# Matai'an Fan Sediment Dataset — Data Dictionary

The list below outlines the corresponding experimental procedures and the specific physical units used as column headers or data keys in `Mataian_Sediment_Data.[csv / xlsx / json]`.

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## 1. Sampling & Geospatial Information

| Field | Description |
|---|---|
| `Sample_ID` | Unique alphanumeric identifier for each sampling site. |
| `Date_and_time` | Timestamp of field sampling (YYYY-MM-DD HH:MM:SS). |
| `Sampler` | Name of the personnel who collected the sample. |
| `WGS84_Lat` | Latitude in the WGS84 coordinate system (Decimal Degrees). |
| `WGS84_Lon` | Longitude in the WGS84 coordinate system (Decimal Degrees). |
| `twd97_E` | Easting in the TWD97 (Taiwan Datum 1997) projected coordinate system (m). |
| `twd97_N` | Northing in the TWD97 projected coordinate system (m). |

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## 2. Bulk Sample Preparation & Field Moisture

| Field | Description |
|---|---|
| `Bulk_Dish_g` | Weight of the empty container (W1) used for the bulk soil sample (g). |
| `Bulk_Wet_Soil_Dish_g` | Weight of the container plus the wet bulk soil (W2) immediately retrieved from the field (g). |
| `Bulk_AirDry_Soil_Dish_g` | Weight of the container plus the bulk soil (W3) after prolonged laboratory air-drying preparation (g). |
| `Bulk_Apparent_Moisture_pct` | Apparent field moisture content (w), calculated prior to sieving: `[(W2 - W3) / (W3 - W1)] × 100` (%). |

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## 3. Specific Gravity & Hydrometer Calibration

| Field | Description |
|---|---|
| `Specific_Gravity_Gs` | Specific gravity of soil solids (Gs), measured via pycnometer or assigned based on spatial proximity. |
| `Hydro_Sample_AirDry_g` | Weight of the air-dried fine soil fraction prepared for the hydrometer sedimentation test (g). |
| `Hygro_Dish_g` | Weight of the empty weighing bottle used for hygroscopic moisture determination (g). |
| `Hygro_Wet_Soil_Dish_g` | Weight of the weighing bottle plus air-dried fine soil before oven-drying (g). |
| `Hygro_Dry_Soil_Dish_g` | Weight of the weighing bottle plus absolute dry soil (g). |
| `Air_Dry_Moisture_pct` | Hygroscopic moisture content of the air-dried fines (%). |
| `Hydro_Absolute_Dry_Soil_g` | Absolute oven-dry mass of the soil used in the hydrometer test (Ws), corrected as: `[Air-dry mass / (1 + Hygroscopic moisture)]` (g). |

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## 4. Sedimentation (Hydrometer) & Sieve Analysis

| Field | Description |
|---|---|
| `Hydro_Time_min` | Array of elapsed observation times during the hydrometer test (min). |
| `Hydro_Reading` | Array of uncorrected hydrometer readings (R) corresponding to the elapsed times. |
| `Hydro_Temp_C` | Array of suspension temperatures recorded at each hydrometer reading (°C). |
| `Sieve_Opening_mm` | Array of standard sieve opening sizes used in the mechanical sieve analysis for coarse fractions (mm). |
| `Sieve_Retained_g` | Array of the mass of dry soil retained on each respective standard sieve (g). |

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## 5. Particle Size Fractions (by Diameter D)

| Field | Description |
|---|---|
| `Gravel_pct_75_to_4_75mm` | Percentage of Gravel (75 mm > D ≥ 4.75 mm, retained on No.4 sieve) (%). |
| `Coarse_Sand_pct_...` | Percentage of Coarse Sand (4.75 mm > D ≥ 2.0 mm) (%). |
| `Medium_Sand_pct_...` | Percentage of Medium Sand (2.0 mm > D ≥ 0.425 mm) (%). |
| `Fine_Sand_pct_...` | Percentage of Fine Sand (0.425 mm > D ≥ 0.075 mm) (%). |
| `Silt_pct_0_075_to_...` | Percentage of Silt (0.075 mm > D ≥ 0.005 mm, passing No.200 sieve) (%). |
| `Clay_pct_lt_0_005mm` | Percentage of Clay (D < 0.005 mm) (%). |

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## 6. Gradation Curve & Index Properties

| Field | Description |
|---|---|
| `Curve_Size_mm` | Array of merged particle diameters (D) derived from both sieve and hydrometer analyses (mm). |
| `Curve_Passing_pct` | Array of cumulative percent passing corresponding to each particle diameter (%). |
| `D60_mm` | Particle diameter at 60% passing (D60) (mm). |
| `D50_mm` | Median particle diameter (D50) at 50% passing (mm). |
| `D30_mm` | Particle diameter at 30% passing (D30) (mm). |
| `D10_mm` | Effective particle diameter (D10) at 10% passing (mm). |
| `Cu` | Coefficient of Uniformity (Cu = D60 / D10), evaluating the gradation spread. |
| `Cc` | Coefficient of Curvature [Cc = (D30²) / (D10 × D60)], evaluating the gradation symmetry. |

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## Dataset Notes

### 1. Unmeasured Values

Values recorded as `-1` within the arrays indicate that the specific measurement was skipped, unmeasured, or deemed inapplicable for that particular sample.

### 2. Suspended Sediment Samples

Samples **M5g** and **M5h** represent suspended sediment samples collected directly from the river using water bottles. Therefore, they follow a different collection protocol compared to standard bed material samples.

### 3. Specific Gravity (Gs) Assignments

Actual specific gravity measurements (using a pycnometer) were only conducted on representative samples **M1**, **M3a**, and **M5a**. Assuming that nearby sediments share similar physical properties, these measured `Specific_Gravity_Gs` values were assigned to adjacent samples based on spatial proximity as follows:

| Measured Sample | Assigned to |
|---|---|
| M1 | 5, 6A, 6B, 6C, M1, M2 |
| M3a | 1, 2, 3, 4, M3a, M3b, M3c, M4 |
| M5a | M5a, M5b, M5c, M5d, M5e, M5f, M5g, M5h |