create empty gradient barrier table on db setup, tidy gradient barrie…

…r README

model/01_access/gradient_barriers/README.md

@@ -1,32 +1,22 @@
 # Gradient barriers
 
-Generate points at which FWA streams exceed given slope threshold(s) for more than a specified distance.
-Methods are outlined [in the docs](https://smnorris.github.io/bcfishpass/02_model_access.html#generate-gradient-barriers).
+Create and load potential [gradient barriers](https://smnorris.github.io/bcfishpass/02_model_access.html#generate-gradient-barriers).
 
-## Usage
+- gradient barriers are generated at 5/7/10/12/15/20/25/30 percent thresholds, using a 100m minimum length
+- only watershed groups included in `bcfishpass.parameters_habitat_method` are processed/included
 
-To create and load the gradient barrier table:
 
-    make
 
-This tool creates potential gradient barriers at 5/7/10/12/15/20/25/30 percent thresholds, finding slope over 100m. 
-To change the slope thresholds of interest or the interval over which slope is measured, edit `sql/gradient_barriers.sql`.
+## Usage
 
-Note that this tool identifies the locations of *all* potential gradient barriers based on *all* given thresholds. The gradient
-threshold modelled as a barrier for a given species is controlled by the access model query corresponding to that species. 
+To load the gradient barrier table:
 
-## Output table
+    ./gradient_barriers.sh
 
-                         Table "bcfishpass.gradient_barriers"
-              Column          |       Type       | Collation | Nullable | Default
-    --------------------------+------------------+-----------+----------+---------
-     blue_line_key            | integer          |           | not null |
-     downstream_route_measure | double precision |           | not null |
-     gradient_class           | integer          |           |          |
-    Indexes:
-        "gradient_barriers_pkey" PRIMARY KEY, btree (blue_line_key, downstream_route_measure)
-        "gradient_barriers_test_blue_line_key_idx" btree (blue_line_key)
+1. To change the slope thresholds of interest or the length interval over which slope is measured, edit `sql/gradient_barriers_load.sql`.
 
-## Override data errors / note gradient barriers that do not exist
+2. This tool identifies the locations of *all* potential gradient barriers based on *all* given thresholds. The gradient
+threshold modelled as a barrier for a given species is controlled by the access model query corresponding to that species. 
 
-If any gradient barriers need to be removed because they are not present/not barriers, add them to `bcfishpass/data/user_barriers_definite_control.csv`.
+3. If any of the created gradient barriers need to be ignored when modelling (because they are not present/not barriers), 
+add them to `bcfishpass/data/user_barriers_definite_control.csv`.

model/01_access/gradient_barriers/gradient_barriers.sh

@@ -4,8 +4,5 @@ set -euxo pipefail
 PSQL="psql $DATABASE_URL -v ON_ERROR_STOP=1"
 WSGS=$($PSQL -AXt -c "SELECT watershed_group_code FROM bcfishpass.parameters_habitat_method")
 
-# create table
-$PSQL -f sql/gradient_barriers.sql
-
 # load
 parallel $PSQL -f sql/gradient_barriers_load.sql -v wsg={1} ::: $WSGS