The Hahamongna Watershed Park is undergoing a public review as a result of the public outcry against the devastation of the Arcadia Woodlands and the discovery of the LA County plans to move massive amounts of sediment into the park, which provides for the natural drainage of the Arroyo Seco. Hahamongna is a precious natural resource, not a sediment dump, as chief citizen defender Mary Barrie has documented extensively in public hearing. This has forced the County into an EIR process to show the public what it intends to do in response to the sediment piling up behind Devil's Gate Dam, as a result of lack of maintenance as well as a consequence of the Station Fire. The announcement for the scoping meetings by the County is here on their website.
Karen Bugge, the Altadena Hiker, has posted her story for the EIR process here. I have also participated in the scoping meeting, and submitted the following recommendation for management of this watershed in a new era that is "post-hydraulic" in terms of dealing with nature's processes and the consequences of treating natural water systems like a plumbing project:
Dam reconstruction is effective and entirely feasible in the restoration of natural processes which carry away the sediment instead of trucking it from behind an outdated and unmaintained dam. The short-term costs to change the dam structure and clear out the obstructions to natural flow are vastly smaller than ongoing sediment removal programs which are not actually carried out, for cost reasons, endangering all the communities downstream of the dam. Life cycle estimates (100 years) should be the basis for cost comparisons that include the maintenance and repair for all structures, and this would integrate the value of natural ecosystems into the equation.
Sediment management is the self-inflicted result of placing dams in the way of natural water processes that carry the sediment to the base of the mountains and create a fertile alluvial plain. In order to replenish nutrients in the soil, as well as recharge the natural aquifers that supply well water, these natural drainage patterns must be restored. That doesn't preclude artificial water storage, but these strategies must engage the natural terrain properties that exist free of charge. Water flow moves sediment, and managing that flow rather than stopping it provides a sustainable way to provide water, soil nutrients, sand, gravel and mud into areas that sustain the ecology of the region.
Natural flood protection can be attained by protecting and restoring wetlands and floodplains, and by restoring a river’s natural flow and meandering channel. Giving at least some floodplain back to a river will give the river more room to spread out. Furthermore, wetlands act as natural sponges, storing and slowly releasing floodwaters after peak flood flows have passed.
The following steps should be taken:
1. Adopt a strategic conceptual plan identifying the watershed region and its component functioning parts. Begin implementation of this concept by adopting public-private partnerships that can continually fund the ongoing restoration efforts through private fiscal investment repaid with bond or tax structures. Partner with communities and their leadership, mountains conservancies, conservation nonprofits and the County. Everyone working together can make this happen.
2. Implement reconstruction/modification of the dam to allow water and sediment flows downstream into the areas that need these natural flows. Develop water storage strategies that are effective and multivalent, possibly a series of check dams that work in optimal natural locations and recharge the Raymond Aquifer.
3. Establish a flood plain easement program to minimize flood impacts, reduce repeat damages and store floodwaters for benefits of downstream residents and communities.