Narendra Kumar Tuteja

Partitioning the effects of pine plantations and climate variability on runoff from a large catchment in southeastern Australia

[1]xa0Effects of substantial increase in area of pine plantations from 1960 to 2000 on runoff in a large catchment in southeastern Australia are quantified. Reliable land use maps were prepared for 1960–1979, 1980–1989, and 1990–2000 conditions from various data sources. Land use changes in the subcatchments have occurred at varying rates (16 to 28%) with pines replacing pasture and native woody vegetation. On the basis of long-term trends in rainfall-runoff relationships, flow duration curves, and history of land use changes, it is shown that there is strong evidence of reduction in runoff over a wide range. Modeling methodology using a lumped catchment-scale rainfall-runoff model (SMAR) and landscape-scale ecohydrological models (CLASS U3M-1D, CLASS PGM, and 3PG+) was implemented in a catchment framework to partition the effects of land use change and climate variability during 1960–2000. Runoff reductions from land use change in the range 22–52 mm/yr are estimated for different subcatchments. Annual yield impact per 10% of the catchment forested (AYI/10%) from catchment-scale modeling is estimated to vary between 14.3 to 19.2 mm/yr for the subcatchments. AYI/10% from landscape-scale modeling is estimated to vary between 12.8 to 21.3 mm/yr.

Predicting the effects of landuse change on water and salt balance—a case study of a catchment affected by dryland salinity in NSW, Australia

An integrated and comprehensive framework for the assessment of water and salt balance for large catchments is presented. The framework is applied to the Mandagery Creek catchment (1688 km2), located in the south-eastern part of Australia. The catchment is affected by dryland salinity and the effects of landuse, climate, topography, soils and geology on water and salt balance are examined. Landuse change scenarios designed to: (a) increase the perennial content of the pastures and crop rotations and (b) increase the current remnant native woody vegetation with additional tree cover are investigated to determine the level of intervention required to develop ameliorative strategies. Likely downstream impacts of the reduction in water flow and salt export are also estimated.

A GIS‐Based Tool for Spatial and Distributed Hydrological Modelling: CLASS Spatial Analyst

CLASS Spatial Analyst is a GIS tool which can be used to support spatially distributed hydrological modelling. The tool generates a number of spatial layers that can be used for many practical applications. These include climate zoning, multi-resolution DEMs, Compound Topographic Index (CTI) (also referred to as Topographic Wetness Index, TWI), lateral multiple flow paths, accumulation and dispersion of water and solutes from hazard areas, estimation of soil depth, soil material/horizon distribution and soil moisture storage capacity in different parts of the landscape. Although each of these tasks can be undertaken separately using spatial software packages such as ArcGIS, GRASS, TIME, and MapInfo, this tool puts together all these tasks into a single application which provides the user with an option of undertaking some or all of them within this application. The technology used in this tool is supported by various peer-reviewed publications (e.g. Tarboton 1997, Gallant and Dowling 2003).

Development and implementation of a generic pasture growth model (CLASS PGM)

This paper describes the development, testing and implementation of a generic pasture growth model (CLASS PGM) which can be used to simulate growth of composite pasture types of multiple species that may be summer or winter active, perennial or annual. The model includes carbon assimilation through photosynthesis and respiration followed by tissue growth, turnover and senescence. Environmental conditions as well as soil water, nutrient and salinity status influences pasture growth and tissue dynamics. The model allows the user to simulate a range of grazing management strategies. Concepts and theoretical basis of the pasture growth model is based upon the detailed technical report on pasture and crop growth modules (Johnson, 2003). For water balance computations, PGM is internally linked to the Richards equation - based hydrology tool, Unsaturated Moisture Movement Model U3M-1D (Vaze et al., 2004b) PGM is supported by a windows based user friendly graphical users interface (GUI). The model can be downloaded free from the Catchment Modelling Toolkit website supported by the eWater Cooperative Research Centre (http://www.toolkit.net.au/class). This paper gives an overview of the model structure, model inputs and outputs and the soils related inbuilt database. Results from model validation using long term observed data for soil moisture, pasture herbage mass and grazing for a grazing experiment at Wagga Wagga, New South Wales, Australia are discussed. When compared with herbage mass and soil moisture data from the experiment, PGM was found to adequately simulate the patterns and amplitudes of pasture growth and soil moisture recorded in the experiment.

Delineating hydrologic response units in large upland catchments and its evaluation using soil moisture simulations

We present here a basis for delineating Hydrologic Response Units (HRUs) to capture heterogeneity in the catchments topography, landforms and geomorphologic attributes. To delineate topologically connected HRUs, the catchment is divided into four landforms and sub-basins. These four major landforms represent macroscopic changes in the catchment landscapes, using thresholds derived from a range of terrain analysis techniques - the Cumulative Area Distribution (CAD) curve, average local slope, curvature, Compound Topographic Index (CTI) and the MultiResolution Valley Bottom Flatness (MRVBF) index. The adequacy of the HRUs delineation approach is ascertained by soil moisture movement modelling in the unsaturated zone based on a two-dimensional solution of Richards equation, across multiple cross-sections of the catchment. The modelling results of the four landform delineated cross-sections are compared with those from the simplest case of a single landform delineated cross-section and with the most complex case of cross-sections divided on a pixel basis. The modelling results indicate gain in accuracy when using the four landform formulation compared to the use of a single landform, and little loss of accuracy compared to simulations on a pixel basis. This study investigates the stability of this HRUs delineation methodology using the data for the Maclaughlin, Bombala and Delegate catchments of the Snowy River at Burnt Hut, New South Wales, Australia.

