Biomedical subjects

Steven P Loheide

Publications and source records attributed to Steven P Loheide.

3 recordsLinked to original sources

PubMed2006

Quantifying stream-aquifer interactions through the analysis of remotely sensed thermographic profiles and in situ temperature histories.

The interaction between surface and subsurface waters through hyporheic exchange and baseflow is critical to maintaining ecological health in streams. During warm periods, groundwater-surface water interactions have two primary effects on stream temperature: (1) cool groundwater discharging as baseflow lowers stream temperature and (2) hyporheic exchange buffers diurnal stream temperature variations. We demonstrate, for the first time, how high-resolution, remotely sensed forward-looking infrared (FLIR) images and instream temperature data can be used to quantify detailed spatial patterns of groundwater discharge to a 1.7 km reach of Cottonwood Creek in Plumas National Forest, CA. We quantifythe individual effects of baseflow and hyporheic exchange on stream temperatures by simulating the stream energy budget under different conceptual models of the stream-aquifer interaction. Observed spatial and temporal patterns of stream temperature are consistent with an increase in baseflow and hyporheic exchange within the middle, restored stream reach when compared to groundwater fluxes in the surrounding, unrestored reaches. One implication is that pond and plug stream restoration may improve the aquatic habitat by depressing maximum stream temperatures by > 3 degrees C (K).

Ecosystem↗

PubMedDate not supplied

Hydraulic tests with direct-push equipment.

The potential of direct-push technology for hydraulic characterization of saturated flow systems was investigated at a field site with a considerable degree of subsurface control. Direct-push installations were emplaced by attaching short lengths of screen (shielded and unshielded) to the bottom end of a tool string that was then advanced into the unconsolidated sediments. A series of constant-rate pumping tests were performed in a coarse sand and gravel aquifer using direct-push tool strings as observation wells. Very good agreement (within 4%) was found between hydraulic conductivity (K) estimates from direct-push installations and those from conventional wells. A program of slug tests was performed in direct-push installations using small-diameter adaptations of solid-slug and pneumatic methods. In a sandy silt interval of moderate hydraulic conductivity, K values from tests in a shielded screen tool were in excellent agreement (within 2%) with those from tests in a nearby well. In the coarse sand and gravel aquifer, K values were within 12% of those from multilevel slug tests at a nearby well. However, in the more permeable portions of the aquifer (K > 70 m/day), the smaller-diameter direct-push rods (0.016 m inner diameter [I.D.]) attenuated test responses, leading to an underprediction of K. In those conditions, use of larger-diameter rods (e.g., 0.038 m I.D.) is necessary to obtain kappa values representative of the formation. This investigation demonstrates that much valuable information can be obtained from hydraulic tests in direct-push installations. As with any type of hydraulic test, K estimates are critically dependent on use of appropriate emplacement and development procedures. In particular, driving an unshielded screen through a heterogeneous sequence will often lead to a buildup of low-K material that can be difficult to remove with standard development procedures.

Environmental Monitoring↗

PubMedDate not supplied

Noise in pressure transducer readings produced by variations in solar radiation.

Variations in solar radiation can produce noise in readings from gauge pressure transducers when the transducer cable is exposed to direct sunlight. This noise is a result of insolation-induced heating and cooling of the air column in the vent tube of the transducer cable. A controlled experiment was performed to assess the impact of variations in solar radiation on transducer readings. This experiment demonstrated that insolation-induced fluctuations in apparent pressure head can be as large as 0.03 m. The magnitude of these fluctuations is dependent on cable color, the diameter of the vent tube, and the length of the transducer cable. The most effective means of minimizing insolation-induced noise is to use integrated transducer-data logger units that fit within a well. Failure to address this source of noise can introduce considerable uncertainty into analyses of hydraulic tests when the head change is relatively small, as is often the case for tests in highly permeable aquifers or for tests using distant observation wells.

Artifacts↗