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| Mature cedar lysimeter site |
The snowpack has now completely melted at all the lysimeter sites, so today we could download the data and make an initial analysis. Total runoff during Dec-13 to Apr-4 was 808mm at the cedar site, and 874mm at the larch site. Actual runoff at the larch site would have been about 40mm greater, as a rain-on-snow event on Dec-24 caused the drainage to back-up resulting in some missing data at the larch site. The reason for the significantly greater runoff at the larch site is the relative lack of canopy interception and evaporation loss under the deciduous canopy. Time-lapse photography showed us that the larch site melt-off was completed on Apr-2, two days earlier than for the cedar site on Apr-4.
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| Daily runoff summary for the cedar and larch lysimeter sites |
The summary chart of daily runoff for the lysimeter sites shown above tells the story of snowpack dynamics in a maritime climate, with frequent runoff events throughout the winter season. However, you can see that the snowmelt runoff begins to increase and become more consistent from the middle of February. The largest runoff events are caused by rain-on-snow on Dec-24 and Feb-12. On Dec-24 the precipitation recorded locally was 59.5mm which is almost the same as the runoff measured at the cedar site. During the main snowmelt season the daily runoff only reaches 20-25mm/day. You can see the hourly runoff values in the chart below, showing peak values of about 2-3mm/hour during fine weather melt, and 4-5mm/hour during rain-on-snow.
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| Diurnal melt pattern in the discharge hydrograph with rain-on-snow events Apr-3 and Apr-6 |
