Water Resources Professional Project Reports

Document Type

Report

Publication Date

Summer 2021

Abstract

The Middle Rio Grande riparian zone, named the Bosque, provides cultural, aesthetic, environmental, recreational, and historical value to the residents of the Middle Rio Grande valley. Most of the Bosque has not experienced successful native cottonwood (Populus deltoides ssp. wislizenii) recruitment since the completion of the Cochiti reservoir and most of the Bosque cottonwood forest is senescing. This decline of the native species in the Bosque can be attributed to highly managed hydrology of the riparian zone. The levees and agricultural drains managed by the Middle Rio Grande Conservancy District (MRGCD), that borders both sides of the river, also affect the integrity of the Bosque. While the relationship between river stage and ground water level is well understood, the effects of the riverside drains on ground water level and bank storage are less understood. This study uses shallow monitoring well data and river stage data to evaluate the impact of the riverside drains on bank storage, ground water elevation, and the decline of bank storage. These factors affect cottonwood recruitment and native riparian integrity. The study compares the riverside drain on the east side of the San Juan Chama Drinking Water Project diversion dam to the riverside drain on the west, which is shallower, using time series analyses to evaluate the influence the riverside drain has on the native cottonwoods . Comparison of ground water depth measurement from monitoring wells on the west side of the river to those on the east side of the river, installed and monitored by the Bosque Ecosystem Monitoring Program( BEMP), indicate that the agricultural drain and, its induced artificial hydraulic gradient sloping away from the river, is causing the water table to drop below the 3 m at one site, ground water depth where the physiological condition of native cottonwood (decline, resulting in mortality in some individual trees. The agricultural drain has also increased the bank storage decline from a level that promotes optimal growth of cottonwood seedlings of 3 cm/day to a high of 20 cm/day occurring during a high water event in 2017 (Heller 2018).

Keywords

Rio Grande, bosque, cottonwood, riparian

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