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About a month and a half later...

Java55 — Wed, 10 Oct 2007 01:12:02 -0400

Like ghosts from the past, stumps which have been submerged from the late 1970's are re-emerging from the waters of Falls Lake at Upper Barton Creek just west of Six Forks Road.

Photo taken October 6, 2007

House Creek Drought Update

Java55 — Mon, 10 Sep 2007 00:01:15 -0400

I made this photo on September 8, 2007 along House Creek between Glen Eden Drive and Lake Boone Trail in Raleigh. In this location is a point where what little water passes through, passes through a crevice in the bedrock lining the bottom of this creek. From what I can tell about 5 gallons per minute was passing through this crevis at this point in House Creek.

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About a half mile downstream along House Creek no water has been passing through for a number of weeks now and the standing pools of water here are drying up. This photo was made just upstream from Blue Ridge Road along House Creek on September 8, 2007. From what I can determine it seems that a combination of wicking towards the dry banks and the drought thirsty trees lining House Creek are soaking up water at a rate currently greater the 5 gallons per minute per half mile!

Silt deposits under Falls Lake exposed

Java55 — Wed, 05 Sep 2007 02:22:08 -0400

Low waters expose the silt deposits at the bottom of Falls Lake
Photo made September 1, 2007

House Creek has quit flowing

Java55 — Wed, 05 Sep 2007 02:13:25 -0400

Just upstream from Blue Ridge Road in Raleigh near Crabtree Valley Mall, House Creek has dried up during the current drought. All that is left are standing pools of water. In all the time I've seen this creek it had never run dry until now. Photo made on September 3, 2007.

Dry Shelley Lake Grass, Minimal Crabtree Creek Flow

mntnlvr — Tue, 04 Sep 2007 11:20:52 -0400

Although Shelley Lake in North Raleigh remains quite full with no outflow, the grass on the south slope of the dam is fried!

Above Picture taken on September 3, 2007.

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At Lassiter Mill, the Crabtree Creek outflow from the dam is minimal. What a difference it makes with the near flooding level of November 2006 shown below.

Above picture taken on September 3, 2007.

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Above picture taken on November 22, 2006.

Scorched

jgmlr1 — Sat, 25 Aug 2007 12:10:46 -0400

I took this picture of a dried plant on a trail in Bond Park. The plant was not guarded by any trees, so it was burned by the sun.

Scorched

jgmlr1 — Sat, 25 Aug 2007 12:10:38 -0400

I took this picture of a dried plant on a trail in Bond Park. The plant was not guarded by any trees, so it was burned by the sun.

Part of a much bigger problem...

Java55 — Sat, 25 Aug 2007 02:32:22 -0400

Here's a link to a recent article from SpaceRef.com which might bring this bigger picture into perspective:

http://www.spaceref.com/news/viewpr.html?pid=23291

Assuming the northern jet stream has been staying stubbornly much farther to our north lately this would imply that there would be less steering currents to move any current weather patterns from west to east as they would have normally been traveling. This in turn would leave people to experience the same type of weather over certain areas for much of the country for much longer periods of time. Something tells me that a lot of folks who have been working upon analysing the global warming situation haven't been paying much mind to BTUs in their calculations. It takes a lot of BTUs to melt 32 degree ice into 32 degree water but when there's less ice to melt there comes a point where global temperatures can no longer be stablized through the BTU interactions created from this melting ice, plus add in the acceleration of positive feedbacks...

...and how many cubic miles of ice has the earth's poles been losing each year, perhaps for centuries if not more? ...and if BTUs aren't going into turning 32 degree ice into 32 degree water then... mud ain't the right word!

Falls Lake average daily water loss Aug. 8-20, 2007

mntnlvr — Fri, 24 Aug 2007 10:06:42 -0400

Good point about the water table and implied wells, let me come back once more with another input.

Falls Lake historical data show that lake elevation dropped one foot (minus 0.01 ft), from 248.24 ft elevation on Aug. 8, 2007, to 247.25 ft elevation on August 20, 2007. This large drop will be a better base for estimating the average daily lake water loss than the daily report provided.

So, we have one foot drop in 12 days on 9200 acres (latest estimate), that's 9200 acre-feet lost, which per day comes to (9200/12) 767 acre-feet, which translates to 250 Million gallons per day.

That still leaves a lot of water unaccounted for, the more so since all the water that flowed into the lake during the period also disappeared! The above daily 250 Mgal. loss assumes no positive inflow.

The daily report on August 20, 2007 showed "only" 66 Mgallons were withdrawn that day for the water supply, so a large volume of water was sent downstream to the Neuse River, evaporated, or infiltrated in the ground. The infiltration may include, as Java55 suggested, a refill of the water table around the lake from which a lot of water is pumped by wells...

So, it looks like not only Raleigh public water use must be drastically cut, but it will take cutting the outflow to the Neuse River, and perhaps restrictions on all well water around the lake, to slow the lake dropping trend.

