Ask Mr. Smarty Plants

The purported high ground water usage by Juniperus ashei (Ashe juniper) has earned it the name "water hog", but there is evidence to the contrary and a growing number of people now believe that this is not strictly the case.  Below are several articles that address this assumption about Texas cedar.

This article, Holistic perspective on juniper by Steve Nelle from the Texas Natural Resources Server, is focused on range/pasture management, not river banks but it does have some interesting points to make that would be applicable to your question.

Here is a quote from this article:

"Much of the current emphasis on juniper control revolves around its role in the water cycle. Thick stands of juniper intercept large amounts of rainfall and utilize considerable soil moisture which decreases deep percolation, springflow and aquifer recharge. However, the removal of juniper does not automatically improve these watershed dynamics and could in fact make them worse.

If juniper control is followed by long term judicious management which promotes a good grass response, then watershed functions (runoff quality and subsurface quantity) should improve. However, a good cover of mid grasses also intercepts rainfall and utilizes soil moisture, so the net gain in aquifer recharge may be negligible.

If juniper control is not followed by proper grazing management, a good grass cover will not develop. Runoff will increase and deep percolation will be minimal. Much past juniper control has resulted in massive soil erosion (Marsh and Marsh 1992). A dense cover of juniper is better watershed protection than a poor cover of grass."

"Brush Management" by Gregg Eckhardt on the Edwards Aquifer Website cites studies by James Heilman of Texas A&M that concludes that oaks use more water than cedars and that a brush cover (with cedars included) uses only slightly more water than grass coverage.

Biology and ecology of Ashe juniper by F. E. Smeins and S. D. Fuhlendorf from the Texas Natural Resources Server talks about the ecology and biology of the Texas cedar and offers some pros and cons about leaving them or removing them.

Pros of leaving Texas cedars in place: 

• Can help prevent erosion on steep sites where they are already established
• Bark of mature cedars are used by the endangered golden-cheeked warbler (Dendroica chrysoparia) for nest building
• Provide shelter and food for wildife

Cons of leaving Texas cedars in place:

• Concerns that they are consuming large amounts of water that could be used by more desirable plants
• Cedars may out-compete other species for space and essentially become a monoculture
• Male trees produce pollen that is a severe allergen for some people

You will have to weigh the pros and cons to make your decision but I think there would be merit to leaving well-established trees with roots that are holding the soil in place.  If they are beginning to form a monoculture you might consider thinning them out, but be aware that removing a large number of them could result in erosion.

For the second part of your question, here are some suggestions for plants along the river banks.  I am not sure what county (perhaps Bastrop County since that is where Rosanky is) along the Blanco River you are concerned about, but the plants listed below are known to grow in at most of the counties along its route to the Gulf of Mexico:

SHRUBS/SMALL TREES

Cephalanthus occidentalis (Common buttonbush)

Amorpha fruticosa (Indigo bush)

Ilex decidua (Possumhaw)

Ilex vomitoria (Yaupon)

Malvaviscus arboreus var. drummondii (Turk's cap or turkscap)

Callicarpa americana (American beautyberry)

GRASSES–grasses have fibrous roots that are very good at holding soil

Andropogon glomeratus (Bushy bluestem)

Chasmanthium latifolium (Inland sea oats)

Panicum virgatum (Switchgrass)

Sorghastrum nutans (Indiangrass)

Tripsacum dactyloides (Eastern gamagrass)