Section 5 – Sediment, Erosion and Soils

 

"Human vanity can best be served by the reminder that

Whatever his accomplishments

His sophistication

His artistic pretension,

Man owes his very existence to a six inch layer of topsoil

And the fact that it rains”

 

Author, Unknown

 

“The Nation that destroys its soils, destroys itself”

 

F. D. Roosevelt, President of the United States

 

Introduction

This section of the watershed assessment focuses on hydrological and geological processes and their influences upon a watershed.  These processes whether natural or due to man-made influences can cause impacts to the watershed as erosion of soils and other materials – and effect water quality.  Loss of fertile soils, vegetation, impacts to habitat as well as significant scarring and unintended alteration of watershed lands can occur.  This section of the assessment is an initial effort to understand what impacts to soils and the watershed landscape could have been affected by significant alterations caused by erosion.

Soil Type and Structure

The Natural Resources Conservation Service has extensive Soil Surveys for both Fresno and Madera County.  According to the Madera Soil Survey, soil is a natural body on the surface of the earth composed of organic and mineral materials.  Soils include biological forces – the plant and animal life in and on the soil.[1]  Soil structure can affect the way in which water percolates into the ground and is retained – or how it behaves as surface run-off.

This watershed assessment developed a significant interest in the organic aspect of soil composition.  Much discussion has focused on the organic or soil biota and the presence of micro-organisms as being the key indices for determining the health of the soil – and the role of a “healthy” soil as a diverse living environment.  This includes denoting a close association between beneficial fungi (myco) and plant roots (rhiza).[2]  The Natural Resources Conservation Service has a number of soil quality information related to rangeland health indicators.[3]  Soil health and its effect on surface water collection, percolation and retention is also a strong area of interest.[4]  The effect of thin non-biotic soil structures as conducive to weed species is also an area that generates great interest. There is a strong belief among a number of individuals of the important role that soil plays in a supporting a biologically diverse and healthy watershed ecosystem.

Within the Millerton watershed area there are five major soil associations.[5]  According to the Todd Engineer Technical Memorandum, these soil types can vary from a very few inches to up to six feet in depth.  The following are the major soil associations and their characteristics:

 

Daulton-Whiterock Association. These soils occur in a five-mile wide discontinuous band along the lower foothills between elevations 500 and 1,000 feet MSL. The soils are developed on slate and schist in hilly topography with slopes varying widely from 8 to 45 percent. Both soils are notable for rock outcrops known as “graveyard” or “tombstone” schist. The Daulton soils are relatively extensive (about 30,300 acres), while the Whiterock soils are very limited in extent (664 acres). The Daulton and Whiterock soils are relatively coarse (loam, fine sandy loam, rocky fine sandy loam) with moderate to rapid infiltration. However, the soils are thin with low water holding capacity, which limits the opportunity for retention of rainfall and subsequent percolation to the water table. The representative profile for the Daulton soil is only 17 inches thick, while that of the Whiterock soil is only 8 inches.

 

Ahwahnee-Vista Association. The Ahwahnee-Vista Association dominates the foothills, accounting for nearly 192,800 acres over a 10- to 15-mile wide band between 500 and 1,500 feet MSL. Both the Ahwahnee and Vista soils are developed on decomposing granite. The Ahwahnee soils are mapped together with Auberry and Vista soils. The Ahwahnee and Vista soils occur on a wide range of slopes varying from 8 to 75 percent. The Ahwahnee soils generally are deep (48 to 60 inches) with thinner profiles occurring on the steeper slopes. The soils range in texture from coarse sandy loams to very rocky coarse sandy loams on steeper slopes, where the soils are marked by extensive bedrock outcrops. Given the coarse texture of the Ahwahnee soils, they are likely permeable. The thicker profiles also provide moderate water holding capacity, providing temporary storage and thereby increasing the potential for water to percolate downward toward the water table.

