Crawfish Tales

A Quarterly Publication of the National Weather Service Lower Mississippi River Forecast Center
Slidell, Louisiana


All future issues of the LMRFC’s Crawfish Tales will only be posted to our web site.
Please send Dave Reed an email at dave.reed@noaa.gov with the subject “Newsletter
Reminder” to receive a reminder email when our latest issue becomes available online.

David Reed, Hydrologist In Charge Vol. 9No. 2, Spring 2010 Glenn Carrin, Editor


Features
Major Flood on the Ouachita and the Red River Basins Basic River Forecasting Tools Combined Federal Campaign - Outreach at LMRFC

From the HIC

     It’s been several months since the last set of articles. We have had major flooding since the last newsletter and some of the worst flooding occurred during a normally dry time of the year. A couple of our locations have been in flood during the entire period. The article on the recent flooding will provide a brief glimpse of the work and efforts required. We have also highlighted some of the hydrologic tools we use in our forecasting to help you understand some of the difficulties and uncertainties we encounter in providing the forecasts.

     Each year through the Combined Federal Campaign (CFC), the staffs at the LMRFC and the collocated Weather Forecast Office (WFO) have an opportunity to give back to the community. The LMRFC staff donated almost $5,200 to the CFC and exceeded their goal set by CFC. Congratulations to the staffs at both offices for their generosity.

     It has been just announced that the LMRFC and collocated WFO have received the NOAA Bronze Medal for “providing life-saving warning and forecast support during consecutive Hurricanes Gustav and Ike”. I am extremely proud of the efforts of the LMRFC. Congratulations on a job well done and a much deserved award.

     We hope this newsletter will stimulate thought on new and innovative ways our forecasts and products can be used. Feedback on our products and services are greatly appreciated. Please do not hesitate to contact me or any of the staff members with any feedback on how we can improve these vital services to the citizens of the lower Mississippi River Valley.

 

- Dave Reed


Major Flood on the Ouachita and Red River Basins

     During the early Fall of 2009, very heavy rainfall occurred across southern Arkansas and northern Louisiana. A large portion of this area received over 25 inches of rainfall during the period with some areas receiving over 35 inches as shown in Figure 1. This rainfall, 300% to 600% of normal, caused widespread moderate and major river flooding across portions of the Ouachita and lower Red River basins. One location, Bayou Bodcau at Bodcau Lake, reached a new record level. Most of the major river flooding occurred within the Hydrologic Service Areas (HSA) of WFO Shreveport (SHV) and WFO Little Rock (LZK). This particular flood event was notable because the river flooding occurred in October and November, a normally dry period and outside of the traditional flood season from December through May.

                            
Figure 1. Two month rainfall total for Sep-Oct 2009. Pink and white shaded areas exceeded 30 and 35 inches, respectively.

     The above normal rainfall during the Fall of 2009 is typical of a strengthening El Nino in the tropical Pacific which occurred in 2009.

     The initial heavy rain events, which occurred in mid September across southwest Arkansas and north Louisiana, began to saturate the soils and elevate the rivers across the area. The heavy rain was primarily associated with a stationary upper level low pressure system that remained over northeast Texas for several days, channeling a tropical air mass over northern Louisiana and southern Arkansas. 

     With many of the river basins already primed for significant flooding by the September rains, October’s rainfall resulted in widespread moderate to major river flooding. 

     Across the Red River Basin in north Louisiana, a new flood of record was established on Bayou Bodcau at Bayou Bodcau Lake (200.27 ft). On Bayou Dorcheat at Minden, the third highest crest was recorded (24.05 ft). Further downstream at Lake Bistineau, the second highest crest was recorded (147.48). 

     Across the Ouachita River Basin in south Arkansas, the fourth highest crest was recorded at Felsenthal (85.78 ft). In north Louisiana on the lower Ouachita River at Columbia, the third highest crest was recorded (69.3 ft).

     On the following page is Table 1, which provides further details from locations that received significant river flooding.

- Angelo Dalessandro
 
River
Gage location (ID)
Flood Stage
Crest (ft) and Crest ranking
Flood Category
Record crest
Ouachita
Thatcher L&D (CALA4)
79 ft
91.90 ft, 11/2/2009.   6th highest.
Moderate
96.30 feet on 4/6/1945
Ouachita
Felsenthal L&D (FELA4)
70 ft
85.78 ft, 11/9/2009. 4th highest.
Major
88.30 feet on 4/11/1945
Ouachita
Monroe (MLUL1)
40 ft
47.80 ft, 11/10/2009. 8th highest.
Major
50.81 feet on 5/22/1958
Ouachita
Columbia (COLL1)
65 ft
69.30 ft, 11/12/2009. 3rd highest.
Moderate
72.37 feet on 5/5/1991
Bayou Dorcheat
Springhill (SPHL1)
11 ft
20.69 ft, 10/31/2009. 5th highest.
Moderate
22.79 feet on   4/28/1958
Bayou Dorcheat
Minden (Dixie Inn) MNEL1
14 ft
24.05 ft, 11/2/2009. 3rd highest.
Major
25.12 feet on 4/8/1997
Bayou Dorcheat
Lake Bistineau (LBUL1)
142.5 ft
147.48 ft, 11/4/2009. 2nd highest.
Major
147.79 feet on 4/18/1991
Bayou Bodcau
Bayou Bodcau Lake (LBBL1)
172 ft
200.27 ft, 11/5/2009. Record highest.
Major
200.27 feet on 11/5/2009
Table 1. Location, Flood Stage, Crest information, Flood Category, and Record Crest for several flood points during the Fall 2009 flood.

