Lake Level Report – Boat Dock Survey


A section from the Lake Level Monitoring report contained in Staff Report from the December 13, 2012 board meeting material.  This section drafted by district staff.

LLRpt Fig 18The Devils Lake Water Improvement District conducted a boat dock survey this fall. Water depths were taken at each of the 393 structures on Oregon Department of State Lands list of registered and unregistered docks for Devils Lake. These predominately were located in the jurisdictional waters of the state, although some docks which were measured were outside this boundary in dredged out areas or canals. Depths were recorded at 1 to 2 spots on the dock. The primary depth was taken at the point where the motor of a boat would typically be located if moored at the apparent preferred docking locale. For some docks an optional mooring site was recorded which may provide the upland land owner another position within the existing configuration of the dock to moor their boat. The Crystal Lagoon area was not surveyed, but previous outings confirm this area is utilized and anecdotally favored by non-motorized crafts such as kayaks and canoes. Non jurisdictional docks exist in the back canal system, nor for the most part exist as the width of the canal system largely precludes such structures.

Depth soundings were taken using a fixed device with a 6” square base to standardize the measurements in the variable substrates (muck, sand, bedrock). Depth measurements were recorded in 3” increments which were later converted to decimal feet. Given the nature of taking depths from a boat in real world conditions, the surveyors were conservative in their recording, erring on the low side of a measurement. In other words, the measurements were made in a way that may have slightly underestimated the actual depth of water available by up to 3”. The current lake stage was recorded for each day of sampling, and the depths normalize to water depths of 9.53’ (maximum impoundment), 9.0’ (2012 impoundment), and 8.6’ (anticipated water height after evaporation period for 2012 – this is also near the typical water height seen in the late summer predam modification in 2006).

As to the structures themselves, they vary significantly today and have over time. Intended uses of docks also vary widely as do the vessels individuals utilize to access the water. A review of the various boats known to be typically found on Devils Lake as presented in May 2012, show that draft requirements are in the range of 9” to 22”. Paddle boats and kayaks, not represented by those numbers, are known to need generally less while sailboats, also outside of the original assessment, tend to have an increase depth requirement. Boat docks overtime have been likely built to accommodate one or more of these uses and ranges. However blanket assumption of use(s) is/are not possible. To predict the actual intended use of a dock when it was built would be infeasible. While the appearance of dock may lend itself to one assumed use (mooring a moderate size boat) some owners may have chosen to build their structures for use only as a fishing pier, or other type of use unrelated to boating altogether such as wildlife viewing. At any rate an attempt to estimate the intended use of the 393 structures on the lake has been made.

LLRpt Fig 19Based on Oregon Department of State land Registrations, some intended uses are known. These include marinas, combo boathouses/living areas, and boat houses. However, ultimately it is the property owner (or previous property owners) which make the decision as to the structure’s size and extent based on personal preference, state allowances, moorage needs, and economics. As access to boathouses and combo living areas is limited this survey was unable to accurately determine depths within these structures, they have been only given a cursory review in the analysis. For the purposes of this boat dock survey classification of other structures were made which include Motor boat dock (dock lengths of 30’+), Small boat dock (20’-30’), and Piers (<20’). Data within these classes were available and have a more detailed analysis of  depths. Structures were also separated by whether they were in the state jurisdiction or were nonjurisdictional. Only small boat docks had non-jurisdictional structures and are thus noted. Access from non—jurisdictional structures are limited to the private investment of dredging (or lack there of) that created and maintain the accesses as they were not part of the lake when it was meandered. Classifications were made using estimated dimension values based on aerial photographs and/or observations in the field, therefore while every attempt was made to be accurate in this assessment, the following review should serve as an informational guide only.

As shown in Table 1 all depths are provided in feet based on varying lake elevations of 9.53’, 9.0’ and 8.6’. A second set of data for depths is given for alternate of Optional  docking areas at that same property. These data are also provided in feet with decimals to the hundredths place. The arithmetic mean, median, mode, and standard deviation of each set of data are provided. It should be noted that these summary data are skewed as any depths in excess of 5’ were recorded as 5’ 3” where the actual depths may have exceeded this. As a result mean and median values are represented slightly less than what the field measurements would allow.

