Erosion Yields in the Arroyo Chavez Basin, Rio Puerco Basin, New Mexico
Allen Gellis, U.S. Geological Survey
Scott Aby, Dixon, NM
Three major channels have cut and filled the Rio Puerco valley in the past
3,000 years (Love and Young, 1983; Love, 1986). Dates in two of these
paleochannels are 2100 B.P. and 625-500 B.P., respectively. An interesting
aspect of these cut-and-fill cycles is that the Rio Puerco channel filled to
the same level in the valley it occupied prior to each cutting event. For
example, by 1880 A.D., the Rio Puerco occupied the same level in the valley it
had before its incision around 600 B.P. (Love, 1986); the Rio Puerco then
incised in 1885 (Bryan, 1925). Recent surveys indicate that the Rio Puerco is
in a cycle of aggradation (Elliott and others, 1998; Gellis and Elliott, 1998)
(fig. 12). This raises interesting questions on what
the sediment source(s) are for this filling and how does the system aggrade;
presumably without a change in base level of the Rio Grande.
To examine possible sources of sediment in filling the Rio Puerco channel, a study quantifying a sediment budget for two subbasins of the Rio Puerco, the Arroyo Chavez (2.21 km2) and Volcano Hill Wash (9.13 km2 ), began in 1995. This paper describes the preliminary results of erosion and sediment yields for the Arroyo Chavez basin.
Topographic Setting
The portion of the Arroyo Chavez basin studied is located in the U.S.
Geological Survey San Luis 1:24000 quadrangle map
(fig.8). Rainfall measured for three years (1985-88) in
the basin averaged 340 mm. A longer record of precipitation, 1941 to 1989,
measured at Cuba, 40 km from Arroyo Chavez was 337 mm. Therefore, annual
rainfall during the period of study were similar to long-term climatic records.
Elevations in Arroyo Chavez range from 1,938 m to 2,021 m. Mesas and slopes are
developed on interbedded sandstones and shales of the Menafee Fm.
Methods
A sediment budget for a drainage basin is based on the amount of sediment
leaving that basin and an accounting of the sources of that sediment
(Dietricht and Dunne, 1978; Swanson and others, 1982). An essential feature of
a sediment budget is defining transport processes, storage elements, and
linkages among the two (Swanson and others, 1982). A sediment budget carried
out by Leopold and others (1966) for an ephemeral drainage outside of Santa Fe,
NM, indicated that channels in most reaches were aggrading. Sheetwash was the
largest source of this sediment accounting for the aggradation. The average
rate of aggradation for all channels was 0.015 meters per year. At this rate
of aggradation, the channel would completely fill to the level of the highest
terrace in 100 to 200 years.
In the Arroyo Chavez basin the transport processes, storage elements, and
linkages were defined for four geomorphic surfaces that describe the basin:
mesa, side slope, fan, and alluvial valley floor (figs.
13 and 14). There are
two alluvial valley floor surfaces: one is adjacent to the main channel, the
other is in a tributary valley containing discontinuous channels. To quantify
the sediment budget, collection of sediment in each element utilized various
techniques (Table 1).
Sediment traps were used to quantify sheetwash and were based on a modified Gerlach Trough (Gerlach, 1967; Gellis, 1998). Sediment traps collected sediment and runoff during rainfall events. The length of the traps were 68 and 85 centimeters (cm) and the depth was 13 cm. To prevent precipitation from entering the trap directly, a lid made of sheet metal was fitted with a hinge to the back of the trap. One to three 1.27cm diameter holes were drilled into the side of the trap, and were connected by tubing to 18.9 liter collection buckets. The traps were installed flush to the ground surface with the opening parallel to the slope contour. The contributing area was bounded with metal edging. At each trap, single-ring infiltration tests were performed.
Sheetwash erosion and deposition was also quantified using nail/washer lines (Leopold and Others, 1966). Fifteen centimeter long nails were driven into the ground with washers placed on the ground surface. Erosion is measured as the increase in distance from the top of the washer to the top of the nail and deposition is measured as the amount of sediment deposited over the washer.
To quantify sediment yields at a larger scale than the sediment traps, straw dams were constructed in 1-2 order channels. At this larger scale, elements quantified in the contributing area to the dams included sheetwash, channel erosion, rilling, piping, gullying, and headcutting. The sediment pool upstream of the dam was dug out and periodically surveyed to quantify sediment volume.
