The state of Canandaigua Lake
By Julie Sherwood, staff writer
Posted May 15, 2011 @ 05:02 AM
Canandaigua, N.Y. —
As businesses and homeowners around Canandaigua Lake hard hit by flash floods finally had a chance this past week to dry out, those concerned with water quality were also busy.
Among those assessing the state of the lake are Canandaigua Lake Watershed Manager Kevin Olvany and Canandaigua Lake Watershed Inspector George Barden. The pair this week inspected some of the hardest-hit areas for erosion, one of the biggest concerns because erosion causes debris and chemicals to wash into the lake. Ongoing efforts to protect water quality and minimize pollution include updating laws controlling lakefront development and educating people about keeping the lake clean.
Olvany answered questions Thursday about recent events and the current state of the lake:
Q. What is the current lake level and how does that compare to what the level typically is this time of year?
The lake level as read by the city of Canandaigua is 689.59 feet this morning (May 12). It is down from its peak of 690.25 from last week. Most years we will see the lake get above 689.00 during the spring, and the mean annual high lake level is 689.40.
Record rainfall totals in April combined with incredible intensity for this time of year generated major runoff from the surrounding watershed, that overwhelmed our ability to release water from the lake to maintain a reasonable lake level. The city has had the gates open almost non-stop since mid-February.
This week the lake level is dropping by about 0.1 feet a day. The forecast does not look great for the weekend and next week so this downward trend will not continue if we get appreciable rains.
Q. What are you finding now in terms of sediment in the lake, and how does this compare with what it typically is at this time?
On May 6, Bruce Gilman (Finger Lakes Community College professor of environmental conservation and horticulture) and I conducted scientific measurements throughout the lake. One of the many measurements we collected is water clarity. We measure this at two stations in the middle of the lake. During the spring, lake clarity is influenced primarily by suspended sediment. Typically, we see water clarity or the depth of light penetration in April to reach approximately 30 feet. On May 6, clarity was only 8.2 feet.
These lake measurements correlate very well with our field observations during the storm events of April 26-27 and May 3. On the 26th, we received three cell bursts of 0.8, 0.6 and 0.6 inches, each lasting approximately 20 minutes. On April 27, Middlesex and other areas in the south end of the watershed received approximately 2 inches of rain in less than an hour. These types of huge “summer thunderstorms” generated tremendous amounts of runoff and occurred on much larger geographic areas of the watershed than is typical.
Based on our field observations of sediment concentrations, lake level increase and our comprehensive sampling program, I estimated that the watershed transported approximately 15-20 million pounds of sediment into the lake during these two days. We have sampled over 50 storm/melt events in the last ten years, and we average about 2 million pounds of sediment for typical storm/melt events sampled. A typical storm is approximately 1-1.5 inches of rain or melt equivalent over a 24 hour period. Therefore, the April 26-27 thunderstorms were equivalent to seven to 10 storms in terms of sediment load coming into the lake.
The major reasons for the difference in sediment load for this storm are the springtime saturated soil conditions, the intensity of the storms and the large geographic area of the watershed that was hit by these storms.
The May 3 storm had us very concerned. We received 1.2 inches of rain. This event occurred over a much longer duration, so the lake level only came up about 4.5 inches. However, if that storm had tracked 100 miles to the west, we could have received an additional 1 to 2 inches of rain, which would have caused substantial stream flooding, increased sediment loads, and the lake would have come up another 7 to 14 inches.
Read more here: http://www.mpnnow.com/ontario_county/x401387223/The-state-of-Canandaigua-Lake?img=3