SJER

Overview

The San Joaquin Experimental Range (SJER) is a USDA Forest Service experimental range in the granitic foothills of the southern Sierra Nevada, northeast of Fresno. The 0.3 km² study area is oak savanna and annual grassland over shallow, weathered-granite soils, with just 38 m of relief and an ARS of 0.14, gentle terrain, but at 1 m resolution the DEM still captures the low-order swales that organize runoff between scattered oaks and granite outcrops. Together with SFREC it brackets the California rangeland conditions in the ensemble: SJER the gentle, open savanna and SFREC the steeper foothill woodland.

What this site demonstrates:

Flow organization on near-flat rangeland where small swales, not hillslopes, do the routing.
A direct comparison case for SFREC at identical resolution (1 m) with a third of the relief.
The full ground water scenario suite on a small foothill drainage.

Site Details

Location	San Joaquin Experimental Range, California
CRS	NAD83 / UTM zone 11N (EPSG:26911)
DEM resolution	1 m
NAIP year	2022
Area	0.3 km² (295,126 cells)
Elevation	333.12 - 371.12 m (mean 349.67 m)
Average roughness (ARS)	0.14

NAIP Imagery and Derived Products

Geomorphology

1st Order Derivatives

2nd order topographic derivatives

Slope	Aspect	Geomorphon

Profile Curvature	Planform Curvature

Soils

Soil survey polygons come from SSURGO, rasterized by map unit key (MUKEY). The MUKEY raster links every cell to its soil map unit properties (e.g., hydrologic soil group, saturated hydraulic conductivity), which drive the curve-number and infiltration inputs to the simulations below.

SSURGO MUKEY

Simulations

Overland flow is simulated with r.sim.water, the SIMWE path-sampling solution of the shallow-water flow equations. The default run applies a uniform 50 mm/hr rainfall with no infiltration and Manning’s n of 0.1, writing water depth (m) and unit discharge (m³/s) every 2 minutes over a 10-minute event. Spatial patterns therefore reflect terrain routing alone; the ground water and sensitivity sections below relax these assumptions.

Default Parameters

Depth

2 Min	4 Min	6 Min	8 Min	10 min

Discharge

2 Min	4 Min	6 Min	8 Min	10 Min

Ground Water

These runs replace the uniform rainfall input with stream-fed sources derived from flow accumulation, using 500,000 walkers and a 4-minute output step (scripts/groundwater.py). Three scenarios are simulated: groundwater seepage in streams during a 10 mm/hr rainfall, seepage with no rainfall, and springs at first-order streams only. The seepage-only and springs runs reached steady state early and end at 12 minutes; the rainfall scenario runs the full 20. Depth is in meters, discharge in m³/s.

Depth - Groundwater seepage in streams during rainfall

4 Min	8 Min	12 Min	16 Min	20 Min

Discharge - Groundwater seepage in streams during rainfall

4 Min	8 Min	12 Min	16 Min	20 Min

Depth - Groundwater seepage in streams, no rainfall

4 Min	8 Min	12 Min

Discharge - Groundwater seepage in streams, no rainfall

4 Min	8 Min	12 Min

Depth - Springs

4 Min	8 Min	12 Min

Discharge - Springs

4 Min	8 Min	12 Min

Sensitivity Analysis

The sensitivity analysis re-runs the simulation across DEM resolutions of 1, 3, 10, and 30 m and walker densities of 0.25 to 2 walkers per cell, with 10 random seeds per combination and 120 one-minute iterations (scripts/sensitivity.py). The watershed extent is delineated at each resolution with a 30,000-cell accumulation threshold.

Basin extent by resolution

Overlap of watershed extents delineated at 1, 3, 10, and 30 m resolution

Seed-averaged depth by resolution

Mean water depth across the 10 seeds at the final output step of each run (walker density 2). This small basin drains fast, so the runs end at different steps: 30 at 1 m, 120 at 3 m, 70 at 10 m, and 20 at 30 m.

1 m	3 m	10 m	30 m