6 BULLETIN 181^ U. S. DEPARTMENT OF AGEIGULTUEE. 
Below the Alabama & Vicksburg Railway bridge tlie river has 
been declared navigable and the landowners are urging the United 
States War Department to improve the condition of the channel. 
There are a great many drifts in this section of the river, and the 
carrying capacity of the stream undoubtedly would be increased if 
its conditions were improved. 
No extensive attempts at drainage have been made in the district 
investigated. One or two property owners have constructed small 
ditches to drain their fields after the floods have receded, and others 
have protected small fields by the construction of levees. 
THE SURVEY. 
In making the survey, base levels were first run along the railroads 
bordering the valley. Bench marks were established at intervals of 
1 mile or less on railroad mileposts or other convenient objects. 
The flood hues or edges of the overflowed land were located by 
compass and stadia. Lines of levels were run across the bottoms at 
intervals of approximately 1 mile, and all of the streams and larger 
sloughs were meandered. Levels were carried on all of these meander 
lines and bench marks estabhshed at intervals of approximately 1 
mil e. Cross sections of the streams and sloughs were taken at frequent 
intervals to determine the sizes and capacities of the channels. 
Soil borings 15 feet deep were taken at intervals of one-half mile 
on the cross hues in order to ascertain the character of* the soil to be 
encountered in excavation. 
Department bench marks were set near a number of the towns, 
their locations being shown on the map (flg. 10), and their eleva- 
tions and locations being given in Appendix I of this report. These 
bench marks consist of iron pipes, 3^ feet long and 3 inches in diam- 
eter, set in the ground to a depth of 3 feet. The top of each pipe is 
covered with a bronze cap on which is stamped ^^ Office Experiment 
Stations, U. S. Dept. Agr. Drainage" and the elevation of the top of 
the bench mark to the nearest foot. All bench marks set were of a 
permanent nature. Those placed on trees were made by cutting a 
notch in the root and driving in a spike, the elevation being taken 
on the head of the spike. A few bench marks were estabhshed on 
bridge piers and tops of culverts. All of these, other than the depart- 
ment bench marks, are inscribed ^^U. S. B. M.," followed by the 
initial of the instrument man and a serial number. Their numbers 
and location are shown on the map and their elevations may be had 
by apphcation to Drainage Investigations. All elevations refer to 
Gulf datum as estabhshed by the United States Geological Survey. 
- Very little time was spent ia locating land lines, and as the original 
corners and lines have practically become obliterated it was necessar}^ 
to tie the survey to known objects, such as railroad mileposts, roads, 
etc. The land liaes shown on the map were obtained by adjusting 
