggest that microorganisms in the driest soils of the Atacama Desert are in a state of stasis for most of the time, but can potentially metabolize if presented with liquid water for a sufficient duration. Over geological time, rare rain events and physicochemical factors potentially played a major role in selecting micro-organisms that are most adapted to extreme desiccating conditions.