Streambank erosion is a huge problem for the health of streams in the United States and around the world. Some effects of streambank erosion on streams are the increase of suspended and settled sediment in the stream and extreme change of physical characteristics of stream causing decrease in baseload flow, change in meander and change in water depth. These changes have many negative effects on the aquatic life in the streams. Sedimentation of streams causes an increase in turbidity and a decrease in disolved oxygen. Sedimentation can also fill up interstitial spaces which small fish and invertebrates use for their survival.
It is proven that impervious surfaces have contributed to the huge increase in stormwater runoff. This increase in runoff has overwhelmed the carrying capacity of the streams and has caused the streams to flow with a velocity which causes scouring of the streambanks. The vegetal riparian buffers would have been able to lessen the effects of the stormwater surge on the stream. However most streams no longer have vegetal buffers or have had their buffers greatly reduced.
Another cause for streambank erosion is the practice of farmers allowing catle to wade in streams to cool down and drink water. Cattle destroy the vegetal buffer and greatly reduce streambank stability by trodding in and out of the streams, physically cleving off the streambank little by little.
It is proven that impervious surfaces have contributed to the huge increase in stormwater runoff. This increase in runoff has overwhelmed the carrying capacity of the streams and has caused the streams to flow with a velocity which causes scouring of the streambanks. The vegetal riparian buffers would have been able to lessen the effects of the stormwater surge on the stream. However most streams no longer have vegetal buffers or have had their buffers greatly reduced.
Another cause for streambank erosion is the practice of farmers allowing catle to wade in streams to cool down and drink water. Cattle destroy the vegetal buffer and greatly reduce streambank stability by trodding in and out of the streams, physically cleving off the streambank little by little.
These farming practices are being addressed by the US department of Agriculture (USDA). Through the USDA Farm Bill, Funding and tax credits are made available for farmers to use Best Management Practices (BMPs). This funding has greatly influenced farmers to use these BMPs and thus has been a method for rebuilding vegetal riparian buffers and stopping stream degradation by cattle and other livestock.
Urbanization has had huge negative impacts on stream water quality as it has been the major impetus for many activities causing stream degradation. The development of rural land has caused an increase in the land value surrounding the new development which cause economic pressures on the farms in those areas as they are required to pay the increase on their real estate property tax. Thus the farms respond by putting more cattle on their land to pay for the increase in the taxes. This has resulted in an increase in cows wading in the streams which has then caused an increase in streambank degradation.
Below is a diagram I constructed using Vensim PLE showing the many various factors associated with streambank degradation.
In order to understand the evolution of the problem I would need track change in stream depth and stream width. I would also need to know the change in the amount of Estimate Impervious Surfaces (EIS) over time. I would need data on the changes in property values through time. I would need to know to what extent rural land has been developed. These are the "hard" elements in the system.
The "soft" elements, ones which are not easily quantifiable, in this system are farming practices, social impact of policy changes on farmers, social and economic impact of development of rural land on farmers, and the rate of utilization of livestock fattening BMPs.
Good choice of topic Megan. The same problem exists here in Malta to a certain extent; main cause being urbanisation. The causal loop diagram portrays in a very good simplified manner what is actually happening in this degrading process. I would also have added the following variables to your diagram; influence on flora and fauna, and flooding (caused by excessive amounts of sedimentation blocking stream flow).What could have been even more interesting was developing the diagram in such a way to draw up any possible feedback loops.
ReplyDelete