Technical Report

Progress Report on Los Lunas Floodplain Monitoring 2003-2005

URL: https://webapps.usgs.gov/mrgescp/documents/HugoandHorner_2005_ProgressReportonLosLunasFloodplainMonitoring2003-2005.pdf

Date: 2005/01/01

Author(s): Magana H., Horner M.

Publication: Progress report prepared for U.S. Bureau of Reclamation

Abstract:

On June 29, 2001, the U.S. Fish and Wildlife Service (USFWS) issued a Biological Opinion (BO) regarding the effects of certain water management practices upon the Rio Grande silvery minnow (Hybognathus amarus), the southwestern willow flycatcher (Empidonax traillii extimus), the bald eagle (Haliaeetus leucocephalus), the interior least tern (Sterna antillarum), and the experimental-nonessential population of the whooping crane (Grus americana). All are either threatened or endangered species (USFWS 2001). Specifically, the BO evaluated the implications of the U.S. Bureau of Reclamation’s (BOR) discretionary actions related to water management and the U.S. Army Corps of Engineer’s (Corps) water operations rules and nonfederal actions related to ordinary operations on the Middle Rio Grande. The USFWS concluded that these management practices would likely jeopardize the continued existence of the Rio Grande silvery minnow (RGSM) and southwestern willow flycatcher (SWWF) and, therefore, developed a nested set of recommendations, or Reasonable and Prudent Alternative (RPA), that they believe must be implemented in order to avoid a jeopardy condition in accordance with the Endangered Species Act (ESA) 16 U.S.C. 1531 et seq. The Corps and the BOR made an initial determination to accept and implement the general provisions of the RPA.

The Los Lunas, New Mexico Habitat Restoration Project was subsequently initiated and was intended to fulfill the requirement of habitat restoration in the Belen Reach- one of eight reaches in which habitat restoration must be conducted in accordance with Element J of the RPA. Further, it was meant to fulfill the requirement to initiate construction on at least one restoration project within six months from the date of the BO.

The objectives of the Los Lunas project are to improve habitat conditions for the RGSM and SWWF such that in combination with other elements of the RPA a jeopardy condition for the two species could be avoided. In general, the project was formulated to mechanically widen the active river channel and improve adjacent riparian habitats. The design goals of this project were to produce inundation of certain areas in the project area at flows of greater than or equal to 2,500 cfs. The floodplain was lowered to ensure some inundation at a wide range of flows and at flows less than 2,500 cfs. These alterations within the historic floodplain were intended to produce a variety of additional shallow water/low velocity egg-retention and nursery habitats for the RGSM during spring spawning flows. According to the “flood pulse concept” (Junk et al. 1989) the flood pulse is the principal driving force controlling of river-floodplains, and is responsible for the existence, productivity and interactions of the major biota in the river floodplain. Flooding is predicted to trigger an increase in the magnitude of biological processes that occur during both the rising and falling limb of the pulse (Valett et al. 2005). Junk et al. (1989) argue that the overwhelming bulk of the riverine animal biomass derives directly or indirectly from production within the floodplain and not from the downstream transport of organic matter produced elsewhere in the basin.

The Los Lunas site is located on the west bank of the Rio Grande adjacent to Mid Valley Airpark, Los Lunas, New Mexico. Dimensions of the overbank area are approximately 1829 m along the existing riverbank with a generally uniform width of 107 m encompassing an area of approximately 16.2 hectares. The site is bounded on the west by an earthen and rootwad berm approximately two meters high. The greater restoration area suffered a severe fire in April of 2000. As a result, the site offered an exceptional opportunity for restoration as it avoided impacting an intact riparian area.

The goals of this project required a great deal of work and therefore the project was divided into three broadly defined phases. First, approximately 1,400 Kelner jetty jacks (historic flood control/bank stabilization structures) were removed. Second, the excavation of approximately 53,500m3 (70,000yd3 ) of floodplain material would be moved to allow for active channel widening and, accordingly, the creation of more extensive RGSM habitat. Lastly, all areas of terrestrial disturbance were revegetated with native plant species, which should stimulate the process of post-fire reclamation and hopefully lead to a diverse array of higher value riparian habitats. Although temporally separated, the various phases of construction were completed over the following two years. Various forms of monitoring activities are ongoing. This restoration projects differs from others in the inclusion of a long term monitoring program to assess the success or failure of the project.