MOE002 - Investigation of Seasonal Hydrology and Variable Source Areas within Regions of Ontario
This project was directly funded by the Ministry of the Environment through the Nutrient Management Joint Research Program. The program supported the development of environmentally effective and scientifically robust management practice options for land application of agricultural and non-agricultural source materials in Ontario.
Please contact Clara Tucker, Water Resources Scientist (Ministry of the Environment) at 416-314-0583 for more information.
Dr. Ramesh Rudra, School of Engineering, University of Guelph
The focus of the research project is to describe various components of seasonal hydrology in Ontario landscapes (stream flow, surface runoff, base flow, and tile flow) and their relationships to physiographic characteristics of the watershed, including soil characteristics, water table depth, depth to an impermeable layer, and topography.
The goal of this project is to develop a cost effective procedure for the identification of variable areas producing runoff and therefore areas of generation of non-point sources of contaminants within the Total Water Contributing Area of a surface drinking water source. The further development of intake protection zones and a P-Index, and identification of multiple farms located in "hot spots' require a methodology identifying which combinations of landscape and soil conditions generate runoff and contribute to recharge and to loadings of nutrients, pathogens and other pollutant to water bodies.
The main components of Ontario hydrology are evapotranspiration (ET), surface runoff (SRO), and sub-surface runoff flows (SSRO) (groundwater, tile, inter/lateral). The major portion of SRO and SSRO enters a stream and is separated as rapid, intermediate (tile/interflow), and slow response (baseflow) of the watershed; however, ET cannot be measured directly. Under Ontario conditions all these components exhibit considerable spatial and seasonal variability. The reviewed literature (approximately 150 articles) focuses on the changes in these responses annually and seasonally by field studies or using modeling tools. Limited studies are available on segregation of stream flow into responses or on a watershed scale for Ontario. A few recent studies have reported impacts of climate change on runoff.
The average annual evapotranspiration (ET) of Ontario is 415 mm which is 57% of total precipitation. ET is higher (> 600 mm) in southern parts of the province as compared to northern parts (< 300mm). Lower surface runoff yields are reported from coarse textured soils compared to fine textured soils. Monthly mean streamflows have significantly increased in March and April in Ontario and also throughout the country. The high amount of runoff and peak flows during late winter and early spring could be due to presence of a frost layer at shallow depth. Studies have also indicated that flooding is not restricted to the spring as generally was the norm in the past. In summary, late winter and spring melt are important runoff contributing seasons, and tile drainage, land cover, and other land management practices have significant impact on Ontario hydrology.
The study developed a computer program to separate baseflow from streamflow, and quantify the baseflow index (BFI, the ratio of baseflow to streamflow) using six different separation methods available in the literature. Since the baseflow indices are arbitrary and true values are unknown, the study evaluated six different separation methods available in the literature: digital filter, UKIH smooth minima, PART, base fixed, base sliding, and local minima for baseflow separation under Ontario conditions. One hundred and sixty-one watersheds, with more than 10 years of streamflow data, were investigated.
Frequency distribution analysis indicated that the digital filter separation method estimated the lowest baseflow and the base sliding method calculated the highest amount of baseflow for all the watersheds, with the UKIH method intermediate. On the annual basis, out of 115 southern, central, and eastern Ontario watersheds, 30 watersheds could be designated as slow response watersheds, and 9 as rapid response watersheds. The remaining 76 watersheds could be classified as intermediate response watersheds. All 46 watersheds in northern Ontario could be classified as slow response watersheds.
Analyses of the annual BFI relationship to physiographic/physical characteristics of the 115 watersheds for south, central and eastern Ontario, indicated that high BFI watersheds have more than 80% well drained soils and a similar percentage of A and B hydrologic soil groups; in contrast, low BFI watersheds are dominated by more than 80% poorly and imperfectly drained soils with a similar percentage of C and D hydrologic soil groups.
The seasonal BFI analysis showed that the estimated baseflow contribution is method dependent. BFI computed by the UKIH and base sliding methods was highest during winter months followed by spring, summer, and fall. However, digital filter method yielded highest BFI values during summer, followed by spring and fall for two physiographic regions.
The analysis of watersheds having a single physiographic feature showed that the BFI and runoff coefficient (RC) were not affected by the area of the watershed and slope class. The BFI and RC are affected by hydrologic soil groups, drainage class, and percent of tile drained area in a watershed. Most of these watersheds are dominantly agricultural but due to lack of precise land use information it was difficult to determine the significance of land use on baseflow.
A set of rainfall simulation field experiments on various hydrologic soil groups (HSG) was completed in 2007 and 2008 to improve the characterization of HSG that are used for runoff generation in many hydrologic models. Experiments also included infiltration tests at the sites and collection of data on soil textural, compaction, and hydraulic characteristics. The rainfall simulation data from previous studies (i.e., SWEEP, Green Plan) were explored to develop a more comprehensive database, but these data were not compatible with the data collected in the field experiments to achieve this objective.
The results from the field experiments indicated wide spatial variability in hydrologic behaviour in the field. The soils in a hydrologic soil group do not show a consistent pattern of hydrologic behaviour. The saturated soil hydraulic conductivity also showed a wide variability within a soil, both within a season and between seasons of the year. The curve number (CN) is used as an index for hydraulic behavior of a HSG and is influenced by soil water content at the beginning of a rainfall event.
A comparison of CN computed from the experimental data using the standard approach to an approach modified for site specific soil moisture content, showed better agreement for summer; however, there was no similarity in original and modified CN values at the same soil moisture levels for fall. The results of the study have highlighted the importance of extensive data on soil properties; therefore, long-term field experimental data, covering various seasons, need to be collected for improved reclassification of hydrologic soil groups.
A cost effective runoff sensor and wireless remote monitoring system (WSN), was developed and evaluated under laboratory and field conditions. The WSN sensors were installed to monitor runoff from eight homogenous fields in a small watershed (4.5 ha) to identify contributing area and flow for 18 rainfall events. A variable source area model to map contributing area was developed, calibrated, and validated. Both the experimental procedure and modeling approach have the capability to map the change in contributing area during a rainfall event.
The results show that the variable source area is highly dynamic in nature. It changes within storm, from storm to storm, and seasonally within the watershed. The factors affecting variable source area vary seasonally; however, soil moisture is the factor that plays an important role in all seasons in initiation of runoff and development of contributing area. For spatially uniform agricultural fields the slope area index (slope/area) may be used to select variable source areas and alternate management options. The results also show that the percentage of the watershed area contributing to runoff during early fall is at a minimum, while it is maximum in spring.
Recommendations relevant to nutrient management
Other projects funded through the Nutrient Management Joint Research Program:
For more information:
Toll Free: 1-888-466-2372 ext. 64554
Local: (519) 826-4554