Multi-dimensional analysis of soil moisture dynamics in trickle irrigated fields. I: Mathematical modelling

An approach is presented to model soil moisture dynamics in irrigated fields. A generalised conceptual model is proposed for moisture transfer in response to hydraulic and thermal gradients. A model to stimulate moisture extraction by roots is presented, based on a philosophy related to fundamental physical principles and recent experimental evidence. The combined models are interpreted numerically by the finite element method and a number of numerical techniques are developed to treat time-dependent, nonlinear and moving boundary conditions. The approach is sufficiently general and is independent of the method of water application being considered. Its benefits are particularly magnified in studies of localised irrigation, where complex soil-water distribution patterns evolve.     

Development and testing of soil water regime simulation models

Four soil water balance simulation models corresponding to specific soil-crop relations were developed for application to irrigation planning and management. The forms of the models were inferred from 18 months of weekly and bi-weekly soil water data and daily meteorological data. Soil water change is computed by budgeting of the water inputs and outputs, namely precipitation, evapotranspiration, drainage, and runoff. Actual evapotranspiration was found to be dependent on both potential evapotranspiration and soil water content. Empirical drainage functions were developed, but semi-empirical ones inferred from theoretical knowledge of soil hydraulic properties performed at least as well. Runoff functions were required to explain only exceptional conditions of very heavy rainfall. A quantitative assessment of each model's prediction accuracy was performed. The uncertainty that can be expected for any predicted value with a cumulative probability of 0.95 is in all cases within an interval of 1% of the soil water content in average conditions.     

微集水种植技术对北方旱作农业区土壤水分影响

利用微集水种植技术,在我国北方旱作农业地区开展节水灌溉种植,研究不同微集水种植技术对该地区土壤水分的影响。研究结果表明：在不同降水年份,相对于传统种植模式,各微集水种植模式能够明显提高土壤蓄水保墒效果,在玉米生育期内,微集水处理在0-160cm土层的蓄水量要好于传统种植模式。     

土壤墒情自动化监控系统研究

土壤墒情自动化系统可为节水灌溉及排涝抗旱工作提供强有力的技术支持,将产生较大的社会与经济效益.对在作物生长过程中起关键作用的土壤湿度、降雨量、地下水水位等因子进行采集,并对作物的实时生长情况进行视频监控.在此基础上,通过构建计算机信息平台,对监测采集的数据进行存储计算.根据收集的土壤含水量数据信息,建立灌溉智能决策系统,通过开发基于B/S结构的系统网站访问模式,实现土壤墒情自动化监控.     

土层水量平衡模型在土壤墒情预报中的应用

针对宁夏项目区的实际状况,运用土层水量平衡模型来预报当地土壤墒情,发现该模型计算所得的土壤含水率与实测值比较符合,且应用时具有所需信息量少、实用性强和操作方便等特点。     

太行山山地丘陵区雨季土壤水分动态规律研究——以崇陵流域为研究区

以河北易县崇陵丘陵山区为研究对象,在实验的基础上,针对主要土壤质地、坡度和植被,研究不同下垫面条件下土壤水分变化规律,得到典型土壤质地的物理参数,并对土壤水分的动态变化规律进行了研究。实验结果表明,土壤质地对土壤物理参数和土壤水分变化影响非常大,明显强于植被和坡度。土壤质地对表层和深层水分的变化影响很大,活跃层受质地影响相对较小。     

半干旱区深层土壤水分含量特征

由于浅层地下水位大幅度下降,太行山山前平原半干旱区形成厚达20～30m的不饱和层。本研究就该区厚不饱和层土壤水分状况及其主控因素展开研究,以期为已有土壤水分运动模型及开发新模型提供参数依据。研究在河道区利用钻机进行深层土壤取样,利用相关分析和回归分析对近20m厚的不饱和层中土壤含水量及岩性的关系进行了分析。河道区岩性较单一,含水量变异较小,2m以下土壤含水量与岩性具极高的相关性,可以初步认为厚不饱和层土壤含水量处于田间持水量状态,并且通过回归方程根据岩性可以估算土壤含水量。     