Better get some good rain soon or we'll all be in deep mud!

Bernard

Don't know if this will help...

Java55 — Thu, 23 Aug 2007 23:23:16 -0400

I don't know if this will help but for every 20 degrees F increase in air temperature, the air's capacity to absorb water vapor doubles, and with lake surface temeratures being relatively high too this can contribute to larger volumes of water being evaporated during at least the daylight hours, but as for those early morning hours... maybe the surface temperture of the lake is still quite high and contributes to increased evaporation during the wee hours of the morning? I don't know for sure but I'm just throwing in a few more variables to be looking at in case you hadn't already looked into those.

Also adding to this, since the water tables in areas surrounding the lake have been dropping, I wonder if anyone knows approximately how much of the lake's water infiltrates into the water table to replenish it in areas surrounding the lake? This might be at least part of the missing water puzzle.

Refined Falls Lake Data Interpretation

mntnlvr — Thu, 23 Aug 2007 22:35:22 -0400

Please, allow me to reply to myself to show from a different set of inputs that similar results can be obtained. Restarting from the Falls Lake daily report for August 22, 2007, there is a large water inflow of 6679 cfs between 1am and 2 am which results in the lake elevation going up by .06 ft. Actually, since there can't be meters on every creek entering the lake, I guess the inflow was figured out from the known lake area and the elevation delta. So, I'll reverse the calculation and figure out the lake area!

6679 cfs adds up to 24,044,400 cf in an hour which raises the lake .06 ft, so dividing the volume by .06 ft, we get an area of 400,740,000 sq ft, that is 9,200 acres, not too far from the 10,000 I used previously which was interpolated from lake area given at low, normal and flood levels.

Now 24,044,400 cf for .06 ft elevation delta correspond to 48,088,800 cf for a change in level of .12 ft, which was the drop between 3 am and the following midnight. Changing the cubic feet to gallons, that drop was a water loss of (rounded up) 360 Million gallons, not too far from the 392 Mgallons of the previous estimate. In fact even more water disappeared because there were a few hours with positive inflow during that period.

Now for the mystery... I still can't reconcile even a 360 Mgallons loss with the outflow given on the daily report, which is a constant 188 cfs for the 24 hours, given a gate at fixed 7.5 in opening. That rate of ouflow on the full 24 hours translates to 121 Mgallons. It is not clear whether the Water supply withdrawn at constant 102 cfs during 24 hours is part of the total outflow. 102 cfs translates to 66 Mgallons in 24 hours (matches well the 65.80 MGD in the report header).

So, at least 360 Mgallons disappeared from the lake from the top level at 3 am until midnight, out of which less than 121 Mgallons went through the outflow gate, less than 66 Mgallons were possibly withdrawn separately for drinking water, 50 Mgallons might have evaporated, that leaves a huge amount of water not accounted for, like 123 Mgallons! The hole is even bigger if the drinking water was already included in the total outflow. A nagging thought, are there other pumps around the lake...? Or, is water going to the Neuse River that was not counted in the outflow? Or was I wrong to pick the high water mark at 3 am as a base for the loss of water for the rest of the day?

I chewed that bone to the marrow, I'll be quiet here for a while!

Bernard

More Falls Lake data

mntnlvr — Thu, 23 Aug 2007 13:08:20 -0400

The UN FAO figures I pulled look like they are indeed based on water, not air, at 20 degrees C or 68 F, which is a key reference temperature for people living by the metric system. However I guess the solar radiation of 15 MJ/day was based on a clear summer day in temperate regions favorable to growing crops. I understand that Falls Lake higher temperature (missing in today's lake report but I guess around 30 C or 86 F) should lead to increased evaporation but high humidity should counter that, with low wind speed being neutral.

More specific Falls Lake information can be found in the daily and historic reports at the site you (Java55) pointed to in another topic:

http://www.saw.usace.army.mil/falls/index.htm

For instance, the lake elevation peaked most recently on April 17. 2007 at 254.69 ft, since going down the drain to end up at 247.25 ft yesterday, August 22, 2007, close to a 7.5 ft drop!

Then, just looking at the latest daily report (midnight to midnight on August 22, 2007), we can see the elevation started at 247. 27 ft, then peaked at 247. 37 ft at 3 am (I guess because of storms or lack of withdrawal), but it still ended up with a loss at 247.25 ft after 24 hours.

Further, 65.8 MGD (I guess Megagalons per day) of water supply were withdrawn in 24 hours, but lake storage at the end was short 175 ac-ft (acres-feet). Darn, where are the cubic meters! Let's translate that one... I usually go to this site for conversions:

http://www.onlineconversion.com/

That says 175 acre-feet correspond to 215,860 cubic meters which again translate to 57,024, 331 US gallons. So 65.8 Mgallons were withdrawn and the lake ended up 57 Mgallons short in 24 hours.

