Background
This project builds on a number of related projects on soil erosion and sedimentation in the Lake Winnipeg Basin over the past decade by members of the Project Team.  Through these preceding projects, research and observations clearly indicate that there is great potential to modify sediment management practices within the waterways of the Lake Winnipeg Basin to reduce phosphorus loading to the Lake.

The hydrology of Lake Winnipeg Basin has been highly altered through surface drainage (and flow control).  Over the past 150 years, natural waterways have been deepened, straightened and extended to improve land for agricultural production.  The surface drainage network is very dense and is a predominant feature of the landscape within the Lake Winnipeg Basin, particularly in the Red River Basin.  Surface drainage can take the form drainage ditches to collect runoff from roadways and adjacent land and to convey it downstream.  It can also take the form of in-field surface drains that move water across the land to field edges where the runoff empties into drainage ditches.  Because surface drainage greatly affects the flow and delivery of water, it also affects the transport and delivery of sediments and associated contaminants to Lake Winnipeg.

Over time, waterways used for drainage purposes tend to fill with sediments, a situation exacerbated by vegetation and its capacity to filter sediment.  Sedimentation can be acute where flow is restricted – at the outlets of field surface drains, upstream of culverts used to cross ditches and creeks, and upstream of dams and weirs used to control flow and retain water.  (In ditches, vegetation is the focus of removal because it restricts the flow of water and causes sedimentation, and in removing vegetation, sediments are also removed.) Consequently, the management of sediments in waterways is needed to maintain surface drainage and manage water resources.  Practices to remove and dispose of these sediments are varied and widespread.

To provide some context for this issue: there are about 5,000 sections of agricultural land in the Red River Valley, each with about 10 to 30 surface drain outlets that require sediments to be removed every 3 to 5 years; that is about 25,000 surface drain outlets that are cleaned each year.  Given that these surface drains can run 10 to 100 m into the field, and the length of these drains needs to be cleaned regularly, there is a tremendous amount of sediment removed from in-field surface drains each year.  In the Red River Valley there are also about 1,000 miles of Provincial Roads, 500 miles of Provincial Trunk Highways and thousands of miles of municipal roads that require regular ditch cleaning of sediments and vegetation. 

In these waterways, the effect of sedimentation and vegetative growth on phosphorus dynamics during transport and delivery to Lake Winnipeg are not well understood – the sources and nature of sediment and phosphorus, and the biogeochemical conditions that affect them vary dramatically, both spatially and temporally.  Even less is known about the beneficial and/or detrimental impacts of sediment management practices (removal and disposal).

Objectives:

(i)    to identify and characterize locations within the waterways of the Red River Basin and the Winnipeg River Basin where sediments accumulate (e.g., at the outlets of field surface drains, in the vegetation within ditches, behind weirs, dams and other flow control structures);

(iii)to characterize management practices that affect these sediments and associated phosphorus (management of water levels, removal and disposal of sediments and associated vegetation)

This project will focus on the Tobacco Creek and LaSalle River watersheds in the Red River Basin and in the Catfish Creek and Whitemouth River watersheds in the Winnipeg River Basin.  In addition to a survey of sedimentation and sediment management practices within these watersheds, detailed evaluation of existing and alternative sediment removal and disposal practices will take place at several locations which will be determined during the course of the survey.