Neil Coles

Similarity analysis of runoff generation processes in real‐world catchments

This paper addresses the question of similarity of runoff generation processes between catchments in the eastern wheat belt of Western Australia, and the use of dimensionless parameterizations to quantify this similarity. A spatially distributed rainfall-runoff model, simulating runoff generation by both the infiltration excess (Horton type) and saturation excess (Dunne type) mechanisms, was developed for catchments in the region. Seven small experimental catchments, with field-measured soil hydraulic properties and topography, were used in the study. Following on from the similarity theory developed by Sivapalan et al. (1987), a number of dimensionless similarity parameters were constructed using the field-measured soil and topographic properties, a characteristic length scale, and a characteristic flow velocity. The objective was to determine whether the dominant runoff generation mechanism on a catchment could be reliably predicted by these similarity parameters. This was achieved through sensitivity analyses carried out with the rainfall-runoff model. Two dimensionless parameters, K0* and ƒ*, were found to be critical for characterizing the similarity or dissimilarity of the runoff generation responses between the seven experimental catchments. Within the assumptions of the analysis, two catchments in the wheat belt region can be considered to be hydrologically similar, in terms of their runoff responses, if K0* and ƒ* are identical in both catchments. The dominant mechanism of runoff generation on any catchment can be reliably predicted, provided that the values of K0* and ƒ* are known. A partial quantification of the Dunne diagram (Dunne, 1978) for the wheat belt region, in terms of the infiltration excess and saturation excess mechanisms, was achieved by artificially varying K0* and ƒ* in the rainfall-runoff model to explore the full range of possible runoff generation responses.

Effect of Long-Term Reclamation on Soil Properties on a Coastal Plain, Southeast China

ABSTRACT Wang, L.; Coles, N.; Wu, C., and Wu, J., 2014. Effect of long-term reclamation on soil properties on a coastal plain, southeast China. The coastal plain of Cixi City, in southeast China, has experienced more than a thousand years of land reclamation history. Since 1047, 11 dikes have been built, dividing our study region into 11 zones. The main aim of this study was to evaluate the effects of long-term reclamation on the variability of soil properties. Using an integrated transect and nested sampling approach, a total of 329 surface soil samples were collected. Soil pH, organic matter, electrical conductivity, and particle size distribution were measured. Data were evaluated using classical statistics and geostatistics methods. Results indicate that reclamation exerted quantifiable effects on various soil attributes. There were significant differences in soil properties among the zones. The ranges in semivariograms were approximately equal to or twice the average zone span, suggesting that there was usually a break in continuity of soil properties at the boundary of reclamation zones. As illustrated by the lower nugget effect or larger range distance in semivariograms, soil pH, electrical conductivity, and organic matter similarly showed more continuous patterns in space compared with particle size distribution. With the increase of time since reclamation, salt content, alkalinity, and particle size tended to decrease, while organic matter content tended to increase. Most properties varied greatly in the initial reclamation stages. A relatively steady state was reached within 10 years following the reclamation for pH, about 30 years for organic matter, and 60 years for electrical conductivity, respectively. Further, similar land uses and parent materials produced similar inherent soil properties. These findings can be applied to broader spatial scales in other coastal regions to assist in transitioning from a coastal tidal plain to productive agricultural land, through reclamation, and targeted land management practices.

A Water Yield-Oriented Practical Approach for Multifunctional Forest Management and its Application in Dryland Regions of China†

Mountainous forest areas are vitally important for water supply in dryland regions which suffer from high erosion risk and severe water shortage. Massive afforestation, mainly for erosion control, may reduce the water yield and threaten local water supply security. Moreover, many over-dense forests due to a strict logging ban policy have produced remarkably negative impacts for both forests (e.g., low timber quality, restricted natural regeneration, and high stand instability) and water yield. To satisfy the rapidly increasing demands on water supply and other services, a practical approach for managing forest stands in a multifunctional way, which particularly addresses water yielding, is urgently required. For this purpose, we integrated the existing knowledge and experience, designed an “ideal” stand structure to represent multifunctional forest (MFF) and determined its key parameters (a ground coverage of >0.7, a canopy density around 0.7, and an H/DBH ratio (tree height [m] to the diameter at breast height [cm]) of <0.7). Moreover, a decision process for MFF stand management was recommended as: (1) investigating the site quality; (2) identifying the site-specific main forest functions; (3) quantifying the stand structure; (4) diagnosing the stand structure by comparing with the “ideal” one; and (5) arranging the functions/structure-oriented management measures. In this way, the water-yielding function can be improved and meanwhile other forest functions can be promoted.

How could sensor networks help with agricultural water management issues? Optimizing irrigation scheduling through networked soil-moisture sensors

Irrigated agriculture provides 40% of the Worlds food from 20% of the agricultural land but uses 70% of all global freshwater withdrawals. However, even supposedly efficient and well-managed irrigation systems waste up to 50% of the water applied to the crops under them. Meeting the food needs of an increasing world population from a static or even decreasing land base will, therefore require improved efficiencies in irrigated agriculture and better use of these finite water resources. The first part of this paper reports on a field-based research project which examined a suite of conventional and alternative irrigation systems which were installed at a farm in south west Australia and assessed and compared in terms of their Water Use Efficiency. All “alternative” systems outperformed the conventional surface (flood) irrigation systems with comparative water savings of around 50%. The second part of the paper assesses the potential Water Use Efficiency improvements at farm and system-scales which could be achieved through linking these irrigation systems to wireless soil-moisture sensor networks which are being developed by the authors and which are reported in detail in associate papers. Improving irrigation scheduling and management by better (and, where appropriate, automatic) links to near real-time soil moisture data is shown to produce water savings of up to 30 GL per year at the irrigation system scale.