But..., if the 175 ac-ft storage decrease was due to elevation dropping from 247.27 ft to 247.25 ft (.02 ft) in 24 hours, storage lost since the 3 am peak at 247.37 ft is much higher, and that would reflect evaporation, infiltration and dam outflow...

(Update on 8/23/07 at 1 pm)

I realize that extrapolation from a .02 water level drop to one inch of drop may not be reliable, I'll check the reasoning on another day where the stated 24 h storage loss is greater because of a higher level drop.

However, another figure can be based on the level drop of .12 ft or 1.44 inch from peak time at 3 am to the following midnight, and the estimated 10,000 acres of lake area left at this time. That's 14,400 acre-inches of volume which translates to 391 021 719 gallons, or about 392 Mgallons.

So, out of 392 Mgallons lost since 3 am, 66 or less (count started at midnight) was withdrawn for consumption, maybe 50 Mgallons evaporated or infiltrated (see previous append), that leaves 276 Mgallons that went to the drain, or more likely represents the dam outflow to the Neuse River for sustaining wildlife and our neighbors downstream.

The bottom line seems to be that the lake level still dropped in 24 hours despite the inflow, and the dam outflow and lake evaporation combined volume was much larger than the volume of water withdrawn for consumption. So, will conservation in Raleigh make a big difference on slowing the lake level drop at those rates? Maybe it will put the brake a bit on it but not much.

(End of update)

Bernard

These high temperatures aren't helping much

Java55 — Thu, 23 Aug 2007 02:11:17 -0400

I wonder what summer time temperature the UN's Food and Agriculture Organisation was using for a standard from which to do these calculations? That 20 degrees C (or blistering 68 degrees F in merry old England) is certainly not the 40.5 C (or 105 F) like we've had this past Tuesday! (and all those other really hot days these past few weeks).... so I imagine the evaporation rates from this super heated water may have been much greater during these past several weeks or so.

Thanks for the link and info! It does give us some idea of what's going on here.

It's got me to rethinking about the two liter soda bottles I standardly place into my recyle bin each week... maybe I should start refilling them with tap water instead to build up an emergency stockpile of water gradually over time just in case...

Evaporation data

mntnlvr — Wed, 22 Aug 2007 12:20:02 -0400

I forgot the evaporation data for Falls Lake I heard on the news recently, but it was a huge amount. The following web site from the UN's Food and Agriculture Organisation gives some education on evaporation and transpiration (of plants). It shows an evaporation calculation of 4.9 mm of depth per square meter of water loss per day in a lake in summer time, assuming 80 % of solar radiation to the lake results in evaporation.

http://www.fao.org/docrep/X0490E/x0490e04.htm

So, if we round up 4.9 to 5 mm/sq m, or .005 m/sq m, that's .005 cubic meter, or 5 liters per sq meter, or 5 x 10000 per hectare (10000 sq m), that is 50 cubic meters per hectare. From Falls lake data, I estimate the low lake area today at about 10,000 acres. Given approximately 2.5 acres per hectare, lake area would be about 4000 hectares, total evaporation per day could then be 50 x 4000 = 200,000 cubic meters, or about 53,000,000 gallons!

Maybe I heard 47 Million gallons after all..., correct me if I am wrong.

(Update) By the way, Falls Lake data show the lake total area falls dramatically with the drop in lake elevation, which means the lake is quite shallow in many corners.

Bernard (update: sorry, this should have been entered as a reply to Java55 above)

Falls Lake at Upper Barton Creek - August 19, 2007

Java55 — Tue, 21 Aug 2007 21:44:41 -0400

A small Cypress tree stands upon high barren ground above the shore line at the Upper Barton Creek portion along Falls Lake. This photo was taken across Six Forks Road and across the lake from the Upper Barton Creek boat ramp.

Photo taken August 19, 2007

Previously submerged tree stumps now rise above the water at the Upper Barton Creek portion of Falls Lake across Six Forks Road and the lake from the Upper Barton Creek boat ramp.

Photo taken August 19, 2007

An additional note of concern: Considering the amount of surface area which Falls Lake has from which water can evaporate I would hazard to guess that much more water is being evaporated from the lake itself than what little flow of water is still left running into it. (See the Eno River photo taken at the Poet's Walk at Ayr Mount in Hillsborough above for an example.)

How dry is it?

danbarkin — Wed, 15 Aug 2007 16:41:54 -0400

This is Dan Barkin, deputy managing editor of the N&O. We're trying to get a sense of the impact of the drought, and we'd like to enlist local photographers. If your yard (like mine) looks like the Gobi Desert, we'd like you to post your photos with some info about what we're looking at. But it doesn't have to be yards. It could be other impacts of the dry spell.

This is Dan Barkin, deputy managing editor of the N&O. We're trying to get a sense of the impact of the drought, and we'd…