Table 1. Dock structure statistics by classification at primary and optional mooring sites. Data are conservative based on the data do not fully represent docks with greater than 5’ of depth, and sample data were rounded down to the next lowest 3” increment for any dock in which the data acquisition was less confidently obtained.LLRpt Fig 20

Table 2 shows the number of structures that are understood through this analysis to have less than 3’ of water under them at three varying water heights, 9.53’, 9.0’, and 8.6’. For example of the total of 393 structures that were assessed, 110 (28%) have less than 3.00’ of water when the lake is at 9.53. Similarly, if the height is 9.0’, that number increases to 171 (44%) and 228 (58%) if the lake reaches 8.6’. Given that as shown in Table 1 the mean depths at 9.53’, 9.0’, and 8.6’ are 3.63’, 3.10, and 2.70 respectively, with standard deviations all of 1.17’, these percentages are sensible. The value of 3’ was used based on what the state uses as a guideline for building new grant funded docks for medium-sized boats as explained later. The 3’ value was extended to the hundredths place for this exercise as mathematically the cut off was made to the hundredths place with no rounding. Properties that had 2.97’ of depth would thus be included in this calculation even though the raw measurements have an error of 3” and the number of significant figures should be limited to two (e.g. 3.0’, not 2.97’). Nonetheless for easy of readability the hundredths places are shown as were the calculation made.

Table 2 continues with categorization of the structures into subgroups of Motor Boat Docks, Small Craft Docks, and piers. In some cases, further classification are shown for jurisdictional and onjurisdictional structures, as well as alternate mooring sites labeled as “Option”. These moorage depths reflect other mooring sites available to the dock users based on the current configuration of the structures. Only Small Craft Boat Docks had non-jurisdictional classifications, and thus are the only one shown as such. Optional mooring sites are more consistent with larger boat docks. Boathouses and combo structures were not assessed to this degree as the capacity to measure these structures accurately was limited. While this boat dock survey was able to fairly accurately determine depth at most of the existing structures, determining any actual impact from an impoundment regime is not possible as “safe moorage” as codified through the county ordinance (See paragraph below) is arbitrary and associated directly to the watercraft to be moored, and not to any official standard. Further the draft requirements of vessels typically seen around Devils Lake range from 9’ to 22”, and thus a while 3’ of depth may be preferred, less than that might be well adequate for the user and private owner of the dock who ultimately have control over the design of the dock structure. For example a number of docks were observed to likely serve only the paddleboat stored on top of the dock as the dock was quite small and did not extend into the lake more than a few feet. These structures are however captured by the following analysis as small craft docks and they too may skew the data if one is assuming that a 3’ depth is what must be achieved to have recreational access.

Table 2. Dock structures by number and percent of total that have depths to the sediment of less than 3′ based on lake levels of 9.53′, 9.0′, and 8.6′. Categorization done as All Structures, Motor Boat Docks, Small Craft Docks, and piers with further analysis shown for jurisdictional waters and optional docking areas where available. Docks with less than 3’ of water does not necessarily preclude recreational access.LLRpt Fig 21LLRpt Fig 22

Table 3 evaluates the number of docks which were likely built post 1992, basically sometime prior to the installation of the dam and whether those docks have depths of water of less than 3’ similar to how Table 2 was calculated. These numbers come from counts from aerial photographs from that time period. Of the 393 structures today, at least 300 were built in some form prior to 1992. Of the remaining 93 structures, 30 were inconclusive but were added to the sub-group of post 1992 to be conservative in the measurement. This 1992 to 2007 comparison is more fully explained later in the text, but is represented graphically by Figure 1.LLRpt Fig 23

Dock Construction Guidelines and Regulations

As to dock construction, the Oregon State Marine Board provides guidelines for design of “Boarding Floats” (Docks) in their online guide associated with Boating Facility Grants. While these guidelines are a good platform for discussion, they do not regulate the design and construction of even public boat docks statewide let alone all private docks which dominate Devils Lake’s shoreline. Dock construction is widely variable as are uses. Private landowners may seek to provide a wide range of access for their sites including access for boats requiring little draft, (Paddle boats, kayaks, canoes, and Jet Skis) to those with higher draft requirements such as large powerboats and sailboats. The variability of the uses and owner preferences largely dictates the types of structures present. Additionally the time period for which a dock was built may further dictate the structure shape and size (e.g. compare popularity of fishing boats in the 1970’s and 80’s with Wake board boats of today). Nonetheless a cursory review of the state’s design  guidelines for new grant supported facilities suggests a minimum of 3’, (4’ preferred) of water depth for floats at the Design Low Water (DLW). Design Low Water, is the operational low water, which may or may not correspond with actual Ordinary Low Water (OLW).

