Wisconsin River flow will rise from winter low, flood control capacity available

 

Above-freezing temperatures day and night and rain on frozen soil March 13-18 will prodsave as web page

uce runoff to the Wisconsin River and cause a rise in flow as warm air forecast to bathe the 12,000 square-mile drainage basin of the state's largest river will begin to melt away winter's white, cold grip according to Wisconsin Valley Improvement Company (WVIC), Wausau.

 

WVIC is licensed by the Federal Energy Regulatory Commission to operate 21 headwater storage reservoirs for water conservation, flood control and streamflow regulation.

 

Since the Wisconsin flows south, the lower valley typically experiences spring break up before the headwaters portion of the basin in Vilas, Oneida and Lincoln counties.

 

In cooperation with the operators of hydroelectric dams on the Wisconsin River, WVIC also coordinates the routing of high flow on the main stem as it begins to occur below the flood control influence of the headwater reservoirs.

 

The levels having been lowered since January, the large impoundments above the DuBay, Petenwell and Castle Rock dams, from Portage to Adams and Juneau counties, will begin to fill with runoff.  The dams will be operated to reduce the peaks of the high flow that would naturally occur.  Discharge through the generator turbines and flood gates will be metered to allow the filling of the impoundment and the rise in flow below the dam to both occur gradually.

 

A general lack of snow cover on the central and lower basin will allow solar heating to occur and a quicker increase in the rate of melting and runoff.  While melting will occur in the north, 8-10 inches of snow and antecedent cold - it was minus 16 degrees in Oneida County March 9 - will temper the rate of warm up, melting and runoff produced.  Snow, for example, will absorb rain as it ripens to melt.

 

Storage is available for flood control

 

The term flood in river regulation describes an above normal flow event, a rise in flow to above seasonable levels.  Sometimes referred to as freshets, which are sudden rises in flow most often seen after heavy rain, floods occur to varying degrees.  Some are contained by the channel and some spill into flood plains.  The Wisconsin contains well its floods of the most common frequencies, those that statistically occur once every two, five, 10 and 25 years, due to the relatively large size of its channel, flood control through reservoir storage, and flow routing on the central basin.

 

As of the March 9 reservoir report, 78 percent of the storage capacity, or room to contain 13,603 million cubic feet (mcf) of water, was available in WVIC's 21 headwater reservoirs.  Storage available by location in mcf on the river included DuBay 1,494 mcf, Petenwell 2,869 mcf, and Castle Rock 1,538 mcf.  As the supply of liquid water presents itself to the Wisconsin, capacity is available to conserve a total of 19,504 mcf of it.

 

Simply stated, the storage and flow regulation operation of the reservoir system can reduce peak flood flows by 20-30 percent.

  

 

When natural flow rises, winter release cycle will end, refill will begin

 

Water conserved last summer and autumn has augmented natural flow in the Wisconsin River during the winter.  Reservoir water comprised 32 percent of the regulated flow March 9.  Natural flow, the flow that occurs without reservoir operation, had dipped to 979 cubic feet per second (cfs), 53 percent of or 875 cfs less than the 1,854 cfs March normal natural flow as gauged at Merrill.

 

As melting produces runoff and natural flow begins to rise, the winter release cycle will end and the spring refill cycle will begin.  The amount of flow over and above the Merrill and Wisconsin Rapids flow goals will be stored in reservoirs to conserve water and reduce flood flows downstream.

 

 

Wisconsin River flow at winter ebb as melt begins

 

Wisconsin River flow March 13 had reached its lowest rate of the winter compared to normal.

 

 

Weekly average regulated flow was 40 to 72 percent of normal depending on location.

 

Snow March 8 increased headwater snowpack, rain and snow in forecast

 

It took about four hours for six to eight inches of snow to fall on the upper and central Wisconsin River basin March 8.  Melted, the water content amounted to half an inch, or about a quarter to a third of the normal March total.