3.3.2. The SRMF Hydraulic System

The water system's ability to harness the Eresma River flow, in order to convey the hydraulic energy required to power the equipment related to mechanical and auxiliary processes, was key to the successful operation of the SRMF. The goal of Juan de Herrera's water system design was to adapt the existing structure, which had served the old San Millan Mill, to the more demanding requirements of the SRMF.

The original gravity dam, with an arched floor and lateral drainage located in the left abutment, manually regulated by two gates, was modified to incorporate an outlet meant to divert enough of the Eresma River flow to actuate the waterwheels placed along the façade of the Ingenio Grande (see Figures 9 and 10). The surplus capacity of the bypass channel was designed to be poured by coronation (see Figures 11 and 12). This system was intended to reduce the number of waterwheels used, in case of a decrease in flow availability caused by intense drought [13].

**Figure 9.** Forging shop waterwheels and the channels. (Image property of the authors).

**Figure 10.** Forge blower waterwheel. (Image property of the authors).

**Figure 11.** (Image property of the authors).

**Figure 12.** Entrance of the water flow in the SRMF. The right opening connects to the channel that feeds the waterwheels, while the left one returns the surplus water to the Eresma River. (Image property of the authors).
