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United States Department of Agriculture (USDA) 2001

PROCESSES OF SURFACE HYDROLOGY IN THE SEMI-ARID WEST

Surface Hydrology Semi-Arid

United States Department of Agriculture (USDA) Research, Education & Economics Information System (REEIS)

Titre : PROCESSES OF SURFACE HYDROLOGY IN THE SEMI-ARID WEST

Identification : UTA00361

Pays : Etats Unis

Durée : Jul 1, 2001 à Jun 30, 2007

Domaine : Watershed Protection and Management ; Watersheds and river basins, general ;

Partenaire : UTAH STATE UNIVERSITY LOGAN,UT 84322

Objectifs
Identify the temporal and spatial variability of hydrologic pathways, particularly lateral subsurface flow in semi-arid landscapes of the Intermountain West. Initial work in the Cache valley will focus on selecting representative canyon and valley bottom sites. The canyon site will be a zero order (ephemeral stream) basin with a steep slope and shallow soils. It should be similar to an ongoing research near Boise, Idaho, to allow comparison of results. The valley bottom site(s) will be chosen to represent the impact of land-use changes and management strategies on the hydrology of the urban-rural fringe. The objective of this project will be met by testing the following hypotheses. Hypothesis 1. When snow cover is persistent, the soil remains unfrozen and all precipitation infiltrates until the soil surface is saturated, after which overland flow will occur if the precipitation (or snow melt) rate exceeds the infiltration rate. Hypothesis 2. When frozen soil is present, more overland flow will occur prior to saturation, but the relative magnitude of overland flow will depend on the moisture content of the near surface soils at the time of freezing. Hypothesis 3. Infiltrated water will move laterally downslope as unsaturated flow and can be explained by a decline in unsaturated hydraulic conductivity with soil depth due to a persistent decline in moisture content and increase in soil bulk density. Hypothesis 4. Near the base of the slope, lateral flow in the upper portion of the soil column will be dominated by new water, whereas the lower portion of a soil column will be fed by old water from the regolith.

Descriptif
Experiments will be conducted at the hill slope and plot scale, where flow into the reservoirs and conduits along the hydrologic cycle will be quantified by state of the art techniques. Precipitation includes rain and snow melt, with snow melt being the primary source of water for infiltration. It is therefore important to measure both additions to and releases from the water reservoir held in the snow pack. Rain and snowfall will be measured by a weighing bucket gage with a wind shield mounted on a post approximately 1.5 m above the ground surface. Snow depth will be monitored hourly by a sonic depth sensor. Weekly snow surveys will be performed to obtain snow water equivalent. Knowledge of the soil water content and frost status prior to and during high infiltration flux is critical to understanding hydrologic pathways. Volumetric soil moisture content will be monitored by time domain reflectometry in soil pits arranged along a hill slope transect. Thermocouples will record soil temperature as a proxy for frost depth at the same depths as the moisture content sensors. Soil pore water pressure (pressure and tension) will be measured at equivalent locations by pressure transducers with a hydraulic connection to porous ceramic cups. Output from all sensors will be logged hourly to datalogger. A telemetry system will be added to each site to facilitate data acquisition and timely soil water sample collection. A hill slope-scale conservative tracer (KBr) study will test the hypothesis of the predominant hydrologic mechanism at each site. Suction and zero-tension lysimeters will be installed along three transects extending from the channel to the crest of the hill. The lysimeters will be installed to the depth of the lithic contact, or to 1 m. Where the depth to the lithic contact is greater than 50 cm, an additional lysimeter will be installed to a depth of 30 cm. Hydraulic conductivity will be measured at each lysimeter borehole by Guelph permeameter. A line source of KBr will be applied across the slope. Periodic sampling of the suction lysimeters and any collected surface runoff will be analyzed for Br- concentration.

Présentation : USDA

Page publiée le 3 décembre 2015, mise à jour le 29 octobre 2017