Vigil Network Site: Cañada de la Cueva Headcut Near Galisteo, New Mexico
Changes Observed from August 19, 1970, to September 12, 1972.
By Harold E. Malde
U.S. Geological Survey, Denver, Colorado 80225
This report provides further measurements made at Cañada de la Cueva at intervals during the period from August 19, 1970, to September 12, 1972. Reference is made to the initial report on this ephemeral stream, based on a survey made on August 17-19, 1970, which was deposited in the Vigil Network file by Richard F. Hadley under covering letter, dated May 21, 1971. The numbering of tables and illustrations which was begun in the prior report is continued here.
The shape of the headcut on Cañada de la Cueva, which was first surveyed on August 19, 1970 (fig. 1) was again surveyed on successive visits, as follows: June 25, 1971; August 2, 1971; August 20, 1972; and September 12, 1972. The position of the headcut at these times is shown in figure 6. The maximum headward retreat of the headcut during this period was 38 feet.
During the successive visits to Cañada de la Cueva, erosion at the headwall was also observed at each of nine erosion pins that had been installed on August 19, 1970. A tenth erosion pin was installed on June 25, 1971, as shown in figure 6. The amounts of erosion recorded at these 10 erosion pins are listed in table 7.
The retreat of the headcut on Cañada de la Cueva was caused by runoff from several rainstorms during the period of observation. The respective discharges and amounts of associated rainfall, as recorded at the U. S. Geological Survey gaging station 1 mile downstream, are listed on table 8.
The discharge from heavy rain on July 19, 1971, caused only a slight amount of erosion at Cañada de la Cueva. A much larger discharge on July 26, 1971, however, caused as much as 11 feet of headward retreat. A roughly equal amount of additional erosion, as determined from a survey made on August 20, 1972, was produced by several episodes of relatively small flow between September 29, 1971, and July 25, 1972. Finally, considerable erosion was again caused by the several periods of moderate discharge between August 25 and September 9, 1972.
From this record, it appears that substantial erosion of the headcut on Cañada de la Cueva can be caused not only by a large discharge, but also by several episodes of lesser discharge that occur over a short space of time. This suggests that frequent rains may soften the alluvium at the headcut and thus make the alluvium susceptible to erosion, even under conditions of small discharge. On the other hand, moderate discharge after a period of prolonged drought (as shown by the storm of July 19, 1971) may cause very little erosion. This suggests that the dryness of the alluvium after a drought may make the alluvium relatively resistant to erosion.
Photographs that were made during the initial survey (figs. 4 and 5) were repeated during the subsequent visits, and three other photo stations were established. A catalog of these photographs accompanies this report (figs. 7-21).
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