Rodger Grayson

Hydrology, it is a'changing. Throughout the 20th century, the rainfallrunoff relationship was a dominant paradigm for catchment hydrologists. It permeated applied hydrology in many guises, and also played a central role in many research endeavours. Despite the gradual ...

Estuarine systems such as the Gippsland Lakes (south eastern Australia) have an inherent value, environmentally and to the community through commercial fishing, tourism, recreation and their aesthetic appeal. Phosphorus (P) contributes to eutrophication and the development of algal blooms both in the Lakes and inflowing tributaries which negatively impact on these assets. Irrigated dairy production represents an important P source in some catchments. Of the 230 tonnes of P entering the Gippsland Lakes via Lake Wellington annually, approximately 53 tonnes or 23 % is from the Macalister Irrigation District (Grayson and Argent 2002). At a district or catchment scale, drainage networks are a significant pathway for the transport of P and at the catchment scale the drainage networks appear to act as a net sink for P. This paper investigates the effect of farm drains on P transport. Field scale investigations were used to explore the ability of farm scale drains to act as either sources o...

Spatial patterns of hydrological processes are a rich source of variability which in some instances is quite obvious to the observer, as in the case of spatial patterns of a seasonal snow cover; and in other instances is hidden from the eye and very difficult to identify by even the most sophisticated measurement techniques, as is the case with patterns of subsurface preferential flow paths. Part of the richness comes from the diversity in the spatial arrangement of hydrologically relevant variables. It is important to understand this arrangement to design measurement strategies adequately, to interpret the data correctly, to build and/or apply a model of catchment dynamics, and ultimately to use these data in predictions of the hydrological behaviour of catchments. There is a wide spectrum of ‘‘measurement techniques’’ (in a general sense) available for exploring these complex patterns, ranging from traditional stream gauging to remote sensing. Ideally, a measurement technique shou...

... Collingsworth Joan Countryman David D'Agostino Steven Deutsch Alec Dubro Bonnie Engdahl Theodore Franklin Ruben J. Garcia M. Kay Gartrell Stacie Harting Mark Heald Richard and Lucy Henighan Michael Hirschhorn Sidney Kalban Dan Kluger Ernest A. Landy Adam ...

It also seems obvious that search for new measurement methods that would yield areal distributions, or at least reliable areal totals or averages, of hydrologic variables such as precipitation, evapotranspiration, and soil moisture would be a much better investment for hydrology than the continuous pursuit of a perfect massage that would squeeze the nonexistent information out of the few poor anaemic point measurements . . .Klemeš (1986a, p. 187S)

It has long been recognized that soil moisture has a key role in controlling evapo- transpiration during dryer periods, as well as runoff processes, particularly saturation excess runoff. The temporal and spatial variability of moisture can be an important influence on the temporal and spatial characteristics of these processes. More recently, the role of soil moisture in controlling lateral flow processes has re- ceived close attention, with switching between persistent dry and wet states leading to switches between controls on spatial patterns of soil moisture and consequent changes in runoff behaviour. In this paper we will review results on the spatial and temporal variability of soil moisture at the small catchment scale, concentrating in particular on dominant controls and temporal changes in dominant controls. We will discuss the climatic and catchment characteristics under which switching between dominant controls is likely. We will also present results relating spatial soil moisture behaviour to soil moisture state and relating rainfall-runoff response to moisture state: in particular we investi- gated the relationships between the basin soil moisture dynamic and the occurrence of very extreme flood events. The spatial probability density function of soil moisture is bounded by wilting point and porosity. This bounding combined with catchment processes leads to a strong link between spatial variance and spatial mean soil mois- ture, with an initial increase in variance followed by a decrease as mean soil moisture increases from wilting point to saturation. Changes in the spatial control of soil mois- ture and the relationship between soil moisture and terrain also occur as the spatial controls on the soil moisture pattern change in response to mean soil moisture. Strong links between the changes in the spatial characteristics of soil moisture will be demon- strated and the potential of measurements of soil moisture to provide information on catchment state and rainfall-runoff response will be explored.

