docs: add reference for Cemagref equations

Refs #512

docs/en/calculators/structures/cem_88_d.md

@@ -55,7 +55,7 @@ $$Q = \mu' L \sqrt{2g} (h_1-h_2)^{1/2} \left[ h_2 - (h_2 - W) \right] \Rightarro
 
 Classical formulation of submerged orifices, with \(\mu' = \mu_S\).
 
-Orifice weir operation is represented by the equations above and Figure 19. Regardless of the type of flow under load, an equivalent free flow coefficient is calculated corresponding to the conventional free orifice formulation:
+Orifice weir operation is represented by the equations above and Figure below. Regardless of the type of flow under load, an equivalent free flow coefficient is calculated corresponding to the conventional free orifice formulation:
 
 \(C_F = \frac{Q}{L \sqrt{2g} W (h_1 - 0.5 W)^{1/2}}\)
 
@@ -67,4 +67,6 @@ Orifice weir operation is represented by the equations above and Figure 19. Rega
  * (16) : Orifice - totally submerged
  * (14) : Orifice - free flow
 
-Figure 19. Weir - Orifice
+## References
+
+Baume, Jean-Pierre. 1988. « Modélisation des ouvrages de type : déversoir, vanne, orifice, dans les modèles d’hydraulique à surface libre ». Montpellier n°205-Document de travail 87.1. Montpellier, France: CEMAGREF. [https://hal.inrae.fr/hal-04970129](https://hal.inrae.fr/hal-04970129)

docs/en/calculators/structures/cem_88_v.md

@@ -62,7 +62,7 @@ with : \(\alpha_1 = 1 - 0.14 \frac{h_2 - W}{W}\)
 
 \((\alpha_1 = \alpha (h_2-W))\)
 
-Weir gate operation is represented by the above equations and Figure 20. Regardless of the type of flow under load, an equivalent free flow coefficient is calculated corresponding to a conventional free flow gate design:
+Weir gate operation is represented by the above equations and Figure below. Regardless of the type of flow under load, an equivalent free flow coefficient is calculated corresponding to a conventional free flow gate design:
 
 \(C_F = \frac{Q}{L\sqrt{2g} W \sqrt{h_1}}\)
 
@@ -78,4 +78,6 @@ Note: it is possible to obtain \(C_F \neq C_G\), even under free flow conditions
  * (20) : Orifice - totally submerged
  * (18) : Orifice - free flow
 
-Figure 20. Weir - orifice
+## References
+
+Baume, Jean-Pierre. 1988. « Modélisation des ouvrages de type : déversoir, vanne, orifice, dans les modèles d’hydraulique à surface libre ». Montpellier n°205-Document de travail 87.1. Montpellier, France: CEMAGREF. [https://hal.inrae.fr/hal-04970129](https://hal.inrae.fr/hal-04970129)