Basic River Forecasting Tools

     In our daily operations, our job is to provide forecasts for rivers in our area to our customers. To make a forecast, our current forecast system must incorporate gage readings, discharge readings and precipitation data into a forecast model. Our models take into account: 1) how much water is flowing from upstream, 2) how much rain has fallen over a basin and how much more is expected, 3) how much runoff is being produced, 4) how much soil moisture is in the basin, and 5) how much water will be routed downstream. Our hydrologic models simulate river discharges and those discharges must be converted to water levels or stages for dissemination to the public

     It is extremely difficult to measure discharge directly; stage can be measured relatively easily. Generally, there is a good relationship between stages and discharge. A plot of this relationship is called a rating curve and an example is shown in Figure 1-1. Because stage data can be measured relatively easily, discharge is computed using a rating curve rather than directly measuring it. Accurately capturing this relationship at any given forecast point is an important key to the river forecast process. The US Geological Survey (USGS) is the federal agency responsible for monitoring the water resources of the country and provide the LMRFC the most current rating curve for most of the river forecast locations.



Figure 1-1 Rating curve of stage (y) versus discharge (x)

     A hydrograph is a graph that shows the change in stage or discharge over time. Figure 1-2 shows a stage hydrograph for a location. With a stage hydrograph we can forecast the time when a certain point on a river will reach its peak flow.

With a rating curve we can forecast what the river stage will be at a particular discharge, and what the river crest may be. 



Figure 1-2 Hydrograph of stage (y) versus time (x)

     How does our forecast model work? Using an estimate of soil moisture, our hydrologic models determine how much rainfall is absorbed into the soil and how much runs off into the rivers. The model also estimates evaporation and allows the soil to dry out simulating natural processes. That runoff is converted to discharge at the stream outlet and is then routed downstream. The forecast model displays a discharge hydrograph of discharges from our model simulations in the past and future along with the discharge hydrograph based on observed stages and a rating curve. That discharge hydrograph incorporates all the flows and rainfall from all locations upstream of the forecast point. Forecasters start at the headwaters upstream and work their way downstream evaluating the hydrographs and making forecasts. 

     The LMRFC is now utilizing a new software program that enables us to rapidly update our forecast models with newly updated rating curves as they become available from the USGS and Army Corp of Engineers. Some rivers that are more active can have rating curves that can be updated daily by the USGS while other rivers can be updated on a monthly basis. An updated rating curve provided by the USGS will usually show a few measurements that have shifted from the previous rating curve. This is just a part of LMRFC’s constant effort to improve our models, forecasts, and services.

- Daniel Pearce

 


Combined Federal Campaign - Outreach at LMRFC

     Each year our collocated offices, the Lower Mississippi River Forecast Center (LMRFC) and the New Orleans/Baton Rouge Weather Forecast Office participate in the Combined Federal Campaign (CFC). The CFC, an annual fundraiser implemented by President John F. Kennedy in 1961, is the only approved charity that can solicit donations from federal employees. The CFC allows federal employees and military personnel to donate to national or local charities through payroll deduction or other methods. Millions of dollars benefit non-profit charities each year through the CFC. 
 

    A wonderful example of how the CFC benefits the local New Orleans area was the contribution of nearly $600,000 to various charities by the federal community following Hurricane Katrina. This is only one indication of how the CFC is the largest and most successful workplace fund-raising model in the world. In 2008, federal employees and military personnel in the greater New Orleans area raised $1.45 million dollars!


       Incentives by the local CFC and local businesses were used to help increase employee contributions and participation. Each employee who contributed was eligible for the incentives. In addition to those incentives, local management also “got into the act”. Historically, local management agreed to perform a silly task if the office reached the monetary or participation goal. This year’s incentive called for the LMRFC Hydrologist-in-Charge (HIC), Dave Reed, to sing karaoke along with Meteorologist-in-Charge (MIC),

Ken Graham. The LMRFC and LIX staffs eagerly contributed to the CFC in order to reach their goals. On December 2nd, both managers sported microphones and performed three karaoke songs in duet in the LMRFC operations area. Staff members were delighted to hear their bosses perform. 


     LMRFC’s very own Dave Reed (left) is joined by WFO New Orleans/Baton Rouge’s Ken Graham for a duet.
Thanks to the support received by LMRFC federal employees, countless men, women, children, and animals will live happier, healthier, more productive lives. LMRFC contributions will also help to meet the greater New Orleans area goal for 2009 of $1.55 million dollars.

-Amanda Roberts

 

 

 


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