Development of a computationally efficient semi-distributed hydrologic modeling application for soil moisture, lateral flow and runoff simulation

A new automated workflow based computationally efficient hydrologic modeling application is developed for soil moisture and runoff simulation. The spatially distributed conceptual framework underpinning the Soil Moisture And Runoff simulation Toolkit (SMART) resolves water balance in large upland catchments where topography and land cover are significant drivers of rainfall-runoff transformations. SMARTs computational efficiency is achieved by delineation of contiguous and topologically connected hydrologic response units and solving the water balance equation on spatially representative Equivalent Cross-Sections (ECSs). ECSs are formulated by aggregating topographic and physiographic properties of the complete or part of the first order Strahler sub-basins, thereby reducing the number of computational elements. Water balance simulations across the ECSs in two sub-basins illustrated little loss of accuracy compared to the distributed cross section delineations and soil moisture observations. A 2-dimensional Richards equation based hydrologic model in SMART can be augmented with additional functionalities or replaced with other model structures. SMART is a new semi-distributed hydrologic modeling application applied to topologically connected HRUs.SMART workflow automates sub-basin, HRU and cross section or equivalent cross section delineations of the entire catchment.SMART reduces computational time of large catchment scale simulations by reducing the number of computational elements.Temporal dynamics of sub-basin soil moisture are reasonably captured using parameters obtained from soil and land cover data.

An equivalent cross‐sectional basis for semidistributed hydrological modeling

The computational effort associated with physically based distributed hydrological models is one of their major limitations that restrict their application in soil moisture and land surface flux simulation problems for large catchments. In this work, a new approach for reducing the computational effort associated with such models is investigated. This approach involves the formation of equivalent cross sections, designed in a manner that ensures comparable accuracy in simulating the hydrological fluxes as a fully distributed simulation. Single or multiple equivalent cross sections are formulated in each Strahlers first-order subbasin on the basis of topographic and physiographic variables representing the entire or part of the subbasin. An unsaturated soil moisture movement model based on a two-dimensional solution of the Richards equation is used for simulating the soil moisture and hydrologic fluxes. The equivalent cross-section approach and the model are validated against observed soil moisture data in a semiarid catchment and found consistent. The results indicate that the equivalent cross-section approach is an efficient alternative for reducing the computational time of distributed hydrological modeling while maintaining reasonable accuracy in simulating hydrologic fluxes, in particular dominant fluxes such as transpiration and soil evaporation in semiarid catchments.

Soils fieldwork, analysis, and interpretation to support hydraulic and hydrodynamic modelling in the Murray floodplains

There are limited datasets which cover the heavy clays found in the Murray floodplain area. To understand the processes associated with the water balance within the Koondrook–Perricoota Forest (KPF), detailed hydraulic and hydrodynamic modelling of the flood inundation patterns and overland flow in the KPF is required. Reliable and accurate soils information is critical for any credible hydrologic or hydrodynamic modelling results. Extensive fieldwork across the entire KPF and detailed laboratory testing of the collected samples was undertaken to produce soils information including: spatial distribution of soil types, soil stratigraphy along the surface and subsurface flowpaths, soil hydraulic properties, soil salinity, and soil organic matter. Soil sampling and soil profile descriptions were undertaken at 26 sites spread across the forest. Deep drilling was done at 12 sites to check the existence of ancestral streams and for salinity profiles; soil hydrology testing to estimate infiltration rates was undertaken at 10 sites. Rapid appraisal methods for soil infiltration were developed for the project. Results were compared to soil pedotransfer functions generated from laboratory results; soil indexes including the dispersibilty index and electrochemical stability index; and typical infiltration and permeability rates inferred from soil texture and structure. The results from this study and the archived soil physical and hydraulic datasets can be used for any detailed hydraulic or hydrodynamic modelling exercise in the Murray floodplain area with similar soil properties.

Overview of Communication Strategies for Uncertainty in Hydrological Forecasting in Australia

In contrast to deterministic forecasts, ensemble forecasts are a multiple forecasts of the same events. The ensemble forecasts are generated by perturbing uncertain factors such as model forcings, initial conditions, and/or model physics.

Applicability of Hydrologic Response Units in low topographic relief catchments and evaluation using high resolution aerial photograph analysis

Topography and geomorphology of a catchment are major drivers of runoff generation. In an earlier publication by the authors, a novel approach of delineating Hydrologic Response Units (HRUs) was investigated with reference to high topographic relief catchments. In the present study, this approach is evaluated for low topographic relief catchment and found to be applicable. To verify the proposed HRUs delineation logic, the thresholds derived from the DEM analysis are evaluated here at catchment scale using high resolution aerial photograph analysis and associated site visits. The thresholds derived from the DEM analysis are found in the same range as obtained from the aerial photographs analysis. The adequacy of the HRUs delineation approach is further verified by soil moisture movement modelling across four cross-sections and sensitivity analysis test for one cross-section in the Little River catchment which further supports the application of HRUs delineation approach in low topographic relief catchment. Evaluation of HRUs using high resolution aerial photographs.Extension of HRUs in low topographic relief catchment.Analysis of upslope areas of channel head in the different rock types.Verification of HRUs using soil moisture movement modelling.