Determination of infiltration and percolation rates along a reach of the Santa Fe River near La Bajada, New Mexico

Two methods, one a surface-water method and the second a
ground-water method, were used to determine infiltration and
percolation rates along a 2.5-kilometer reach of the Santa Fe
River near La Bajada, New Mexico. The surface-water method uses
streamflow measurements and their differences along a stream reach,
streamflow-loss rates, stream surface area, and evaporation
rates to determine infiltration rates. The ground-water method
uses heat as a tracer to monitor percolation through shallow
streambed sediments.

Data collection began in October 1996 and continued through
December 1997. During that period the stream reach was instrumented
with three streamflow gages, and temperature profiles were
monitored from the stream-sediment interface to about 3 meters below
the streambed at four sites along the reach.

Infiltration is the downward flow of water through the stream-
sediment interface. Infiltration rates ranged from 92 to 267
millimeters per day for an intense measurement period during June 26-
28, 1997, and from 69 to 256 millimeters per day during
September 27-October 6, 1997. Investigators calculated
infiltration rates from streamflow loss, stream surface-area
measurements, and evaporation-rate estimates. Infiltration rates
may be affected by unmeasured irrigation-return flow in the
study reach. Although the amount of irrigation-return flow was none
to very small, it may result in underestimation of infiltration
rates. The infiltration portion of streamflow loss was much greater
than the evaporation portion. Infiltration accounted for about
92 to 98 percent of streamflow loss. Evaporation-rate estimates
ranged from 3.4 to 7.6 millimeters per day based on pan-evaporation
data collected at Cochiti Dam, New Mexico, and accounted for about 2
to 8 percent of streamflow loss.

Percolation is the movement of water through saturated or
unsaturated sediments below the stream-sediment interface.
Percolation rates ranged from 40 to 109 millimeters per day during
June 26-28, 1997. Percolation rates were not calculated for the
September 27-October 6, 1997, period because a late summer flood
removed the temperature sensors from the streambed. Investigators
used a heat-and-water flow model, VS2DH (variably saturated, two-
dimensional heat), to calculate near-surface streambed
infiltration and percolation rates from temperatures measured in the
stream and streambed.

Near the stream-sediment interface, infiltration and
percolation rates are comparable. Comparison of infiltration and
percolation rates showed that infiltration rates were greater
than percolation rates. The method used to calculate infiltration
rates accounted for net loss or gain over the entire stream reach,
whereas the method used to calculate percolation was
dependent on point measurements and, as applied in this study,
neglected the nonvertical component of heat and water
fluxes. In general, using the ground-water method was less labor
intensive than making a series of streamflow measurements and relied
on temperature, an easily measured property. The ground-water method
also eliminated the difficulty of measuring or estimating
evaporation from the water surface and was therefore more direct.
Both methods are difficult to use during periods of flood flow. The
ground-water method has problems with the thermocouple-wire
temperature sensors washing out during flood events. The surface-
water method often cannot be used because of safety concerns for
personnel making wading streamflow measurements.