Dilution is Pollution's Solution - WMG

I spent my Saturday morning on 24rth October, 2009 volunteering for the Watershed Management Group (WMG). WMG had organized an workshop at the 1325 East 8th Street.

WMG was interested in Tucson washes and watersheds. It was currently working in the Rincon Heights neighborhood to provide water quality education ad improvement. Fund for the program was provided by the Arizona Department of Environmental Quality. The major focus of the project was to reduce "non-point source" pollution - that refers to pollution from dispersed sources such as pet waste, grease, households, lawns, sediments, lawn waste etc.

The workshop was intended to empower local residents on adapting Best Management Practices (BMPs) for stormwater quality. The workshop demonstrated on installing bioretention basins, berms, curb cuts and infiltration trenches. Storm water is taken to be an important problem throughout Tucson. The Rincon Heights neighborhood is an area within Campbell at the east, Broadway at the south, Park Ave at the west and the Sixth Street at the north. The area is seen completely inundated during rainfall. So, at various spots WMG had built bioretention basins.

For the basins, we dug ditches of different sizes at 2 ft. distances from the street. Then strong rocks were used to support the wall of the ditches. Water flow towards few ditches was directed through cut curbs.

Ditches - a glance

Some have cut curbs that direct water from streets to flow into the ditch while the other types without cut curbs serve to direct water from side walks.

Ditch with cut curb

Ditch without cut curb

The cut curves are intended just to make small shallow or eddies besides the usual flow of water in streets. In eddies water moves in circular motion thus no danger of scouring as well as it facilitates water retention by the soil on either sides of the street. Care was taken that it does not turn into small channels. These cut curbs were also lined by small rocks so that it can reduce water velocity of the flowing water and thus reduce soil scouring.

Cut curb - to direct water into ditch

While in other ditches water from side walks was directed just by making the surface slopy towards the ditch. When the ditch was ready, it was filled with gravels.

Ditch being filled with gravel

Then we planted plants of different varieties native to Tucson climate. The area gets much drier during the summer and when it rains it gets fully flooded. So, plants were chosen such that they can tolerate temperature extremes of dryness as well as floods. Some of the plants used were Ironwood, Sotol, Humming Bird Trumpet, Flat Top Buckweed, Triangle Leaf Bursage, Ocotillo, Brittle Brush etc.

Dry-loving plants were planted at the upper level and plants adaptive to watery lands were planted at the lower surface in the ditch.

Ditch view after plantation - I

Ditch view after plantation - I

Compost manure was put at the base of every plant to facilitate growth. The ditch was then completely covered by mulch up to 4-6 inches to reduce evapotranspiration.

Mulch Cover

This kind of ditches/bioretention basins are made up of locally available natural resources, cheap to construct and people do not need special knowledge or skill to work for it. So, it is highly useful and in turn reduces erosion by storm water. Storm water as well as surface water when get directed to small ditches while flowing through the main street during heavy rain, it reduces water velocity and thus its strength to carry soil on its way. Besides, the storm water gets re-directed towards the ditches before reaching their respective wash. The wastes instead of getting deposited in the wash, are diluted to different areas from where they are absorbed by the ground. This facilitates retention through the soil surface and thus helps in reducing the extent of pollution as well. If the wastes end up in the washes, it would obviously increase the pollution concentration but absorption of wastes at different ground surface facilitated by the eddies has diluted the pollution.

I joined the workshop to get introduced with a group working in watershed issues. The workshop helped me learn the rainwater harvesting technique practically which we usually read in books and lectures. If there is a will, we can make our way locally and easily wihout any bigger investment. It was great fun working with them. I look forward for working with the WMG again in future !!

Activities by WMG can be accessed from here.