Main channel and tributary erosion were quantified through resurveys of monumented channel cross sections (Emmett, 1965; Gellis, 1998). Bank erosion was measured using bank pins and maximum channel scour was measured using scour chains (Leopold and others, 1966).
To measure flow and suspended sediment, a USGS streamflow gaging station equipped with an automatic suspended-sediment sampler was installed. The automatic sampler was activated by stage and collected samples at set time intervals during a runoff event.
To measure the eolian contribution to the basin, eight collectors were installed. The collectors were 9.5 liter buckets attached to a pole 1.4 meters above the ground. The eolian design followed Reheis and Kihl (1995). A wire mesh was put at the top of the bucket and covered with marbles to mimic the ground surface. The marbles were rinsed during collection and the dust was brought back to the lab for drying.
Results
Preliminary results are only available from the sediment traps, straw dams,
sediment discharge at the streamflow station, and eolian collectors. The
sediment traps and straw dams operated over different time periods. To
normalize for this difference, sediment yields from the sediment traps and
straw dams were calculated by taking the total volume of sediment, in
kilograms, and dividing by the number of days in operation. This value was
divided by the contributing area and multiplied by 365 days, to obtain
sediment yield, in kilograms, per square meter, per 365 days.
Results indicate that the alluvial valley floor immediately adjacent to the main channel has the highest sediment yields, measured at straw dam 5 (5.48 kg/m2/365 days) and sediment traps 5a (3.03 kg/m2/365 days) and trap 5b (1.33 kg/m2/365 days)(Table 2). The alluvial valley floor is a gullied, piped surface with many headcuts working upgradient. Alluviation of the alluvial valley floor dates to about 5100 ybp (calibrated 14C age, Pavich, 1997). A major source of sediment in the Arroyo Chavez basin is this older sediment and as the Arroyo Chavez channel fills it is in a sense cannibalizing itself. The mesa and side slopes surfaces showed the lowest sediment yields ranging from 0.15 to 0.97 g/m2/365 days. The lowest sediment yield recorded for the traps was in trap 6 (0.12 kg/m 2/365 days) located in the tributary alluvial valley floor, a well grassed area.
Sediment yields from the sediment traps and straw dams show an increase in
sediment yield with drainage area to around 300 m2
(fig. 15). Typically,
sediment yield decreases with an increase in area as more sites in the basin
are available for sediment storage (Schumm, 1977; Walling, 1983). Compared to
a river basin scale, the drainage areas of sediment yields quantified in the
sediment traps and straw dams are relatively small and therefore, sediment
storage sites are minimal.
Suspended-sediment discharge measured at the mouth of the basin from October 1, 1996 to September 30, 1997, indicated that 2,350 metric tons of suspended sediment were transported. This amount of transported sediment is analogous to 1.06 kg/m2/yr. Using a value of 1442 kg/m3 for the density of soil, the average values of surface erosion measured from the straw dams and sediment traps range from 0.023 to 2.1 mm per 365 days (Table 2). These values of surface erosion are within values of surface erosion and denudation rates reported for the Southwest, which range from 0.005 mm to 7.3 mm (Table 3). The erosion rates from this study are within denudation rates reported at geologic time scales(>1Ma)(Table 3).
The eolian collectors were sampled three times between July 20, 1996, to March 25, 1998. The total mass sampled for this time period ranged from 1.47 to 3.84 grams (Table 3). The mass of eolian dust was divided by the number of days between collection and multiplying by 365 to obtain an annual rate (g/m2/365 days). This annual rate applied to the area of Arroyo Chavez basin indicates the total eolian contribution would range from 11 to 26.6 metric tons. This value of eolian deposition is 4.7 to 11.3 percent of the total suspended-sediment transported out of the Arroyo Chavez basin from 10/1/1996 to 9/30/97 (2,350 metric tons), and is therefore an important component of the sediment budget.
Summary
The Rio Puerco has cut and filled its channel three times in the last 3,000
years. An important question is what is the sediment source for this channel
fill? To address this question, a sediment budget study was initiated in the
Arroyo Chavez basin in 1995. The objective of the sediment budget was to
quantify rates of erosion and deposition on the main geomorphic surfaces in
the basin: mesa, side slope, fan, and alluvial valley floor. Results are
available for erosion yields measured at straw dams and sediment traps, eolian
flux, and suspended-sediment discharge measured at the mouth of the basin.
A major source of sediment in the Arroyo Chavez basin is the alluvial valley floor adjacent to the main channel which has sediment yields of 1.33 to 5.48 kg/m2/365 days. The alluvial valley floor is an area of gullying, piping, and headcutting. The lowest sediment yield of 0.12 kg/m2/365 days was measured in a tributary alluvial valley containing discontinuous channels. The tributary valley floor is a well grassed area.
