**5. Conclusions**

The main problem with the construction of the dam on the San Pedro-Mezquital river would be the effect of a controlled flow that reaches the wetlands of the alluvial plains, affecting the estuarine and coastal ecology. However, it was observed that the behavior of the flood is the same; thus, the PHLC project does not change the flood conditions of the plain.

Also, the fine material will not represent any continuity problem and will only travel downstream, with a somewhat different distribution in time than what currently occurs, but it will be able to reach the mangrove area without any problem. Opposite to the coarse material that will effectively be retained in the reservoir and, specifically, at the reservoir entrance 60 km from the curtain. However, the amounts of sediment that are calculated in the range from 1.0 to 0.1 mm are of the order of 100,000 m3 per year on average and this is only a small part of all the sediment that will be stored at the reservoir entrance.

Finally, an ecological cost should be assessed considering the contributions of the base flow (underground) since this can substantially alter the ecosystem. Especially, during the dry season, when it would be a higher discharge for these ecosystems. However, the ecosystems from these regions have already evolved to adapt to the dry season, which is necessary for their survival. Thus, the most probable loss of these marshlands is associated mainly with human activities rather than the hydrological behavior of the system.