ABSTRACT Distributed hydrological models employ digital terrain analysis algorithms to provide the spatial discretisation of the terrain in a network of elemental units as well as to define the element terrain attributes and the lateral connectivity among the elements. There are quite a few terrain analysis techniques proposed in the literature. The most commonly applied are contour-based and grid-based techniques. Distributed hydrological models are generally applied with one specific type of terrain analysis technique, although there is no clear evidence that one technique offers better performance than others. We propose that all the terrain-based networks can be characterised within the same general framework and we develop a process based distributed model able to implement any terrain-based network within this framework. We first applied this model to a 1 km^2 catchment in the North Island of New Zealand, implementing a contour-based element network (element area ranging between 50 m^2 and 2250 m^2, with an average value of 300 m^2). We simulated the catchment flow response and soil moisture spatial and temporal dynamics over a period of two years and we tested the model performance against observed flow and soil moisture patterns. We then applied the same model with the same set of parameters, implementing a 25-m grid-based element network, with a multiple-flow-direction algorithm. The simulated flow results are not significantly different, compared to the overall model performance with respect to the observed flow. Larger differences occur in the simulated soil moisture patterns, particularly in the valley areas, where lateral flow is dominant in controlling the local soil moisture. Catchment average soil moisture is significantly higher for the grid approach because the slope computed in the grid-based network is generally lower than in the contour-based network. Simulated soil moisture variance is also much higher for the grid approach because of the greater fragmentation of the flow-paths in the grid-based element network than in the contour-based network. The conclusion is that the type of discretisation can have important effects on the performance of a distributed hydrological model.

Hydrological processes occurring throughout the earth's surface lead to temporal changes in the distribution of mass, which subsequently cause subtle changes in the earth's gravity field. The GRACE mission (Gravity Recovery And Climate Experiment) of NASA and the German Aerospace Centre will provide global data sets of changes in earth's gravity field at unprecedented accuracy over the next several years.

Mismatches in scale between the fundamental processes, the model and supporting data are a major limitation in hydrologic modelling. Surface runoff generation via infiltration excess and the process of soil erosion are fundamentally short time-scale phenomena and their average behaviour is mostly determined by the short time-scale peak intensities of rainfall. Ideally, these processes should be simulated using time-steps of

Application of distributed hydrologic watershed models fundamentally requires watershed partitioning or discretization. In addition to partitioning the watershed into modelling elements, these elements typically represent a further abstraction of the actual watershed surface and its relevant hydrologic properties. A critical issue that must be addressed by any user of these models prior to their application is definition of an acceptable

Phosphorus (P) export from agricultural land contributes to the eutrophication of inland water systems and the development of algal blooms. Phosphorus export between the paddock and farm scales on an irrigated dairy farm in the Macalister Irrigation District, southeastern Australia, was investigated using paddock, farm section and whole farm scale monitoring data. A consistent decrease in P concentrations and loads (ca. 30% decrease in total P) was observed between the paddock and farm section over the study period, while P export from the farm was reduced by up to 98% at the whole farm scale due to installation of a runoff reuse pond. The reduction in P concentrations and loads observed between the paddock and section scales suggests that P does not behave as a conservative solute during transport through the drainage network, at least for the monitored paddocks. The potential for P uptake and release in drains and likely impacts of different management strategies was investigated ...

Estuarine systems such as the Gippsland Lakes (south eastern Australia) have an inherent value, environmentally and to the community through commercial fishing, tourism, recreation and their aesthetic appeal. Phosphorus (P) contributes to eutrophication and the development of algal blooms both in the Lakes and inflowing tributaries which negatively impact on these assets. Irrigated dairy production represents an important P source in some catchments. Of the 230 tonnes of P entering the Gippsland Lakes via Lake Wellington annually, approximately 53 tonnes or 23% is from the Macalister Irrigation District (Grayson and Argent 2002). At a district or catchment scale, drainage networks are a significant pathway for the transport of P and at the catchment scale the drainage networks appear to act as a net sink for P. This paper investigates the effect of farm drains on P transport. Field scale investigations were used to explore the ability of farm scale drains to act as either sources or...

The GRACE (Gravity Recovery and Climate Experiment) mission of NASA and the German Aerospace Centre will provide global data sets of changes in earth's gravity field at unprece- dented accuracy over the next several years. Hydrological processes occurring throughout the earth's surface lead to temporal changes in the distribution of mass which subsequently cause subtle changes in the earth's gravity

Hydrological processes occurring throughout the earth's surface lead to temporal changes in the distribution of mass, which subsequently cause subtle changes in the earth's gravity field. The GRACE mission (Gravity Recovery And Climate Experiment) of NASA and the German Aerospace Centre will provide global data sets of changes in earth's gravity field at unprecedented accuracy over the next several years.

The task of assessing similarity between data sets is common in hydrological modelling. While this has been widely researched for temporal data sets, the similarity between spa- tial patterns has been largely ignored. This has been due to a lack of spatial pattern data. Today there is widespread use of distributed hydrological models and increasing availability of observed spatial patterns.