The closely associated Vista soils generally occur in the lower foothills and on relatively gentle (3 to 8 percent) slopes. The Vista soils are coarse textured (coarse sandy loam), but thinner than the Ahwahnee soils with depth to bedrock of about 36 inches. The Vista soils also are relatively permeable and have moderate water holding capacity.

 

Ahwahnee-Auberry Association. This association (covering nearly 52,500 acres) occurs on the higher foothills in a discontinuous band between elevations 1,500 and 2,800 feet MSL. The Ahwahnee and Auberry soils occur on a wide range of slopes (8 to 75 percent).  As described for the Ahwahnee-Vista Association, the Ahwahnee soils generally are deep, except on steeper slopes, and consist of coarse sandy loams to very rocky coarse sandy loams. Given their coarse texture and relatively thick profile, Ahwahnee soils are relatively significant to groundwater recharge in upland areas. The Auberry and Ahwahnee soils are similar, but the Auberry soils have finer-textured subsoils. While the representative Ahwahnee soil is a coarse sandy loam throughout the profile, the representative Auberry soil consists of a surficial sandy loam overlying with lower zones including sandy loam, gritty loam, sandy clay loam, and sandy loam zones. Accordingly, while internal drainage in the Ahwahnee soil is rapid, that of the Auberry soil is medium to moderately slow.

 

Coarsegold-Trabuco Association. This soil association occurs in the foothills between elevations 1,500 and 3,500 feet MSL, similar to but slightly higher than the Ahwahnee-Auberry Association. The Coarsegold-Trabuco Association includes reddish soils developed on metasedimentary and intrusive igneous rocks. The Coarsegold soils predominate in the association (about 37,300 acres) and occur on rolling topography with 8 to 75 percent slopes and rock outcrops on the steeper slopes. The Coarsegold soils include loams and rocky loams on the steeper slopes. The loam soils generally are more than 34 inches thick, with the representative profile including a surficial loam and subsoil clay loam to a depth of 38 inches over disintegrating schist bedrock. The soil has moderate water holding capacity, but internal drainage is moderately slow, given the relatively fine-textured subsoil zones.

The geographically-limited Trabuco soils (2,320 acres) consist of rocky loam and loam soils with depths ranging from a few inches to more than six feet. The representative profile of the Trabuco rocky loam includes surficial loam over gravelly clay loam and a hard clay subsoil. As a result, these soils have slow internal drainage.

 

Holland-Tollhouse Association. The Holland-Tollhouse soils occur between elevations 2,800 and 3,500 feet MSL and have developed on coarse-grained granitic bedrock. The more extensive Holland soils (about 18,000 acres) occur in the high foothills with slopes ranging from 15 to 45 percent. These soils are sandy loams and rocky sandy loams with sandy clay loam subsoil. The soils are relatively deep; the representative profile for the Holland sandy loam extends downward to disintegrating granite at 58 inches. The Holland soils have moderate soil water holding capacity, but moderately slow internal drainage.

The Tollhouse soils occur over about 3,300 acres in the lower mountains. These soils occur on steep slopes (30 to 75 percent), are relatively thin (3 to 36 inches to bedrock), and marked by bedrock outcrops. The soils are rocky coarse sandy loams characterized by very rapid runoff and rapid internal drainage. These characteristics limit the significance of the Tollhouse soils with regard to recharge of groundwater.

Erosion – Natural Influences

Very little if any existing data was obtained regarding the general type or extent of erosion that may be occurring within the watershed study area due to natural influences.  Predictive models were reviewed that may be useful to obtain a general estimate of sediment being produced.  The Water Erosion Prediction Project (WEPP) model is one such tool for estimating soil loss and sediment yield.  This model was developed by the National Soil Erosion Research Laboratory (NSERL)[6] of the USDA and is located at Purdue University.  An effort was made to review the underlying logic of this model – and to ascertain what a possible sediment yield may generally be within the Millerton watershed.  Input variables included using Auberry as the soil type, precipitation data from the Friant Government Camp and wheatgrass-needlegrass as the common vegetation with grazing.  The model yielded a soil loss/sediment yield of .6 of a ton per acre per year.  This could be representative of a significant amount of general erosion – however, this would require further investigation.  Additionally, the San Joaquin Experimental Range may have historic research data that could be obtained for further investigation.

