Power of a Rain drop

interaction of water with soil 2/3rds of the riparian story Vegetation

Dissipation of energy of accumulated raindrops (deposition and erosion)

Meander is an energy dissipation strategy Meandering of Gulf Stream in Atlantic

Rivers will be crooked Walla Walla River, 1964

Lesson 1 creeks will meander Creeks do not want to be wide and straight

Meander and gradient Hill Hill Hill Hill Elev 1500 Channel Length 25,000 ft Gradient 0.4% Gradient 1.0% Channel Length 14,000 ft Gradient 0.7% Hill Hill Valley Length: 10,000 ft Elev - 1600

Channels design themselves to manage the energy/water and sediment delivered them in most efficient manner

Floodplains Dissipate Energy and Trap Sediment (#) Floodplains Dissipate Energy and Trap Sediment Above Bank full is Floodflow Everything above is active floodplain. (Active, not 100 yr.) During Flood flow a high energy moves the sediment through the system, but low energy in the floodplain to capture some of the sediment. Really two columns of water at work. Flood plain is a pressure relief valve of the channel Low velocity water Active Floodplain High velocity water

Floodplain

Flooding Recharges Water Tables (#) Flooding Recharges Water Tables Important to note that the water table and the water in the creek is the SAME WATER. At base flow the water table is contributing to the creek. In flood flow the creek is contributing to the water table. Water Table

Excessive Energy (Erosion) Enlarges the Channel (#) Excessive Energy (Erosion) Enlarges the Channel Here is the channel that has designed itself over time to drain the landscape, carry appropriate volume and velocity of flood waters and move the sediment produced within that system. More runoff than the system was designed to handle and or vegetation component has been impaired. This is what can happen when energy of floodwater exceeds the strength of poorly vegetated banks.

Lane’s Relationship, 1950 without vegetation

Enlarged channel

Down-cutting Drains the Water Table (#) Down-cutting Drains the Water Table Downcutting reduces the water table and bank storage, amounts to drying out the riparian system. There is a permanent loss of the water table when down cutting occurs.

Down-cutting: Loose Access to Floodplain (#) Down-cutting: Loose Access to Floodplain Bankfull flow well below floodplain Original channel at bank full That same volume of water that used to access the floodplain no longer gets out It has no way to dissipate its energy, so all that energy is banging against the sides and bottom of the channel.

Loss of floodplain

Where does flow come from during dry times? (#) Where does flow come from during dry times? Water Table Riparian Sponge Rock Layer Creeks in the headwater region operate in a similar fashion even though they are confined by a rock layer. Headwater Stream

The Water Table Sustains Base Flow (#) The Water Table Sustains Base Flow Maintenance of base flow is especially dependent on the water table

Riparian Sponge

Channel Widening Reduces the Riparian Sponge (#) Channel Widening Reduces the Riparian Sponge Process of channel erosion (caused by inadequate vegetation) is different in rock bottom channels. Loss of water storage. HOW MUCH RIPARIAN SPONGE HAS BEEN LOST/ all that left is this tiny little sponge.

Loss of sponge in headwater streams means reduced base flows

Overly Wide Channels Reduce Sediment Transport Ability (#) Overly Wide Channels Reduce Sediment Transport Ability Still a base flow (only a few inches deep) and still a bankfull flow, but no bona fide channel where the energy is high enough to transport sediment. This is why many headwater creeks have massive gravel deposits that accumulate and move from place to place and never seem to get stabilized. The channel cannot decide where it wants to be.

Sediment can not be efficiently transport

Degraded and eroded channels can be restored (#) Degraded and eroded channels can be restored The good news is that both channel types can repair themselves according to the natural processes of channel restoration The essential thing is the presence of at least some stabilizing vegetation to start the process. Channel Flood Plain Water table All at a reduced elevation Natural Channel Restoration

Dissipating Energy and Catching Sediment (#) Dissipating Energy and Catching Sediment

Function will return at a new elevation. (#) Function will return at a new elevation.

Early Signs that recover is occurring

(#)

Recovery can start with one plant.

Sponge can be built by the creek on top of bedrock

Recovery occurs without intervention once hindrances are removed 2007 06 PFC Erosion/Deposition Items 1_18_2008 Recovery occurs without intervention once hindrances are removed 2008 Nueces River 2011 2010 32

(#) Burro Creek 1981 Burro Creek 2000

With new understanding you can see what is missing

Recovery Potential for pastures is widely accepted and understood

Why not riparian recovery?

Starts energy dissipation usually a plant