fix: Add missing river_gauge1.json test model.

pywr-schema/src/test_models/river_gauge1.json

@@ -0,0 +1,66 @@
+{
+  "metadata": {
+    "title": "Simple 1",
+    "description": "A very simple example.",
+    "minimum_version": "0.1"
+  },
+  "timestepper": {
+    "start": "2015-01-01",
+    "end": "2015-12-31",
+    "timestep": 1
+  },
+  "network": {
+    "nodes": [
+      {
+        "name": "catchment1",
+        "type": "Catchment",
+        "flow": {
+          "type": "Constant",
+          "value": -15
+        }
+      },
+      {
+        "name": "gauge1",
+        "type": "RiverGauge",
+        "mrf": {
+          "type": "Constant",
+          "value": 5.0
+        },
+        "mrf_cost": {
+          "type": "Constant",
+          "value": -20.0
+        }
+      },
+      {
+        "name": "term1",
+        "type": "Output"
+      },
+      {
+        "name": "demand1",
+        "type": "Output",
+        "max_flow": {
+          "type": "Constant",
+          "value": 15
+        },
+        "cost": {
+          "type": "Constant",
+          "value": -10
+        }
+      }
+    ],
+    "edges": [
+      {
+        "from_node": "catchment1",
+        "to_node": "gauge1"
+      },
+      {
+        "from_node": "gauge1",
+        "to_node": "term1"
+      },
+      {
+        "from_node": "gauge1",
+        "to_node": "demand1"
+      }
+    ]
+  }
+}