Erosion – Land Use and Infrastructural Effects

Again, very little information was obtained regarding the type or extent of soil erosion that may be occurring within the watershed study area due to land use and infrastructural effects.  Sedimentation models tools such as a part of the California Department of Forestry’s Fire and Resource Assessment Program (FRAP) include SEDMOL, a road sedimentation model as a way in which to possibly predict as a first level estimate the amount of erosion that may be contributed from unpaved road systems.  The most recent sediment predicting model is SEDMODL2 available from the National Council for Air and Stream Improvement, Inc.   A common source of erosion and thus sediment is what is commonly called a “shotgun” culvert.  These culverts may have been placed improperly – constricting the natural flow regime of natural drainages.  Extensive cut and fills from grading activities for roads and developments could also be contributing factors of erosion.  How roads are designed, constructed and maintained in range and forest lands can be a contributing factor as well.[7]

 

Summary of Findings

 

1.      Natural occurrences or man made influences that create erosion and the production of sediment can affect water quality and impair a watershed in many ways – and this in turn relates to the percent of ground water recharge in fractured rock formations.

 

2.      Historically, Extensive field investigations conducted by the US Soils Conservation Service (now Natural Resources Conservation Service or NRCS) have resulted in a comprehensive cataloging and analysis of soil associations within the Millerton watershed.

 

3.      There are five major soil associations within the Millerton watershed.  The dominate soil is the Ahwahnee-Vista Association followed by the Ahwahnee-Auberry Association.

 

4.      Soil structure and its composition can affect the way in which water percolates into the ground and is retained – and relates to the percent of ground water recharge capability even within fractured rock formations.

 

5.      Soils include a biotic component that has been recognized by the NRCS – if not fully investigated.

 

6.      This biotic component and the investigation of micro-organisms as indices for determining the health of soil has not been a conventional area of focus – or for the determination of a watershed’s condition.

 

7.      There appeared not to be any investigations that have occurred relative to soils composition and structure – and the effect on surface water collection, percolation and retention within the watershed.

 

8.      There appeared not to be any investigations that have occurred relative to soils composition and structure – and the effect on vegetation - or in respect to native versus non-native species – or the proliferation of noxious weed species within the watershed.

 

9.      There appeared not to be any investigations that have occurred relative to soils composition and structure – and an association with the diversity of flora and fauna within the watershed.

 

10.  There are simulation models available that may assist in determining sediment production in the watershed and its criticality in respect to detrimental aspects of erosion – or to water quality within the watershed.

 

11.  There appears to be very little information regarding erosion within the watershed regarding the natural or man-made contributions – and the criticality of the occurrences.

 

12.  There appears to be very little information regarding soils in relation to climate.

 

13.  There appears to be very little information regarding soils in relation to carbon sequestration.

 

Conclusions

 

1.      Soil associations and locations may be known for the watershed.  However, there are no known field studies that have been conducted within the Millerton area watershed to determine what role surface soils, their composition and condition may contribute towards moisture collection, retention, percolation and ground water quantity.

 

2.      There are no known field studies that have been conducted within the Millerton area watershed to determine what role surface soils, their composition and condition may contribute towards surface and ground water quality.

 

3.      There are no known field studies that been conducted within the Millerton area watershed to determine what role surface soil compositions and conditions contribute to the diversity of flora and fauna – and the overall productivity of the landscape.

 

4.      There are no known field studies that have been conducted within the Millerton area watershed to determine what role that surface soil composition and conditions contribute to vegetation – and in respect to native versus non-native species – or the proliferation of noxious weed species.

 

5.      Soil quality may have a strong link to carbon sequestering, ground water recharge capabilities and overall landscape productivity that could be beneficial to the overall health of the Millerton area watershed.