LWI Region 3 Modeling Overview

3.5 SOIL DATA PROCESSING AND INTEGRATION 3.5.1 Soil Data - Parameter Selection and Processing For all Region 3 watersheds, soil parameters were selected based on the Deficit and Constant Loss method, as outlined in LWI's June 2021 Modeling Guidance. This approach simulates how soil absorbs and retains water before contributing to runoff ( Figure 3-15).

THE KEY PARAMETERS USED ARE: Initial Deficit: Represents the soil’s moisture deficit at the start of a storm event. To simulate realistic antecedent conditions, models are initialized three days after a prior rainfall, allowing the soil to drain to field capacity. The value varies by event and is typically expressed as a percentage of the maximum soil deficit. Maximum Deficit: Represents the soil’s total water holding capacity. Parameter was calculated using effective porosity minus wilting point storage over the assumed active soil depth. Active Soil Depth: Refers to the depth of soil that actively participates in runoff processes. Based on rooting depth research, an initial depth of 24 inches (in)was used, adjustable during calibration.

Hydraulic Conductivity: Defines how quickly water moves through saturated soil. Regionwide, values were assigned based on Rawls (1982) soil data. This parameter set helps ensure a consistent and regionally appropriate representation of infiltration behavior across all hydrologic models developed in Region 3. Table 3-1 presents the initial and maximum soil deficits along with hydraulic conductivity values. The calculations are shown in the report section. The initial deficit serves as a placeholder and is adjusted as a percentage of the maximum deficit, depending on the antecedent soil saturation for each specific storm event.

Table 3-1 Soil parameters used in the model. Initial deficit varies by event based on antecedent conditions.

HYDRAULIC CONDUCTIVITY (INCHES/ HOUR)

TEXTURE

MAXIMUM DEFICIT (INCHES)

4.64 1.18 0.43 0.13 0.26 0.04 0.04 0.02 0.01 0.01 0.063

9.768 9.048 8.472 8.232 8.904 5.952 6.336 6.264 5.496

Sand

Loamy Sand Sandy Loam

Loam

Silt Loam

Sandy Clay Loam

Clay Loam

Silty Clay Loam

Silty Clay

4.92 4.32

Clay

Made Land

0

0

Water

43.3 0.02

9.12

Gravel Pit

5.496

Sand

Initial Deficit is used a % of Max deficit, dependent on the modeled historical storm event

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LWI REGION 3 TRAINING

LOUISIANA WATERSHED INITIATIVE