Abbo’s Alley stream in Sewanee flows with stormwater from the recent rains.

Lake Cheston in Sewanee, Tennessee on Nov. 13th.

Rain has finally arrived on the Cumberland Plateau! A total of almost 8 inches of rain fell in Sewanee from the night of Nov. 28th through the morning of Dec. 6th. What impact has this had on the area’s lakes and groundwater?

There has been an increase in lake and groundwater levels in the Sewanee area that may signal that we are moving out of the worst parts of the drought. Much depends on how much rain will fall over the winter. Let’s take a look at the 130 million gallon (mg) Lake Jackson, which serves as Sewanee’s primary reservoir. This lake was 15.1 feet below lake-full levels on October 25th and dropped to 20 feet below lake-full levels on November 26th. On Dec. 7th, after the rains, the lake stood at 19 feet below lake full levels, indicating that the rain has just begun to reverse the decline in the level of this lake. Sewanee removes about 350,000 gallons of water per day from this lake for municipal use. Last year at this time the lake was only 3 feet lower than capacity. In November of 2007 (during the great drought) the lake was  30 feet below lake-full levels, but recovering from an all-time low of 34 feet in October of that year.

Lake Jackson in Sewanee on Oct. 25th at 15 ft. below normal.

Lake Jackson on Nov. 26th at 20 ft. below normal. Red arrow shows level on Oct. 25th.

Lake Jackson is part of Sewanee’s reservoir system, which is administered by the Sewanee Utility District (SUD). Its waters are pumped first into the smaller reservoir of Lake O’Donnell (80 mg), before water is treated at a filtration plant and sent on for public consumption. If the drought becomes severe enough and these lakes become critically low, then water can be pumped into Lake Jackson from nearby Lake Dimmick (230 mg).

Sewanee’s reservoir system. Lake Dimmick can be tapped if levels of other lakes become critically low (mg = million gallons).

On Nov. 17th, SUD estimated that Sewanee had 140 days of water remaining (does not take into account Lake Dimmick). Neighboring Tracy City had 7 months of water left, while Monteagle had yet to make a statement about their days remaining. The Tennessee Department of Transportation closed the Monteagle Interstate 24 rest area during the week to conserve Monteagle’s water.

Other non-reservoir lakes in the area have rebounded slightly. Lake Cheston was 2.3 feet below lake-full levels before the rain and is 1.2 feet low as of Dec. 7th.

Since all groundwater is fed by rain, we are also experiencing record declines in the water table and in the flow of springs. The water level in the well at Snowden Hall on central campus has rebounded 2 feet since the rains (Dec. 7th), but is still 4 feet lower than at the same time last year. Tremlett Spring in Abbo’s Alley was flowing at near record low levels of 6264 gallons per day (down 790 gallons per day in the last four weeks), but has rebounded with the rain to 6451 gallons per day. On the same date in 2007 (during the great drought) Tremlett Spring was producing 6,171 gallons of water per day. For comparison, an average flow rate for the spring is around 12,000 gallons per day.

Even just after the rain, Bridal Veil Falls (which is spring fed) in Sewanee remained a trickle (below).

Bridal Veil Falls in Sewanee remains a trickle on Dec. 1st after 4 inches of rain.

The likely reason that the rain has not raised water levels in lakes and in the ground as much as hoped is that the soil was extremely dry and was therefore able to absorb most of the water that fell. Now, however, it is more likely that any rain falling in the coming weeks will have a greater chance at raising these levels.

This drought has its origins in the early spring of this year. Since March, we have had a total rainfall of just 27 inches. Compare this to 49 inches for the same time period last year and 29 inches during the great drought of 2007. Sewanee has been recording rainfall data since 1896. The driest years on record are 2007 and 1941. This year stands a good chance of becoming one of the driest ever.