吉林省中西部土壤墒情分析

根据吉林省的连续干旱形势及多年的监测结果,对吉林省中西部的旱情发生、发展规律,进行分析阐述。旱情主要发生在春季4—6月,变化趋势是由西向中西部蔓延。本文通过分析气象因子对土壤含水量的作用,认为用饱和差作主要参数,建立土壤墒情预测预报机制,进行土壤含水量的预测预报是可行的。     

真空负压对土体结构中水分运动影响试验探讨

本文通过模型试验,讨论了真空负压对土体结构中水分运动影响及快速排出水分的条件。针对本试验,把Darcy定律应用于非饱和带内水的运动,对非饱和渗流规律进行了初步讨论。     

温室熵灌线土源土壤水分运动数值模拟

根据土壤水动力学理论，考虑西江柿根系吸水，建立了西红柿生长条件下温室地表滴灌剖面二维土壤水分运动的数学模型，采用ADI法和Gauess-Seidel法联合求解数学模型，并进行了数值模拟，结果表明，温室土壤水分负压的监测值与计算值有着较好的一致性，这对温室地表滴灌灌溉制度的制定具有一定的指导意义。     

节水灌溉对玉米田间土壤水分的影响

通过设置充分灌溉、节水20％、节水40％3种灌溉方式对玉米田间土壤中水分含量及变化情况进行研究,结果表明,节水20％处理下土壤中的水分含量相对较高,利于玉米生长;且在各个处理的苗期,各层土壤中的水分变化不大,拔节期后,0―40cm土层变化剧烈,60―100cm则相对平缓,得出玉米的根系主要分布在0―40cm土层中。     

渠系基础冻结过程水热耦合问题数值分析

本文对冬季条件下渠道基础冻结过程的非线性、非稳定水热耦合问题进行了数值模拟，应用系数效应滞后的变物性全隐差分格式对水热耦合问题进行了数值计算     

辽宁省土壤墒情测报与抗旱决策支持系统初步设计

辽宁省是一个水旱灾害频繁的省份,开发和建设辽宁省土壤墒情测报与抗旱决策支持系统,对于促进我省经济和社会可持续发展具有重要意义。本文介绍了辽宁省土壤墒情监测系统的现状及决策支持系统的设计。     

Modelling and prediction of phyto- and zooplankton dynamics in Lake Kasumigaura by artificial neural networks

An artificial neural network model was developed for Lake Kasumigaura to predict timing and magnitudes for chlorophyll a, five species of blue-green algae and three zooplankton groups. The model was trained by 8 years of limnological time series and validated by two independent years. The validation showed the potential of neural networks as predictive tools for highly non-linear phenomena such as blue-green algal blooms in freshwater lakes.     

Technical Communication: Two-Phase Stochastic Dynamic Programming Model for Optimal Operation of Irrigation Reservoir

A two-phase stochastic dynamic programming model is developed for optimal operation of irrigation reservoirs under a multicrop environment. Under a multicrop environment, the crops compete for the available water whenever the water available is less than the irrigation demands. The performance of the reservoir depends on how the deficit is allocated among the competing crops. The proposed model integrates reservoir release decisions with water allocation decisions. The water requirements of crops vary from period to period and are determined from the soil moisture balance equation taking into consideration the contribution of soil moisture and rainfall for the water requirements of the crops. The model is demonstrated over an existing reservoir and the performance of the reservoir under the operating policy derived using the model is evaluated through simulation.     

Simulation of water allocation and salt movement in the root zone

This paper is concerned with the simulation of the water allocation and salt movement in the root zone of a particular crop. A mathematical model of four ordinary differential equations is developed. The model performs water balance and salt balance in unsaturated and saturated regions of the root zone. It is a lumped input and lumped parameter conceptual model, which considers the average soil moisture and salt concentration in the root zone. The equations are solved numerically over the time period of the growing season. Precipitation and irrigation water are treated as inputs.The analyzed results indicate that, for the shallow water table case, the water table elevation has an important effect on the soil moisture depletion dynamics of the unsaturated zone. An appreciable amount of water from the saturated zone is transferred through capillary rise to the unsaturated zone particularly in the case of sandy loam soils. It was found that the water table elevation varies significantly during the growing season.The salt movement simulation indicates a salt concentration build up in the unsaturated zone during the growing season. Contours of equal crop yield reduction as a function of the unsaturated zone initial salt concentration and the irrigation water salt concentration are obtained.The model was tested with data from the Mashtul Pilot Area in Egypt and its performance was satisfactory.     

