September 7, 2008
Three years of lake stratification data.
February 5, 2008
Rule Curve for 2008
Francis E Walter Significant Storage Events and Reference Chart
The chart below shows impoundment data and significant storage events.
January 27, 2007
2006 Francis E Walter Lake Stratification Explained
Pictured above are the water temperature readings collected at various
depths in the Francis E Walter Reservoir (FEW). Personnel from the Philadelphia
District of the Army Corps of Engineers (Corps) collect this data on a
monthly basis during the spring, summer and fall.
The water below the thermocline, known as the hypolimnion, is the region of water that must be sustained, preserved, and gradually released throughout the summer months (approx. 70 days) in order to enhance the wild trout fishery.
Now, take a look at the water temperatures after the June 23rd sampling event. All the coldwater (below 68 Deg F) that was previously present in FEW is gone. Where did it all go??
If you recall, last year at the end of June, our region faced an historic flooding event. FEW filled to 85% of the total flood storage capacity. In accordance with the operations mandate, the Corps was required to release most of the stored water (70% of storage) that was held back to minimize flood damage down river. When the Corps released the water, the largest gates located on the bottom of the lake were utilized to discharge the water at a rate of approximately 8,000cfs. This large blow-out release from the depths of FEW caused the depletion of the coldwater pool. Basically, all the coldwater went down into the Delaware Bay.
As you can see, in order to conserve and preserve this coldwater in FEW,
there mostly likely will need to be modifications to the discharge control
tower. A likely fix will be to retrofit the tower with a port at a higher
elevation on the control tower that is capable of releasing the warmer
water from the top of the lake rather than colder water off the bottom.
This will help to sustain the coldwater pool. But the Corps can't just
do this without doing an in-depth and detailed analysis of the tower and
what releases might look like with tower modifications. To do this, the
Coldwater Study must be completed.
2006 & 2007 Flow Plan Rule Curve (the 2006 Curve was adopted for 2007)
2006 Rule Curve Explained
We have received many questions on how to interpret the Army Corps "Rule Curve" that has been established for this years Flow Management Plan.
For starters, dam operators often use rule curves as a tool to regulate water releases and flows in rivers downstream from a dam.
The lake level behind the Francis E Walter Reservoir is to be raised to an elevation of 1,365' feet above sea level. From May to June there is a restriction on lake level fluctuation by 5 feet. Meaning the lake will not fluctuate more than five feet during this time. This is indicated on the Rule Curve where the "May-June Operating Zone" is indicated on the graph. This restriction is to protect spawning warmwater species in the lake and conserve the coldwater pool in the lake to the extent practical.
The light blue shaded area to the left of the colored lines represents the anticipated amount of storage available in the lake at certain dates. The colored lines represent lake levels at certain times of year. In addition, these colored lines also are used to determine the amount of water to be released from the lake based on inflow and amount of water that is currently stored in the lake. The Corps uses the term Augmentation to illustrate that there will be an intended increase in flow in the Lehigh this summer. The amount of augmentation again depends on the amount of water that is available and inflow to the lake.
To determine the amount of augmentation, the numbers at the bottom of the graph next to the colored dashes determine how much water is going to be released. If you look at the 50/600 numbers, the first number (50) indicates the amount of augmentation that will occur above inflow during non-whitewater release weekends. The second number is the amount of augmentation during whitewater release weekends. So during the week or non-whitewater weekends, if the lake level is at the black line on July 24th, the amount of augmentation above inflow will be 50 cubic feet per second (CFS). So if we have 300 CFS coming into the lake, there should be a 350 CFS release.
However, if the lake is below 1,365' elevation, the amount of flow augmentation will not exceed 250 CFS. For example, if inflow is 220 CFS on July 24th, the flow augmentation will be 30 CFS. If inflow is 300 CFS and the lake is below 1365, the release will remain at 250 CFS until the lake level rises to the next colored line or back up to the 1365 feet elevation, so the Corps will be storing the extra 50 CFS into the lake.
Is this rule curve perfect, the answer is NO. There are some things we think the Corps should consider. If you think about it, the 250 CFS maximum water release limitation is almost as though they are robbing Peter to pay Paul. However, is this a good start and attempt in managing the water .by all means, YES! Will things be changed for the better, you better believe it. The Corps has been very cooperative and in fact they want to learn how to better manage this reservoir as they no have the opportunity to do so.
For questions on this, please send us an email.
Francis E Walter Stratification - 2002 v 2005
This graphic shows a comparison of water temperatures recorded
for the month of June at Tannery during the years of 2002 and 2005.
Tannery is located approximately 6 miles below the FEW. In 2002
the Army Corps raised the lake elevation by 92 feet (1392 ft above sea
level) above normal pool elevation for low flow augmentation to push back
the salt line in the Delaware River at Trenton. In 2005, the Corps
raised the lake by 35 feet (1335 ft above sea level) for recreational