A very large fraction of the water falling as rain on the land surfaces of the earth or applied irrigation water moves through unsaturated soil during the subsequent processes of infiltration, drainage, evaporation, and the absorption of soil-water by plant roots. The water movements in the unsaturated zone, together with the water holding capacity of this zone, are very important for the water demand of the vegetation, as well as for the recharge of the ground water storage. A fair description of the flow in the unsaturated zone is also crucial for predictions of the movement of pollutants into ground water aquifers.
A number of simulation models are available for investigating the soil water balance. SWIM (Soil Water Infiltration and Movement) is a physically based, isothermal, one dimensional model of water flow through the soil coupled with a simple crop water extraction model in which the growth of the canopy and of the root system is a predetermined input. SWIM is driven by rainfall and potential evaporation, and so appears to be more appropriate than few other similar models if the available meteorological data are limited.
The present study aims at modelling of soil moisture movement in Barchi watershed (Karnataka) using SWIM. Field and laboratory investigations were carried out to determine the saturated hydraulic conductivity at eight locations using Guelph Permeameter and soil moisture retention characteristics using the Pressure Plate Apparatus. The van Genuchten parameters of soil moisture retention function and hydraulic conductivity function were obtained through non-linear regression analysis. Daily rainfall and evaporation data of Barchi for the period 1996-97 to 1999-2000 were used for the simulations. Water balance components like runoff, evapotranspiration and drainage (groundwater recharge from rainfall) were determined through SWIM.
Table of Contents
1.0 INTRODUCTION
2.0 STUDY AREA
3.0 METHODOLOGY
3.1 General
3.2 Soil Moisture Characteristics
3.3 Soil Moisture Retention Curves
3.3.1 Pressure Plate Apparatus
3.4 Saturated Hydraulic Conductivity
3.4.1 Guelph Permeameter
3.5 van Genuchten Parameters
4.0 DESCRIPTION OF SWIM MODEL
4.1 Introduction
4.2 Water Movement
4.2.1 Richards’ Equation
4.2.2 Hydraulic Properties
4.2.3 Initial and Boundary Conditions
4.3 Solute Transport
4.3.1 Advection-Dispersion Equation
4.3.2 Solute Initial and Boundary Conditions
4.4 Limitations of the Model
5.0 ANALYSIS AND RESULTS
5.1 General
5.2 Soil Moisture Characteristics
5.3 Model Conceptualization
5.4 Simulation of Water Balance Components
5.5 Concluding Remarks
6.0 CONCLUSION
Research Objectives and Themes
The primary objective of this study is to simulate soil moisture movement in the Barchi watershed, Karnataka, using the numerical SWIM model to determine groundwater recharge and other water balance components.
- Measurement of saturated hydraulic conductivity and soil moisture retention characteristics.
- Application of the SWIM (Soil Water Infiltration and Movement) model for watershed analysis.
- Determination of water balance components, including runoff, evapotranspiration, and groundwater recharge.
- Fitting of soil data to the van Genuchten model to parameterize hydraulic functions.
Excerpt from the Book
3.2 Soil Moisture Characteristics
Quantitative measurements of soil physical properties are required for many purposes. In the area of land management, one may wish to know whether a particular management scheme will increase or decrease infiltration, runoff, erosion, leaching, salinization etc. We may need to predict material transport, such as the depth to a wetting front, position of a seepage face, time of arrival of a tracer plume, cumulative evaporation etc.
Any measurement of soil water in the field depends upon sampling at a given location, both in area and depth of soil profile, at a given time or times. These samples are then used to estimate the water condition of the entire area. Many methods are sufficiently accurate to measure the water condition in a given sample at a given time. Difficulty comes when one tries to apply these conditions to a large area or at a different time. In reality, the water condition measured is a transient one in a system that is continuously changing in three-dimensional space and time and the situation would likely be different at any other location at the same time, or at the same location at a different time.
Summary of Chapters
1.0 INTRODUCTION: This chapter introduces the importance of studying unsaturated soil water flow, describes the structure of subsurface formations, and identifies key processes like infiltration, percolation, and capillary rise.
2.0 STUDY AREA: This chapter provides a geographical description of the Barchi watershed, including its location, topography, land use, and general climate characteristics.
3.0 METHODOLOGY: This chapter details the field and laboratory investigations, focusing on measuring hydraulic properties and soil moisture retention curves using the Guelph Permeameter and Pressure Plate Apparatus.
4.0 DESCRIPTION OF SWIM MODEL: This chapter explains the theoretical basis of the SWIM model, specifically its numerical approach to solving the Richards’ equation for water movement and the advection-dispersion equation for solute transport.
5.0 ANALYSIS AND RESULTS: This chapter presents the data analysis, including the derivation of van Genuchten parameters, model conceptualization, and the simulation results of water balance components for the Barchi watershed.
6.0 CONCLUSION: This chapter summarizes the findings of the research and evaluates the effectiveness of using the SWIM model for predicting water balance in an unsaturated zone.
Keywords
Soil Moisture, SWIM Model, Barchi Watershed, Groundwater Recharge, Unsaturated Zone, Hydraulic Conductivity, van Genuchten Parameters, Infiltration, Evapotranspiration, Runoff, Water Balance, Guelph Permeameter, Pressure Plate Apparatus, Richards’ Equation, Solute Transport
Frequently Asked Questions
What is the primary focus of this study?
The study focuses on simulating soil moisture movement and determining groundwater recharge in the Barchi watershed using the SWIM (Soil Water Infiltration and Movement) model.
Which central topics are addressed?
The research covers soil physical properties, unsaturated zone hydrology, numerical modeling of water flow, and the impact of vegetation and climate on soil water balance.
What is the primary goal of the research?
The goal is to accurately model water movement through the unsaturated zone and calculate water balance components such as runoff, evapotranspiration, and recharge to the groundwater reservoir.
What methodology is employed?
The methodology includes field investigations using the Guelph Permeameter, laboratory analysis with the Pressure Plate Apparatus, and mathematical simulation using the SWIM model with van Genuchten parameters.
What does the main part of the report cover?
The main part covers the theoretical background of the SWIM model (Richards' equation), field data collection, the fitting of hydraulic parameters, and the final analysis of water balance simulations.
Which keywords best characterize the work?
Key terms include Soil Moisture, SWIM Model, Barchi Watershed, Groundwater Recharge, and Hydraulic Conductivity.
How is the van Genuchten model utilized in this study?
The van Genuchten model is used to fit the soil moisture retention and hydraulic conductivity data, providing necessary parameters for the numerical SWIM simulations.
What are the identified limitations of the SWIM model?
The model is limited to one-dimensional flow, assumes a rigid soil matrix, ignores soil airflow, and takes macropore or bypass flow into account only in a limited manner.
How are rainfall and evaporation data processed for the simulation?
Daily rainfall and evaporation data for the Barchi watershed from 1996 to 2000 were used to drive the simulation, with specific adjustments for rainfall distribution.
What were the results regarding runoff prediction?
The study found that the model initially underestimated runoff, leading to refinements in data distribution to improve agreement between observed and simulated values.
- Quote paper
- C. P. Kumar (Author), B. K. Purandara (Author), P. R. Rao (Author), 2014, Simulation of Soil Moisture Movement in a Hard Rock Watershed using SWIM Model, Munich, GRIN Verlag, https://www.grin.com/document/281973
