Steve Guldan

Deep Percolation and its Effects on Shallow Groundwater Level Rise Following Flood Irrigation

Deep percolation (DP) from irrigation may be important for groundwater recharge in irrigated agricultural river corridors of arid regions, yet few studies of this physiographic setting have characterized both percolation and its direct effects on groundwater levels. The objectives of our study in a sandy loam, flood-irrigated, alfalfa-grass field in northern New Mexico were to (1) compare DP below the 1 m effective root zone based on water balance method (WBM) and Root Zone Water Quality Model (RZWQM) simulations, and (2) characterize effects of DP on shallow groundwater levels. Irrigation water applications were metered, and automated instrumentation measured soil water content and climate data for WBM calculations and RZWQM simulations. Groundwater response was characterized by recorded below-field water levels in four experimental wells. DP varied with initial soil water content and water application amount, ranging from 5 to 18 cm (mean 11.2 ±4.1 SD) with the WBM and from 6 to 17 cm (10.6 ±3.8 SD) with RZWQM (using 0.0005 cm3 cm-3 macroporosity). Across irrigation events, there was high correlation (r = 0.90) between WBM and RZWQM DP. Peak water level response (up to 38 cm) varied from 8 to 16 h after irrigation onset depending on well location and water application amount. Study results show that flood irrigation is a significant source of shallow groundwater recharge. The high correlation between calculated and simulated deep percolation without iterative model calibration indicates that RZWQM can be a useful tool to estimate DP and extend localized field studies to larger spatial scales.

Connectivity of Coupled Hydrologic and Human Systems as the Basis of Resilience in Traditional Irrigation Communities in New Mexico

Changes in land use and water availability are impacting the integrity of traditional irrigation systems and their associated communities worldwide. We designed a study to quantify the components of resilience within coupled hydrologic and human systems in New Mexico USA. We worked collaboratively with three communities in the northern Rio Grande basin to characterize hydrologic, ecological, socio-cultural, land use, and economic system components of linked water and human social systems. Building on component models and quantified resilience examples, we crafted graphical representations of connectivity and resilience. We added data points from around the world gleaned from a research workshop. We found there was more hydrological connectivity with flow paths from irrigation system to irrigated field to groundwater and river; the most important nexus was shallow groundwater recharge. There was more human connectivity with strong connections to land and community involvement; an important nexus was mutualism/social capital. Within the northern New Mexico communities, it appears that hydrological connectivity is associated with higher water availability and even if disconnected due to water scarcity can be restored with renewed water availability. Community connectivity, on the other hand, seems susceptible to long term disruption that self-perpetuates long after the initial stresses are imposed. We compared resilience of the hydrologic and human systems on axes of climate (arid to sub-humid), hydrologic connectivity (between surface water and groundwater and between watershed and river), and community connectedness (between water users and water infrastructure and between community members and water management organizations) including communities from northern New Mexico, Bali, Spain, Morocco, central Chile, Mexico, Ecuador, and southern New Mexico. Hydrologic connectivity was most related to local water availability and climate. Community connectivity seemed to be a function of other variables such as mutualism and local control of governance. Changes in water availability and land use affected communities disproportionately. There appears to be a combination of characteristics that has particularly high resilience: medium aridity allows enough water for hydrologic connectivity yet has enough water scarcity to engender collective community action. Promoting connectivity may be a way to enhance resilience of traditional irrigation communities.