Surface lowering rates estimated from the straw dams and sediment traps indicate rates from 0.023 to 2.1 mm/365 days. These values are within rates reported for the Southwest, which range from 0.005 to 7.3 mm. The eolian contribution of sediment to the Arroyo Chavez basin was measured at 7 sites. The eolian flux to the basin ranged from 4.99 to 12.0 g/m2/365 days. This value of eolian deposition is 4.7 to 11.3 percent of the total sediment discharge transported out of the Arroyo Chavez basin and is therefore an important component of the sediment budget.
References
Albrecht, A., Herzog., G.F., Klein, J., Dezfouly-Arjomandy, B., and Goff, F.,
1993, Quaternary erosion and cosmic-ray-exposure history derived from
10Be and 26Al produced in situ-An Example from Pajarito
Plateau, Valles caldera region: Geology, v.21, p.551-554.
Bryan, K., 1925, Date of channel trenching in the arid Southwest: Science, v. 62, p.338-344.
Dethier, D.P., Harrington, C.D., and Aldrich, M.J., 1988, Late Cenozoic rates of erosion in the western Espanola basin, New Mexico--Evidence from geologic dating of erosion surfaces: Geological Society of America Bulletin, v.100, p.928-937.
Dietrich, W.E., and Dunne, T., 1978, Sediment budget for a small catchment in mountainous terrain: Zeitschrift fur Geomorphologie, v. 29, p. 191-206.
Elliott, J.G., Gellis, A.C., and Aby, S.B., 1998, Evolution of Arroyos--Incised Channels of the Southwestern United States: In Thorne, C., ed., Incised Channels, IN PRESS.
Emmett, W.W., 1965, The Vigil Network--Methods of measurement and a sampling of data collected: In, Symposium of Budapest, IAHS Publication no. 66, p. 89-106.
Gellis, A.C., and Elliott, J.G., 1998, Arroyo changes in elected watersheds of New Mexico, United States: In Harvey, M., and Anthony, D., eds., Applying Geomorphology to Environmental Management, A Special Publication Honoring Stanley A. Schumm, Water Resources Publications, LLC, IN PRESS.
Gellis, A.C., 1998, Characterization and evaluation of channel and hillslope erosion on the Zuni Reservation, 1992-95: U.S. Geological Survey Water-Resources Investigation 97-4292, 12 p.
Gerlach, T., 1967, Hillslope troughs for measuring sediment movement: Revue Geomorphologie Dynamique, v. 4, p. 1
Gustavson, T.C., Finley, R.J., and Baumgardner, R.W.Jr., 1981, Retreat of the Caprock Escarpment and denudation of the Rolling Plains in the Texas Panhandle: Bulletin of the Association of Engineering Geologists, v.18, no.4., p.413-422.
Leopold, L. B., W. W. Emmett, and R. M. Myrick, 1966. Channel and hillslope processes in a semiarid area, New Mexico. U.S. Geological Survey Professional Paper :352G.
Love, D.W., and Young, J.D., 1983, Progress report on the late Cenozoic geologic evolution of the lower Rio Puerco: New Mexico Geological Society Guidebook, 34th field conference, Socorro Region II, p. 277-284.
Love, D.W., 1986, A geological perspective of sediment storage and delivery along the Rio Puerco: In, drainage basin sediment delivery, Hadley, R.F., ed., IAHS Publication 159, p. 305-322.
Reheis, M.C. and Kihl, R., 1995, Dust deposition in southern Nevada and California, 1984-1989: relations to climate, source area and source lithology, Jour. Geophys. Res., 100, 8893-8918.
Schumm, S.A., 1977, The fluvial system: John Wiley and sons, 338 pp.
Swanson, F.J., Janda, R.J., Dunne, T., and Swanston, D.N., 1982, Sediment budgets and routing in forested drainage basins: U.S. Department of Agriculture, Forest Service General Technical Report PNW-141, 23pp.
Walling, D.E., 1983, The sediment delivery problem: Journal of Hydrology, v.65, p.209-237.
White, W.D., and Wells, S.G., 1979, Forest-fire devegetation and drainage basin adjustments in mountainous terrain: In Rhodes, D.D., and Williams, G.P., eds., Adjustments of the Fluvial System, Proceedings of the Tenth Annual Geomorphology Symposia Series, Binghamton, N.Y., p.199-223.
