A Brief History of Lower Walnut Creek

Overview
Lower Walnut Creek today looks significantly different than when it was channelized over 60 years ago. Even back in 1963, when the Corps began its efforts in the watershed, Lower Walnut Creek was far from pristine and untouched.

Development
When farms and fields are developed into commercial, residential, and industrial uses, areas where water used to drain into the soil became paved over. This new impervious surface meant that less water soaked into the ground and more ran off into creeks. Natural processes had formed the creeks to a certain size, and this additional runoff meant the creeks flooded more often.

To make matters worse, some of the most desirable flat lands for farming and development were near the creek in its historic floodplain. The high value of this land set up tremendous pressures to reduce flood damages and tame the creek.

Channelization
Historic aerial photos from 1939 show the alignment of Walnut Creek to be significantly different from when the Corps began work in 1963. In the 1940s and 1950s, the natural creek was channelized by neighboring landowners to help keep stormwater in the creek and to pass it through the system efficiently. When the Corps was asked to help the situation in the 1960s, the resulting project further widened the already channelized creek and constructed levees to allow the water to rise higher without escaping.

The newly-formed Flood Control District (District) was the non-federal sponsor for this work by the Corps of Engineers and signed agreements saying they would own and maintain the channel in perpetuity. Calculations at the time showed the channel would need minimal maintenance, and sufficient funds were available to perform this maintenance.

Sediment

Soon after Lower Walnut Creek was handed over to the Flood Control District for maintenance, it became clear that much more sediment was depositing in the creek than was originally calculated by the Corps. The Corps returned in 1973 and participated in dredging the lower channel, removing over 850,000 cubic yards of sand and mud.

When the District prepared to dredge the channel again in the early 1990s, it because clear that significant habitat for wildlife had formed in the channel since the last invasive dredge and getting regulatory permits necessary to do this work would prove difficult and enormously costly. This difficulty was compounded by the reduction in the district’s property tax funds as a result of the passage of Prop 13 in 1978.

Unfortunately, leaving the habitat in place was not an acceptable maintenance practice in the eyes of the Corps of Engineers. This conflict put the District in a no-win situation:

  1. Should the District remove all the vegetation and habitat in the channel to restore it to its 1960s configuration?
  2. Should the District allow the sediment, vegetation and habitat to remain but be out of conformance with the Corps maintenance requirements?

The District chose a third option, which was to partner with the Corps of Engineers to reevaluate the operation of the channel and transform it into a more sustainable facility. This is the genesis of the Lower Walnut Creek Restoration Project.