Measuring I&I in Kodiak, Alaska

Kodiak Island is famous for huge Kodiak brown bears, world-class sport fishing, one of the largest commercial fishing ports in the nation, and the magnificent green that the island turns during the summer--which is why Kodiak is affectionately called Alaska's Emerald Isle.

Aside from its beauty, Kodiak is also a thriving business community, a transportation hub for southwest Alaska , and home of the largest U.S. Coast Guard base in the country.

The City of Kodiak âs Public Works Department is the supplier of water and sewer services in and around the city. The cityâs population, according to the 2000 census, was 6,334 out of the entire Kodiak Borough population of 13,913, making it the seventh largest city in Alaska in terms of population.  In an ongoing effort to comply with EPA regulatory permitting requirements, the city needed to identify, quantify and reduce the amount of inflow and infiltration entering their system.  

Infiltration is groundwater or stormwater that enters the sanitary sewer through cracks, holes and open pipe joints. During rainfalls, the water table may rise above the elevation of the sanitary sewer, allowing the water to surround the pipe and find its way in. Inflow is storm water that enters the sanitary sewer system directly from cross-connection with the storm water, from storm water collectors such as roof drains or catch basins, or from ponding over manhole covers.  Inflow and infiltration can overload both the sanitary sewer and the treatment plant. Storm water runoff generally doesnât need to be treated and it is considered a waste of treatment capacity to design or enlarge plants to accept it. Comparisons of wet weather flows versus dry weather flows are made to determine the extent of the I/I.  Flow monitoring of I/I is considered the least costly investigative technique for the amount of information gained.

A consulting engineering firm was initially contracted by the city to do the I&I work.  However, it soon became apparent to the cityâs engineering staff that it would be more cost effective for them to perform their own flow studies.  Another reason for this was the fact that the studies performed by the consultants did not always fit the timeframes of the weather events the city needed to monitor.  Although Alaska does have its cold spots, Kodiak Island lies on the southern coast of Alaska and has a very moderate climate.  Snowstorms will very often turn into large rainstorms due to Kodiakâs Alaskan gulf location. An average of 68 inches of rain and 65 inches of snow fall on Kodiak Island annually.  

The city made the decision to purchase two Marsh-McBirney Flo-Tote Open Channel Flowmeters for their I&I studies. The Flo-Tote flowmeter is a portable electromagnetic flowmeter that calculates flow utilizing velocity and area (depth) data to calculate flow. The electromagnetic sensor/band assembly is easily installed in the open channel. The flow data is collected by the sensor and stored in the electronics compartment for later data retrieval.

According to Chuck Tripp of the Public Works Department, the two Flo-Tote portable flowmeters are moved from site to site throughout Kodiak City âs sanitary sewer system.  Wet and dry weather flow data collected by the Flo-Tote is  compared to determine the location and quantity of I&I.  Thus far, the city has been able to determine that several leaking manholes in their system were in need of structural repair.  The city plans to annually budget funds for ongoing I&I projects throughout their sanitary sewer system in an effort to continually reduce their I&I flows.