Quantification of Longitudinal River Discharge and Leakage in an Alluvial Fan by Synoptic Survey Using Handheld ADV

Ikeda

2013

Hydrogeol J

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Abstract:To determine depth dependence of permeability in various geologic deposits, exponential models have often been proposed. However, spatial variability in hydraulic conductivity, K, rarely fits this trend in coarse alluvial aquifers, where complex stratigraphic sequences follow unique trends due to depositional and post-depositional processes. This paper analyzes K of alluvial-fan gravel deposits in several boreholes, and finds exponential decay in K with depth. Relatively undisturbed gravel cores obtained in the Toyohira River alluvial fan, Sapporo, Japan, are categorized by four levels of fine-sediment packing between gravel grains. Grain size is also analyzed in cores from two boreholes in the mid-fan and one in the fan-toe. Profiles of estimated conductivity, K , are constructed from profiles of core properties through a well-defined relation between slug-test results and core properties. Errors in K are eliminated by a moving-average method, and regression analysis provides the decay exponents of K with depth. Moving-average results show a similar decreasing trend in only the mid-fan above ~30-m depth, and the decay exponent is estimated as ≈0.11 m -1 , which is 10-to 1000-fold that in consolidated rocks. A longitudinal cross section is also generated by using the profiles to establish hydrogeologic boundaries in the fan.

Section: Study Areamentioning

confidence: 99%

Dépendance à la profondeur et modèles exponentiels de perméabilité dans des cônes de déjection graveleux

Ikeda

2013

Hydrogeol J

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“…The median values of the daily mean and drought discharges of this river in the fan were 12.6 and 4.0 m 3 /s, respectively, during the period 1974–2011. Synoptic discharge surveys (Sakata and Ikeda ) revealed that the losing rate Q was about 1 m 3 /s between kilometer point (KP) 15.5 and KP 17.0, where KP is the distance units in kilometers along the river, as shown in Figure . Q was about 80% of the total pumping rate of the city.…”

Section: Methodsmentioning

confidence: 99%

Heat as a Tracer for Examining Depth‐Decaying Permeability in Gravel Deposits

2014

Groundwater

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12Depth dependence of permeability can appear in any geologic setting; however, vertical trends 13 in alluvial gravel deposits are poorly understood because of the high variability of hydraulic 14 conductivity K in monotonic sequences. This paper examines the sensitivity of depth-decaying 15 permeability through heat transport simulation around a river's losing reach in the Toyohira River hydraulic gradient also appears in the observation wells for this analysis, as described below.

“…There are unconfined gravel sequences, which constitute a groundwater reservoir with a total pumping rate of over 80,000 m 3 /d. River seepage is the main source for recharging groundwater (Hu et al 2010;Sakata and Ikeda, 2012), and the filtration process from the river to the deeper levels is controlled by the depth-decaying permeability of gravel deposits on a scale of tens of meters (Sakata and Ikeda, 2013). However, Monte Carlo simulation revealed the importance of heterogeneity on a smaller scale (1 m) for interpreting heat transport between surface water and groundwater (Sakata 2015).…”

Section: Case Studymentioning

confidence: 99%

Analysis of partially penetrating slug tests in a stratified formation by alternating piezometer and tube methods

Imai²,

Ikeda

et al. 2015

Journal of Hydrology

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In partially penetrating slug tests, hydraulic conductivity (K) estimates might not necessarily be valid because of vertical flows in heterogeneous formations. We assess the error in hypothetical stratified formations by numerical sensitivity analysis, and propose an effective method for compensation by incorporating two types of casing configuration (piezometer and tube). The hypothetical stratified formation consists of completely horizontal layers, each 1 m thick; the permeability is different between, but not within, layers. In this study, conductivity estimates in the piezometer and tube methods are calculated by assigning various patterns of conductivity to the test, upper, and lower layers: K T , K U , and K L . The effect of vertical flow becomes significant when K T is small relative to K U or K L , and K L is more important than K U because the base of the borehole is open to the lower formation. The conductivity ratios (estimate over actual value) are treated as approximately linearly dependent on logarithms of K T /K U and K T /K L , so that conductivity estimates can be straightforwardly derived from one piezometer measurement and two tube measurements at the top and bottom of the screen. The linear relations are evaluated and constant parameters are determined under specific conditions. This study also recommends alternating piezometer and tube methods in the drilling procedure because the actual variation of K with depth is larger than that found using isolated measurements, as shown in a field study of alluvial fan gravel deposits in Sapporo, Japan. KeywordsSlug tests, Partially penetrating well, Hydraulic conductivity, Sensitivity analysis, Numerical simulation, Heterogeneity 1．IntroductionSlug tests are employed in both practical engineering and scientific studies to determine in situ hydraulic conductivity, K, by measuring the recovery of head in a single borehole after artificially raising or lowering the water level in the well. Although slug tests are sensitive to artificial and natural conditions in the well (e.g., Black, 2010), they are useful because they are simpler, cost less, and require less equipment than multiple pumping tests. It is also common for slug tests to have a logistical advantage, especially in groundwater contamination investigations. One reason is that slug tests can be conducted without removing or adding water, by lowering a solid piece of metal, called a slug, into a well, which does not disturb the site of suspected contamination. Another reason is that slug test results are related mainly to permeability on a small scale, and thus local information is directly relevant to preferential flow paths for contamination plumes. In addition, a series of slug tests at multiple depths aids in interpreting vertical variations of K.When such vertical profiles are interpolated among different locations, three dimensional distributions of K can be obtained for an individual site. Various previous studies have shown the spatial variability in K obtained from slug test an...