Coupling Watershed Erosion Model with Instream Hydrodynamic-Sediment Transport Model: An Example of Middle Rio Grande

1.1 Study area and background The Middle Rio Grande (MRG) is located in Central New Mexico (Figure 1 insert). As one of the most historically documented rivers in the United States, MRG is under constant supervision from regulatory agencies such as the U.S. Bureau of Reclamation (USBR) and U.S. Army Corps of Engineers (USACE) (Albert, 2004). MRG was historically characterized as an aggrading sand bed channel with extensive lateral bank movement, which caused serious flooding problem (Richard et al., 2005; Sixta, 2004). To improve channel conveyance and reduce flood risks, channelization works, levees, and dams were built to control sediment concentrations in the MRG and to inhibit bed aggradation. The reach of this study is the diversion dam reach of the MRG, which spans from Alameda Blvd bridge to Paseo Del Norte bridge including the Calabacillas Arroyo (Figure 1). The diversion dam has been built about 1,500 feet south of the Alameda Bridge on the river. The city of Albuquerque is diverting water from the Rio Grande with the operation of this diversion dam to supplement the city’s drinking water supply. Previously, all of their drinking water needs were supplied by groundwater wells. There are two USGS gauges located at the Alameda Blvd bridge and Paseo Del Norte bridge, respectively. The Calabacillas Arroyo is located in Northwestern Bernalillo and South-central Sandoval counties. The Calabacillas Arroyo is a steep, relatively straight channel with a large widthto-depth ratio and has significant potential for lateral and vertical instability. The channel, consisting of a Bluepoint loamy fine sand, drains a watershed with a total area of approximately 220 square kilometers and enters the MRG about 70 km downstream of Cochiti Dam. The Calabacillas Arroyo watershed is primarily underlain by the sand-rich Santa Fe Formation that is comprised of the basin fill sediments (fluvial, paludal, and lacustrine) of the Rio Grande basin (Simons, Li and Associates, 1983). In addition to the Calabacillas Arroyo watershed, the arroyo also discharges water from portions of the Black’s Arroyo watershed due to contributions from the concrete-lined Black Diversion Channel, the only significant tributary of the Calabacillas Arroyo. The drainage area of the Black’s Arroyo is approximately 25 square kilometers (Mussetter, 1996).