feat(MacroRugo): implementation of Ferguson equation

Refs #346

src/macrorugo/macrorugo.ts

@@ -287,8 +287,11 @@ export class MacroRugo extends FishPass {
             const reynolds = this.U0 * this.prms.Y.v / MacroRugo.nu;
             return 0.3164 / 4. * Math.pow(reynolds, -0.25);
         } else {
-            // Equation (3) (Cassan et al., 2016)
-            return 2 / Math.pow(5.1 * Math.log10(Y / this.prms.Ks.v) + 6, 2);
+            // Ferguson equation proposed in Cassan et al. (2017)
+            const a1 = 6.5;
+            const a2 = 2.5;
+            const ks = this.prms.Ks.v;
+            return 2 / Math.pow(a1 * a2 * ((Y + ks) / ks) / Math.sqrt(a1 * a1 + a2 * a2 * Math.pow((Y + ks) / ks, 5 / 3)), 2)
         }
     }