Uvas Creek flows east through this canyon from the crest of the Santa Cruz Mountains into an intermontane valley. Being located in a publicly owned mountain park, it will be protected into the foreseeable future.

Man's impact on the riparian (creeks, rivers, etc.) environment is frequently less benign. On nearby ranches, unfettered cattle wander into streams devastating the riparian vegetation and turning clear water into muddy torrents after winter rains. In more urban areas, streams are squeezed into pipes or channeled into concrete troughs to maximize developable land. The result is a barren natural environment and an arid urban landscape.

Human impacts on the riparian environment are discussed below. Proposed for rejection in the future are certain current practices. Proposed to be embraced are alternative approaches for maximizing the potential for ecological diversity and urban delight.

Cows & Fields

To maximize the productive resources of land, many farmers and ranchers make changes to the streamside landscape which can have unintended consequences detrimental to the environment and themselves. These changes to riparian corridors can be as extensive as filling and straightening natural stream beds and their replacement with artificial channels devoid of natural vegetation. They can be as innocent as allowing cattle to freely graze along stream banks. The irony is that a change supposedly to maximize production can in the long run eat away at those natural resources underpinning productive capacity.

The loss of the riparian vegetation by the trampling of hooves or the conscious acts of man removes a key protection against soil erosion. The loss also eliminates a crucial hiding place for wildlife seeking refuge and a corridor to other natural places. Fish dependent on the cooling effect of the shade provided by streamside trees disappear. Floods become more destructive with the loss of the meanders and broad stream beds that slowed and held waters for percolation into the soil. Water tables drop precipitously as a primary water source now races downstream.

Other choices are available. Cattle access to water can be limited to certain controlled places. Streamsides can be fenced to prevent the influx of livestock seeking water or tender green shoots. Protected riparian zones can be created where trees will not be cut and soils will not be graded.

Pipes & Concrete Troughs

One of the most destructive approaches to free flowing streams occurs frequently in cities; the excavation of a stream bed and its replacement with a pipe in which the waters will flow beneath the city growing above. All trace of the stream is gone. The trees, bushes and wildlife once sustained by flowing water can no longer provide a natural relief to the manmade urban environment.

In less densely developed parts of the city, another method has been utilized for controlling the natural riparian flow. Dig a straight and deep channel and line it with concrete. If built large enough to contain the biggest floods, such a channel will prevent water flow into the bordering urban development.

Parents don't encourage their kids to play in the creek flowing along the bottom of the concrete channel shown to the left. With the fast flow and slippery banks, floods become downright dangerous. Catching fish or skipping stones in these waters divested of shade and heated by the adjoining concrete is an exercise in futility. Since flood waters are racing down this trough and have no place to slow down or percolate into the soil, downstream residents face an even greater flood threat.

Either beggar your neighbor or put all the creeks and rivers in these concrete troughs. There has to be another choice.

Protected Riparian Corridors



The left top image shows the intake, where only flood levels above the wall will enter the bypass tunnel. The right top image shows the bypass outflow portion. The lower image presents the resultant urban riparian corridor where new trees have begun to take root.

The most obvious approach is to do it right in the first place, as illustrated in the first image at the top of this page. When exploiting natural resources or developing land along streams, protect an adequate riparian corridor where the natural environment will be preserved or restored - in the case of redevelopment of previously urbanized lands. In order to assure equal impact and opportunity for all riparian landowners, such preservation or restoration will need to be required by the approving governmental body. Otherwise, certain landowners will opt for exploitation or development up to or beyond the stream bank, leaving future flooding costs for subsequent landowners, neighboring residents and the broader community.

Flood Diversion Tunnels

In densely urbanized areas, the cost of restoring previously developed riparian flood plains can be prohibitive. An alternative is to divert floods above a determined volume into a channel created beneath city streets or other public lands. The restored riparian zone can then be narrower, since it will only need to contain sufficient capacity for flood waters within the determined volume.

The Guadalupe River Park Plan (GRPP) shows in yellow the underground bypass channel adjoining the river in San Jose, California.

Although not fully natural riparian landscape, the created environment shown to the right is a decided improvement over the much larger concrete channel originally here proposed for flood control purposes.

Natural Overflow

The bypass channel winds within a reconstructed floodway planted with native trees and other riparian vegetation. The original river channel still flows within the tree canopy to the left in the photo. San Jose's downtown is visible on the horizon.

Bypass channels do not have to be underground. The bypass channel shown below is the lowest point in a floodway. This floodway would contain the flow of the biggest flood associated with this reach of the river. The former homes located here were removed due to the airplane noise level, a floodway was excavated and a natural riparian corridor was created on the west side of the river.

When flood waters rise above a certain volume in the old river channel, the excess will be diverted to the bypass channel running through the replanted riparian landscape. Floods fill the channel and rise within the floodway. The riparian vegetation thrives within periodic flood conditions. The east bank of the river was untouched and floods that periodically overtopped that bank were hopefully no more.

The bypass channel shown in the GRPP was located on land purchased within an airport noise zone. The dark blue indicates the original river channel. The blue green shows the location of the bypass channel cutting through the lowest point in the floodway.

Underground Reservoirs

A percolation pond is a pond that allows water to percolate (or seep) through layers of rock and gravel. The water is cleaned as it slowly travels downward and eventually reaches an underground aquifer. The purpose of these percolation ponds is both to clean the water and to keep the ground from sinking. Ground sinking can occur as water is drawn from, but not replaced, in the aquifer. The resultant underground reservoir is also unaffected by evaporation.

The ponds can be dedicated solely to water percolation with banks barren of all vegetation. Alternatively, these ponds molded by the hand of man can become a vessel for the creation of an expanded natural environment. The latter approach benefits both the urban water supply and the expansion of wildlands within urban reaches.



The upper image shows two percolation ponds in a parklike setting separated by a berm. On the lower left, beside a nearby percolation pond in a more natural landscape, a snowy egret awaits the passing of dinner. The image to the lower right shows the valves used to bring water into the ponds to replace that which has percolated down into the aquifer.