Frequently Asked Questions
Soil erosion is the movement of soil particles down and from sloping land. These moving soil particles reduce soil productivity and degrade water quality. Soil erosion thins and can completely remove topsoil, the soil layer richest in organic matter and plant nutrient concentration. These lost nutrients must be replaced for crop production purposes, adding extra cost in addition to lost crop yield potential.
The Daily Erosion Project (DEP) estimates soil erosion and water runoff occurring on hill slopes in Iowa and surrounding states. Estimates are based on hill slope conditions (e.g. topography, crop, precipitation) identified via remote sensing tools. From these estimates, the DEP team posts daily estimates of average hill slope soil loss (and water runoff) occurring for each watershed in the DEP coverage area.
WEPP is an erosion prediction model applicable to small watersheds and can simulate up to large fields, mimicking the natural processes important in soil erosion. Everyday it updates the soil and crop conditions that affect soil erosion. When rainfall occurs, the planted crop and soil characteristics are used to determine if surface runoff will occur; then the program will compute estimated sheet, rill, and channel soil erosion detachment and deposition.
A watershed is any land area that channels rainfall and snowmelt to creeks, streams, and rivers, and eventually to outflow points such as reservoirs, bays, and the ocean. A HUC, or hydrologic unit code, is a classification that identifies a watershed by size and location.
Iowa, Nebraska, Minnesota, Kansas, Wisconsin, and portions of China.
Yes! Contact Hanna Bates, Program Coordinator for the Iowa Water Center, and she will arrange a presentation.
As of July 2016, DEP makes over 200,000 WEPP model runs each day. The WEPP model itself is a single threaded job, but thankfully only takes a second to run for the 10+ years we are simulating. Even at a one-second execution time, having 200k runs means that we have to implement some sort of parallel execution to have all the runs complete within a day (only ~100k seconds in a day!).
DEP's goal is to have daily output from the previous day by approximately 6 AM of the current day. This represents a maximum time window of about six hours to accomplish the following tasks:
Update input climate files with yesterday's data
Run the WEPP model 200k times
Process the WEPP output files and create summaries within the database
As of this writing, the DEP processing is done on a Dell PowerEdge R820 with 4 physical processors (48 threads), 256 GB of memory, and two mirrored 1 TB SSD drives. These assets permit the DEP execution to complete by about 5 AM each morning. Ironically, the most computationally "expensive" component of this processing is the input-output associated with the numerous ASCII files used by the WEPP model. The SSD drives allow these small operations to complete with limited latency.
The parallelization happens with a programming script that launches multiple instances of WEPP at the same time. This Python code uses the standard library multiprocessing to proctor the runs. Again, the SDD drives really make this possible as the multiple jobs are not stuck in I/O wait.
The Daily Erosion Project (DEP) uses a tested and proven soil erosion model (the Water Erosion Prediction Project model or WEPP) that estimates soil erosion and water runoff occurring on hill slopes. Estimates are based on hill slope conditions: for example, slope steepness, slope length, tillage used and crop growing in each field, soil type and rainfall. The conditions on each hill slope are identified from remote sensing: LiDAR for topography, satellite imagery for soil and crop management and field boundaries, NEXRAD radar for precipitation, and electronic data bases for details such as soil type. Sheet and rill soil erosion estimates are made for approximately 240,000 randomly selected hill slopes in Iowa with a similar density of hill slope erosion estimates occurring across all of the DEP coverage area. From these DEP erosion estimates, we post daily the average hill slope soil loss (and water runoff) occurring for each HUC12 watershed in the DEP coverage area.