12 Transactions Texas Academy of Science. [44] 
near the bottom that will reduce the deposition of silt somewhat. How- 
ever, the area of such gates wilL necessarily be small in comparison with 
the cross section of the . reservoir, so that the velocity through the body 
of the lake will be small, and considerable deposition must take place. 
If the location and cost permit it will be effective, for a time, to con- 
struct settling reservoirs above the storage reservoir proper, in which 
the bulk of the silt will be deposited, and as these fill up others may be 
constructed or the heights of dams raised. This latter expedient may 
sometimes be employed with the storage reservoir itself, and I have been 
informed by Mr. Wentworth Conduit, manager of the Tlahuaiilo 
hacienda, near Torreon, Mexico, that this is sometimes done in the inte- 
rior of that republic. At Carlsbad, New Mexico, a storage reservoir was 
constructed in 1889 and 1890, and the dam failed in 1893. Professor 
W. M. Peed, of Eoswell, has written me that at this time the deposit in 
the lake averaged three feet in depth, notwithstanding the water of the 
Pecos river carries a smaller average amount of silt than is carried in 
the waters of other streams upon which such reservoirs have been pro- 
jected. In 1893, another storage reservoir was constructed ten or 
eleven miles higher up the Pecos and the old one repaired. Since that 
time the deposit in the lower lake has been little or nothing, the silt 
being caught in Lake McMillan — the upper reservoir. During 1899 the 
water in Lake McMillan got quite low, and Mr. Reed made some inves- 
tigations on the depth of deposit. Close to the dam he found about 
sixteen inches of silt, and this increased regularly toward the upper end, 
ten miles above, where it was about four feet deep. Mr. Reed made his 
measurements by simply digging through the mud where it had been 
exposed by the fall in the lake level. 
Col. E. S. Nettleton, formerly State Engineer of Colorado, has kindly 
given me the results of some of his observations, in Spain and Mexico, 
regarding silt removal from existing reservoirs. A portion of this I 
condense for use here: The Alicante dam in Southern Spain is one 
hundred and thirty-five feet high, being thrown across a narrow, rocky 
gorge only about twenty-five feet wide at the bottom. The reservoir 
extends for about 1.25 miles above the dam. The feeding stream is 
small, and the actual capacity of the reservoir is only about 3000 acre 
feet. The sides of the reservoir being very steep, the bulk of the silt is 
deposited in the old channel at the bottom of the reservoir — the most 
favorable arrangement possible for sluicing. At the very lowest por- 
tion of the dam there is a sluicing opening about six feet wide and eight 
feet high, closed by 12x12 timbers), set upright, with another set laid 
cross-wise of the others. The whole is supported by heavy posts set 
inside the gallery, and these are suddenly removed when it is found 
necessary to empty the reservoir. When this is done the opening is 
quite large in comparison with the cross-section of the reservoir, and 