Appraisal and optimization of agricultural water use in large irrigation schemes: II. Applications

In this paper, the theoretical approach presented in Part I is demonstrated by means of case studies on the irrigation schemes of Rio Mendoza and Rio Tunuyán in the Province of Mendoza, Argentina. The object of the case studies was the determination of optimal allocation of surface water to reduce the use of groundwater. Current and optimal conjunctive allocation of ground and surface water is studied by means of the developed simulation and optimization models.The second case study was designed on the basis of the experience gathered during the first one: each step of the case studies is compared. The comparison between the two case studies illustrates how to apply the proposed approach when the amount and quality of available data are different. For the more detailed Rio Tunuyán study, we determined the following physical characteristics of all terminal nodes: on-farm rotational intervals, mean water application depth, actual soil water storage capacity, crop water requirements, depth of groundwater table, aquifer transmissivity, and efficiency of groundwater use.The performance of the entire system is sensitive to changes in the water application depth, as it was shown by a simulation study.The application of our optimization approach to the conjunctive use of ground- and surface water showed that the total water requirements over a year can be met by a reassignment of water that reduces the total costs of a great amount.     

Soil-moisture deficit simulations with models of varying complexity for forest and grassland sites in Sweden and the U.K.

Using soil moisture observations from a forest area in the U.K. and from forest and grassland sites in southern Sweden, a range of simple, daily soil moisture deficit models were tested. Each model consists of potential evaporation, interception losses, and a routine by which transpiration was calculated from the potential via a soil water regulating function. In the case of the Swedish sites, snow melt and temperature effects on transpiration rates were also included.Despite the large range of vegetation and soil types, the same conbinations of models generally gave the best fit to the observations. Also, in most cases, the most successful model used the simple subroutines.At each site, it was found essential to optimize the transpiration regulating function. The most successful model was a linear formulation using the concept of available soil water. A good relationship was found between the model-derived available water and field-capacity values, and the measurements of soil-water potentials. This suggests that these models could be calibrated using simple measurements on the soils.Finally, the analysis illustrates some important physical processes, notably the negative feedback between transpiration and high evaporative demand, the limitation of transpiration by low temperatures, and the possibility of drainage of rainwater through unsaturated soils.     

Irrigation management transfer in sub-Saharan Africa: an analysis of policy implementation across scales

ABSTRACT

This article explores how irrigation management transfer policies were implemented in Mali, Mozambique, Malawi and Zimbabwe. In Mali and Mozambique, where the irrigation bureaucracy controlled one large irrigation system, state agencies retained control over irrigation management despite reduced state funding. In Malawi and Zimbabwe, where the state irrigation systems and the irrigation bureaucracy were smaller, users have taken over irrigation management, but are having trouble sustaining irrigated agriculture. We show how irrigation management transfer policies were shaped by the interplay between international donors, macro-economic dynamics, national politics and the interactions with (and the nature of) irrigation infrastructure, bureaucracies and organized users.     

Eutrophication risk assessment in Hamilton Harbour: System analysis and evaluation of nutrient loading scenarios

Environmental modeling has been an indispensable tool of the Hamilton Harbour restoration efforts, where a variety of data-oriented and process-based models have been used for linking management actions with potential ecosystem responses. In this study, our objective is to develop a biogeochemical model that can effectively describe the interplay among the different ecological mechanisms modulating the eutrophication problems in Hamilton Harbour, Ontario, Canada. First, we provide the rationale for the model structure adopted, the simplifications included, and the formulations used during the development phase of the model. We then present the results of a calibration exercise and examine the ability of the model to sufficiently reproduce the average observed patterns along with the major cause–effect relationships underlying the Harbour water quality conditions. The present modeling study also undertakes an estimation of the critical nutrient loads in the Harbour based on acceptable probabilities of compliance with different water quality criteria (e.g., chlorophyll a, total phosphorus). Our model suggests that the water quality goals for TP (17 μg L⁻¹) and chlorophyll a concentrations (5–10 μg L⁻¹) will likely be met, if the Hamilton Harbour RAP phosphorus loading target at the level of 142 kg day⁻¹ is achieved. We also provide evidence that the anticipated structural shifts of the zooplankton community will determine the restoration rate as well as the stability of the new trophic state in the Harbour.