Clay Center

Overview

The Clay Center site covers 1.53 km² of cultivated cropland in the Republican River basin of north-central Kansas. Relief is gentle (a 19.9 m elevation range at 3 m resolution), so runoff patterns here are controlled less by terrain and more by soil properties: the deep loess soils span hydrologic soil groups B through D, producing a patchwork of infiltration capacities across otherwise uniform fields. That makes Clay Center the benchmark site for the soil-informed workflow (i.e., SSURGO hydrologic groups to curve number to rainfall excess) developed in the Clay Center notebook.

What this site demonstrates:

Soil variability, not topography, drives where runoff concentrates on low-relief agricultural land.
The SSURGO-to-curve-number workflow produces spatially varying rainfall excess that a uniform-rainfall simulation misses.
A ground water scenario suite (seepage during rainfall, seepage only, and springs) on pre-saturated terrain.

Site Details

Location	Clay Center, Kansas
CRS	WGS 84 / UTM zone 14N (EPSG:32614)
DEM resolution	3 m
NAIP year	2021
Area	1.53 km² (170,244 cells)
Elevation	376.69 - 396.57 m (mean 386.71 m)
Average roughness (ARS)	0.13

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. 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	16 Min	20 Min

Discharge - Groundwater seepage in streams, no rainfall

4 Min	8 Min	12 Min	16 Min	20 Min

Depth - Springs

4 Min	8 Min	12 Min	16 Min	20 Min

Discharge - Springs

4 Min	8 Min	12 Min	16 Min	20 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). Coarser grids finish at slightly different steps, so the 10 m map shows step 119.

1 m	3 m	10 m	30 m