Geology topics

B. Herut

Publications and source records attributed to B. Herut.

4 recordsLinked to original sources

USGS2007

Role of aquifer heterogeneity in fresh groundwater discharge and seawater recycling: An example from the Carmel coast, Israel

A case study is shown in which the pattern of submarine groundwater discharge and of seawater recycling is controlled by local hydrogeological variability. The coastal aquifer in Dor Bay is composed of two units: a partly confined calcaranitic sandstone (Kurkar) and an overlying loose sand. Groundwater in the Kurkar has elevated activities of 222 Rn (∼390 dpm/L) and relatively low 224 Ra/ 223 Ra activity ratios (3–4), while the sand groundwater is significantly less radiogenic (6–90 dpm/L) and shows higher 224 Ra/ 223 Ra ratios. Groundwater discharging from sand-covered areas of the bay has salinities of 16–31 and an average 222 Rn activity of 168 dpm/L, which lies on a mixing line between Rn-rich Kurkar fresh water and Rn-poor seawater. Another key observation is that seawater infiltrates to some extent into onshore sand groundwater, while the fresh water within the submarine Kurkar can be traced up to 40 m offshore. This implies that while fresh water mainly discharges from the Kurkar unit, seawater recycling is limited to the loose sand, and that the discharge from sand-covered areas is a mixture of Kurkar water with recycled seawater. Advection rates from the bay floor were calculated from Rn time series and found to vary between 0 and 36 cm/d, correlating negatively with bay water depth. The average flux was 8.1 cm/d, and it did not seem to change much during March, May, and July 2006. The average amount of fresh water discharging to the bay was 5.0 m 3 /d per meter of shoreline. Radon activity in the sand groundwater also fluctuates due to influx of Kurkar-type groundwater.

Carmel Coast, Dor Bay↗

USGS2007

Remaining uncertainties in the use of Rn-222 as a quantitative tracer of submarine groundwater discharge

Research performed in many locations over the past decade has shown that radon is an effective tracer for quantifying submarine groundwater discharge (SGD). The technique works because both fresh and saline groundwaters acquire radon from the subterranean environment and display activities that are typically orders of magnitude greater than those found in coastal seawaters. However, some uncertainties and unanswered problems remain. We focus here on three components of the mass balance, each of which has some unresolved issues: (1) End-member radon - what to do if groundwater Rn measurements are highly variable? (2) Atmospheric evasion -do the standard gas exchange equations work under high-energy coastal mixing scenarios? And (3) "mixing" losses - are there other significant radon losses (e.g. recharge of coastal waters into the aquifer) besides those attributed to mixing with lower-activity waters offshore? We address these issues using data sets collected from several different types of coastal environment. Copyright ?? 2007 IAHS Press.

Conference Paper↗

USGS2007

Temporal variability of submarine groundwater discharge: Assessments via radon and seep meters, the southern carmel coast, Israel

Seep meter data from Dor Bay, Israel, showed a steady decrease in submarine groundwater discharge (SGD) rates between March and July 2006 (averages of 34, 10.4 and 1.5 cm d-1 in March, May and July, respectively), while estimates based on radon time series showed remarkably uniform averages (8 cm d-1). The May seep meter data show a rough positive correlation with sea level, unlike the negative correlation shown by the Rn-calculated rates. Smaller-size meters, deployed in July adjacent to the regular-size ones, showed significantly higher rates (10 cm d-1), which negatively correlated with salinity. It is suggested that the decreased rates documented by the seep meters are the result of an increased shallow seawater recharge in the bay (due to decreasing hydraulic gradients). This is not captured by the radon, since recharging water is radon-poor. The positive correlation of discharge with sea level is due to increased seawater recycling in times of high sea stand. Copyright ?? 2007 IAHS Press.

Conference Paper↗

USGS2006

Combined time-series resistivity and geochemical tracer techniques to examine submarine groundwater discharge at Dor Beach, Israel

A high-resolution, stationary geophysical and geochemical survey was conducted at Dor Beach, Israel, to examine the shallow coastal hydrogeology and its control on the exchange of submarine groundwater with the shallow Mediterranean Sea. Time-series resistivity profiles using a new 56 electrode (112-m long) marine cable produced detailed profiles of the fresh water/salt water interface and the subtle response of this interface to tidal excursions and other forcing factors. Such information, when ground-truthed with representative pore water salinities and formation resistivity values, can provide unique information of the extent and rates of submarine groundwater discharge (SGD). Time-series 222Rn measurements of the adjacent coastal water column complemented these geophysical techniques and were modeled to yield integrated advective flow rates across the sediment/water interface, which at Dor Beach ranged from about 0 to 30 cm day-1 (mean = 7.1 cm d-1), depending on the tidal range. Such results suggest that the underlying hydrogeologic framework at Dor is favorable for substantial SGD. Extrapolating these SGD estimates across a 100-m wide coastal zone implies that the Rn-derived SGD rate would equal ???7.1 m3 d-1 per m of shoreline, and that the source of this discharging groundwater is a complex mixture of fresh groundwater derived from the upland Kurkar deposits, as well as locally recycled seawater. Copyright 2006 by the American Geophysical Union.

Geophysical Research Letters↗