#### Paper/Poster/Presentation Title

Creation of a data model to retrieve constrained watershed boundaries.

#### Keywords

Watershed Boundary Flow Direction Grid, Algorithm

#### Start Date

27-6-2018 3:40 PM

#### End Date

27-6-2018 5:00 PM

#### Abstract

When using flow direction grids to describe impacts to streams and watershed pour points two spatial scales of interest are commonly applied, the entire watershed and the local stream catchment. In this presentation we describe an alternative approach referred to as the constrained watershed boundary. Specifically, we define a constrained watershed as a polygon containing all the flow direction grid cells with a surface flow distance less than a prescribed threshold. The proposed algorithm builds upon the HSM algorithm, as described by Haag and Shokoufandeh 2017, and augments the data structure with a flow distance grid calculated directly from the original FDG. The new algorithm allows the rapid retrieval and visualization of constrained watersheds boundaries based on a user defined distance threshold(s).

The merged algorithm is a variant of the HSM algorithm and therefore it will retrieve watershed boundaries more efficiently then grid searching techniques. Empirical tests for the Delaware River Watershed Retrieval problem indicate a reduction from ~35 million read operations to ~45 thousand using the HSM approach Haag and Shokoufandeh 2017.

This algorithm was implemented within a restful-API framework for the continental United States using the 30 m FDG from the NHDPlus v2 (but it can be implemented using any input D8 flow direction grid e.g., Hydrosheds). Results will be demonstrated during the presentation using a standard web browser.

Creation of a data model to retrieve constrained watershed boundaries.

When using flow direction grids to describe impacts to streams and watershed pour points two spatial scales of interest are commonly applied, the entire watershed and the local stream catchment. In this presentation we describe an alternative approach referred to as the constrained watershed boundary. Specifically, we define a constrained watershed as a polygon containing all the flow direction grid cells with a surface flow distance less than a prescribed threshold. The proposed algorithm builds upon the HSM algorithm, as described by Haag and Shokoufandeh 2017, and augments the data structure with a flow distance grid calculated directly from the original FDG. The new algorithm allows the rapid retrieval and visualization of constrained watersheds boundaries based on a user defined distance threshold(s).

The merged algorithm is a variant of the HSM algorithm and therefore it will retrieve watershed boundaries more efficiently then grid searching techniques. Empirical tests for the Delaware River Watershed Retrieval problem indicate a reduction from ~35 million read operations to ~45 thousand using the HSM approach Haag and Shokoufandeh 2017.

This algorithm was implemented within a restful-API framework for the continental United States using the 30 m FDG from the NHDPlus v2 (but it can be implemented using any input D8 flow direction grid e.g., Hydrosheds). Results will be demonstrated during the presentation using a standard web browser.

## Stream and Session

Advanced Methods and Approaches in Environmental Computing

Innovation in Continental Scale Modelling for Decision-making, Research, and Education