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Impoundments: Downstream Impacted Zone

The impoundment influence zones layer is created using a network analysis methodology that maps a user-specified length downstream from an impoundment. The impoundments layer comes from the DSL Project version of The Nature Conservancy's dam inventory with locations snapped to the NHD high resolution flowlines. The impoundment influence zones are uploaded to the SHEDS database and used to identify sites that are potentially influenced by upstream impoundments.

Data Sources

Layer Source
Dams Shapefile UMass Land Ecology Lab - DSL Project
NHD High Resolution Flowlines Conte Ecology Group - NHDHRDV2

Shapefile Creation

Steps to Run:

The folder structure is set up within the scripts. In general, the existing structure in the repo should be followed.

  1. Open the script createImpactedZones.py

  2. Change the values in the "Specify Inputs" section of the script

  • baseDirectory is the path to the folder where results are written
  • hydroRegions is a list of the hydrologic regions to process
  • zoneDistanceM is the distance downstream, in meters, of each dam to cover
  • snapDisancetM is the maximum snapping distance, in meters, from the raw impoundments layer to the flowlines
  • sourceImpoundments is the file path to the impoundments layer
  1. Run the script in ArcPython

Process Description:

The processing of this layer may be difficult to follow. This description
is intended to assist with replication and re-use of the script. The different sections of the script are outlined separately.

Network Pre-processing

This section maps the impoundments within the specified snap distance to the flowlines and creates a layer of the stream segments with dams present for processing. Only the dams where the column "Use" = 1 are processed. These dams have been confirmed to be on the high resolution flowlines.

Linear Referencing

This section creates the routes layer and determines the position of each impoundment along the stream segments.

The FMEAS column indicates the location along the segment, in meters, where the impoundment falls. The FMEAS column is used to create the line representing the impacted downstream zone from the impoundment.

A zoneM field is added for specifying the location along the segment, in meters, of the end point of the route event calculation. The calculation method varies for confluence and non-confluence zones described below.

When an impoundment falls on a confluence the marked location may slightly exceed the length of the line, resulting in a blank feature when generating the impacted zone. This situation is corrected by setting FMEAS to be 1 meter less than the length of the line, creating a small false section. These false sections are created so the processing will continue downstream from the confluence without stopping due to blank features. This effectively includes the case with the "Conlfuence Points" described below. These sections are removed later.

Non-confluence Points

This section handles the impacted downstream zones that do not contain any confluences. This is the simpler of the processing methods.

In this section, zoneM is calulated as the impoundment's position along the line plus the specified zone distance (zoneDistanceM).

Confluence Points

This section handles locations that have 1 or more confluences in the impacted downstream zone (zoneDistanceM).

The script iterates through confluences until the specified zone distance is met. A new field named totalZoneM is added to track the length of the zone as it is mapped iteratively through confluences from segment to segment. The zoneM field ends up being incremental and either equals the total length of the segment or the length that will push the total zone length (totalZoneM) to the specified zone distance. The FMEAS column is calculated as 0 for any segments directly downstream of a confluence.

At the end of the section all of the non-confluence and confluence zones are merged into a single layer with the aforementioned 1 meter correction sections bing removed.

Join Connected Areas

After merging the segments some connected reaches may still exist as separate features. This section converts the connected zones into single features by utilizing small buffers around each line segment. Overlapping buffers signify common groups by which the lines are joined into single features.

Impacted Catchment Pour Points

A separte list of catchments with pour points falling within an impounded zone is generated. These catchments are identified when the catchment boundary is crossed by an impoundment impacted zone and the catchment contains a dam. The possibility of false positives exist in the cases where the inlet of the stream segment into the catchmet is the point of crossing and a dam (with downstream zone) exist within the catchment without crossing the boundary at the pour point.

Output Layers

Impacted Zones

Layer name: impoundedZones[zoneDistanceM]m.shp
Description: This polyline layer represents the sections along the flowlines that are within the specified distance downstream of an impoundment.

Pour Points

Table name: impactedPourPoints[zoneDistanceM]m.dbf
Description: This table identifies the catchments with pour points falling within the specified distance downstream of an impoundment.

Database Upload

The impoundment zone shapefile created in the previous section is uploaded to the SHEDS database. The upload script is specific to the zone shapefile with the reference to the spatial object being hard-coded, meaning a new script will need to be derived for each new zone length (a simple task). For example, the import_impoundment_zones_100m.sh script directly references the impoundedZones100m.shp layer. The steps below follow the example of the 100 meter zone.

  1. Save the impoundment zone shapefile into a dedicated folder on the server with the name identifying the zone length (e.g. impoundedZones100m.shp). The upload script will specifically reference this name. The existing layer is currently saved to the /home/kyle/data/gis/impoundment_zones directory on felek.

  2. Set parameters for the bash script import_impoundment_zones_100m.sh.

  • Parameter 1: The name of the database
  • Parameter 2: The path to the directory containing the impoundment zone shapefile A duplicate of the script in this repo is saved in the /home/kyle/scripts/qaqc directory on felek.
  1. Execute the bash script in the command line:
  • ./import_impoundment_zones_100m.sh sheds_new /home/kyle/data/gis/impoundment_zones
  1. The layer is uploaded to the specified database as the gis.impoundment_zones_100m table.

QAQC Process

The uploaded layer is used to identify sites in the database from the public.locations table that are potentially influenced by impoundments. An optional CSV indicating the locations to check may be used with the script. The format of this CSV is an integer column with the header 'id'.

  1. Set parameters for the bash script id_impoundment_sites.sh.
  • Parameter 1: The name of the database
  • Parameter 2: The path to the output directory
  • Parameter 3: The path to the optional input CSV
  1. Execute the bash script in the command line:
  • Evaluate all locations: ./id_impoundment_sites.sh sheds_new /home/kyle/qaqc

  • Evaluate specified locations: ./id_impoundment_sites.sh sheds_new /home/kyle/qaqc /home/kyle/qaqc/eg_check_locations.csv

  1. A CSV identifying the sites within the downstream zone of an impoundment is saved to the output directory. The file has one column with the header "id". Currently, the identification method uses a 10 meter buffer around the site locations to determine if they intersect with an impoundment zone. This is because the points are not snapped to the flowlines.

Next Steps

  • Upgrade the catchment pour point selection method.