UW Hydrology Study Underway In Holly Collection

April 15th, 2011 by UWBG Horticulturist

Soil test pits indicated by color push pins on map

If any of you have visited the north end of our holly collection in Washington Park Arboretum recently, you probably observed what appears to be a developing wetland. As you may well imagine, standing water where we’re trying to grow healthy hollies just don’t mix very well. See Chris Watson’s post on “Spring Pruning in the Arboretum“.   Why all the standing water? Well, we don’t know.  However, thanks to a collaboration with our School of Forest Resources hydrology professor, Susan Bolton, we may soon have the answers we seek. SFR undergraduate student, Traci Amico, has taken on this investigation as her senior capstone project.  Once we know the source of all the water, we will then be able to plan a viable drainage system that will move the water away from our cherished hollies.  Below is notice for project and will also be posted at site:

  • Notice:  10 soil pits will be dug around the site and monitored on a weekly basis in an effort to determine the source of  flooding in the area.
  • Location:  UW Arboretum, Holly Garden, Lake Washington Blvd and Boyer Ave E
  • Timeframe:  April-May 2011
  • Safety:  Soil pits will be covered and marked with cones

Study Parameters:

I. Soil Pits

a) Data collected from the soil pits will assist in determining soil types and hydrology of the site.

b) After careful consideration of other monitoring processes, soil pits were chosen as the best method for the site because of they are a minimally invasive and relatively inexpensive method of data collection. The pits can be dug with a hand held spade or auger so no heavy machinery will be on the site to further compact the soils. Pits will be dug to no more than 16 inches  and 12 inches in diameter.

c) Pits will be marked with flags and securely covered with plywood to ensure the safety of humans and pets.

d) Exposing soil horizons via soil pits will allow for the visibility of water levels, to ascertain its depth and exposure soil horizons. Monitoring will be done once a week.

e) Suggestions for soil pit locations at the site are below. Google Earth imagery was used.

II. City of Seattle

a) The City of Seattle IT Department has generously offered to let me study   their GIS imagery and plans. With these I will be able to determine the locations of any buried pipes or irrigation and assess the vegetation and hydrology patterns over the years.

III. Google Earth and Aerial Images

a) Google Earth and aerial imaging are both valuable tools in assessing previous vegetation and hydrological patterns at the site due to the historical and 3-D images and ‘real time’ views provided.


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