This flood season started off slowly but heavy rainfall this past month has resulted in widespread flooding with some major levels being reached. Our goal is to provide timely and accurate river forecasts and information to our cooperators and partners. We are ready to meet any of the operational challenges that might face us this year.

This issue of the Crawfish Tales will document some of our operational procedures and highlight some changes in our forecast products. A description of the Spring Flood Outlooks is provided in this issue. We are implementing a new forecast point on the Duck River at Centerville, TN (CNVT1) and there will be changes in the flood stage at the Big Black River at West, MS. In this issue, we

are also providing some guidance on preparing for a flood.

We have other development efforts underway. We have began calibrating some of our river basins to improve our model performance and expect a contractor to assist us in this effort. This should result in improved model simulations allowing us to provide improved services to our partners and customers.

Feedback is always welcome. Please let us know if there are additional products or services you need form the LMRFC. We always enjoy hearing from our cooperators and partners.

Each Winter/Spring flood season, the LMRFC prepares and issues a Spring flood potential outlook product describing the potential and relative magnitude for Spring flooding over our river basins. This outlook product considers expected snowmelt, river ice conditions, existing soil moisture and streamflow conditions relative to long term averages, as well as available reservoir flood control stages and future normal precipitation. The outlook also includes any ongoing flooding, along with the current meteorological situation and the National Weather Service 30-day and 90-day precipitation and temperature outlooks over the LMRFC area. Information on flooding potential for the LMRFC area basins includes the lower Mississippi River and its tributaries, as well as all of the Louisiana and Mississippi coastal drainages.

Generally, this seasonal outlook product is first issued during late February and is updated again in mid March. An outlook is issued in April if meteorological and river conditions warrant. The LMRFC releases this outlook to its servicing

Weather Forecast Offices (WFOs) on Thursdays where it is repackaged for dissemination to the public on Fridays. The WFO versions contain flood potential information for their local river basins within their Hydrologic Service Area. Links to the WFO websites can be found on the LMRFC website at: www.srh.noaa.gov/lmrfc/links.shtml.

The primary objective of this product is to provide flood potential outlooks to our servicing WFOs so they can alert the general public to the likelihood for Spring flooding over their local basins. For 2004, the flood potential outlooks covering the entire LMRFC will be issued February 26th and March 11th. A national river flood outlook is scheduled for March 18th and will be released during a press conference hosted by National Weather Service Headquarters.

Yazoo - (ya-’zü). What’s in a name? Although there is no definitive meaning for the term yazoo, the term generally applies to any stream with a belated confluence to the main river. How appropriate, since the Yazoo River slowly meanders parallel to the Mississippi River for approximately 175 miles before joining it. The Yazoo was named by French Explorer René-Robert Cavelier, Sieur de La Salle in 1692.

Figure 1: Yazoo River System in Northern MS

Click for larger image

The Yazoo River, a tributary of the Mississippi River, flows 188 miles from the confluence of the Tallahatchie and the Yalobusha Rivers to the Mississippi River, north of Vicksburg, MS. The basin, an area of about 13,400 square miles, is protected from flooding by an extensive system of levees and reservoirs and covers Mississippi’s northwest. Headwaters for the Yazoo include the Coldwater, Tallahatchie, Yocona, Skuna, Yalobusha, and Big Sunflower sub-basins. The Delta, a fertile plain and major agricultural region, lies between the Yazoo and Mississippi Rivers. This relatively flat plain has a gentle slope and covers the western half of the drainage basin. Flooding in the Delta can occur from rainfall upstream or backwater flooding when the Mississippi River is in flood. The basin’s eastern half is characterized by rolling hills and steep slopes. On average, the Yazoo basin receives 52 inches of annual rainfall, a third of which becomes runoff.

Severe backwater flooding from the record 1927 flood on the lower Mississippi River and disastrous headwater flooding in 1932 and 1933 served as a catalyst for many flood control programs, such as the Yazoo Headwater and the Yazoo Backwater Projects. The Yazoo Headwater project authorized the four lake reservoirs, Sardis, Arkabutla, Enid, and Grenada, with the last completed in 1955. The reservoirs, completed in 1955, control 60% of the hill country runoff and provide a benefit/cost ratio of $2 benefit for every $1 invested.

Reservoir operations by the US Army Corps of Engineers maximize flood control benefits while considering other water resource purposes. Gate are operated to prevent or lessen downstream area flooding. Despite the complex network of levees and reservoirs, flood potential in the Yazoo basin still exists as two lives were lost to the floodwaters last year.

In the spring of 1973, over 20% of the Yazoo basin was inundated from Mississippi River backwater, with some areas saturated for as long as four months. This event caused the record flood for the Sunflower, MS forecast points, as seen in the table below showing all of the forecasted points in the Yazoo basin.