Additional insight into boating needs is further expressed in the design guidelines for channel depths. For small outboard motorboats under 16’ (such as our own DLWID boat), 2’ is required for safe propeller clearance. For medium boats, 16’-26’ in length, the guidelines suggest 3’. It is notable that the entire boat dock survey was conducted using the District’s boat and thus the vast majority of properties on the lake (with few exceptions) were accessible by at least a smaller motorized craft (2’ propeller clearance). This is notable as Devils Lake itself has only an average depth of 8’ (Eilers 2005).

Further inquiry with Stuart Jantze E.I.T., a Boating Facilities Designer with the grant funded programs administered by Oregon State Marine Board, echoed a minimum 3’ depth for public facilities on Devils Lake based on the typical boats present (pers. comm. 2012-11-26). Mr. Jantze could not provide a state statute or otherwise providing maximum distances from the shoreline a facility could be built, but provided an ADA requirement that allows 80’ of structure to be built away from the shoreline to accommodate a ramp slope suitable for wheelchair access.

As to dock lengths, in speaking with Mike DeBlasi, Lands Specialist with Oregon Department of State Lands, the state may provide up to 25% of the width of a waterbody, not to exceed 500’ to build a structure suitable for water access (pers. comm. 2012-11-26). This interpretation has been in place since 1994 and will become part of the rules in January 2013 (See OAR 141-082-0260-(6) (g)). While in practice this largely applies to streams and rivers this limitation may also affect areas in coves or bays in which the distances are more limited. Additionally, in such case when an upland land owner’s preference right may overlap with the adjacent landowner’s dock, the maximum distance of 500’ may be reduced. However, as is the case now and into the expected rules to be adopted in January 2013, the Director may provide exceptions to the rules and the only limits would then be those potentially found in local ordinances detailed below.

Stuart Cowie of Lincoln County Planning and Development who administers the local planning on the lake in these matters relates that the County has jurisdiction on the lake except for a small area near the D River. County ordinances allow individual property owners to have a dock for the purpose of mooring a boat that extends into the lake 50’ from the Ordinary High Water (10.4’) or 25’ from the Ordinary Low Water (no value given). As a result the permit requests that do come in are invariable using the OHW mark. A conditional use can be obtained to extend beyond the 50’ should the upland property owner be able to show that they need additional depth to moor their boat. Aerial photography reveals that Devils Lake is dominated with boat docks no longer than 50’, but there are docks extending up to 100’. Adjacent property owner concerns however must be considered as must any issue with navigation of the lake itself. Cowie continued to state that the depth for safe moorage is dependent on the vessel itself (pers. comm. 2012-12-05). Therefore by example a sailboat with 5’ of draft would not be limited to what is commonly suggested as safe moorage for vessels of less draft. Notably then, only in practice is the idea of “safe moorage” applied as neither the Oregon State Marine board, Oregon Department of State Lands, nor Lincoln County Planning at the local level state what depth is “safe moorage”.

Existing Infrastructure

There are some 393 structures on Devils Lake. Based on an aerial photograph analysis the vast majority of dock structures were likely built pre-impoundment. In the sample provided in May 2012 of Johns Loop in Neotsu, 39 structures are visible in 1992 while only 2 more are shown in the 2007 aerial Figure 1). Further the structure themselves are typically very similar in size and capacity from the two periods. Thus fixed docks (non-floating) built pre-dam may likely be best suited for water depths which occur naturally in the summer period without impoundment. A lake wide survey of this same data comparison of 1992 to 2007 shows a similar, but less marked trend. As some of the aerials are poor from the earlier period, less confidence exists in this lake wide count. However of the 393 structures, 300 can confidently be said to have existed pre 1992, 63 likely built sometime post 1992, and 30 of total being to difficult to ascertain from the aerials.

Further classifications were made for Public vs. Private facilities. Public facilities on Devils Lake include fully improved boat-launchable sites at Regatta Grounds, Holmes Road Park, and East Devils Lake State Recreation Site. These sites and ramps are designed for water levels from ordinary low water through ordinary high water. Lesser improved launches include Sand Point and the State Park off of NE 1st street. While the graveled launch pads and lack of full time maintenance make them more suitable for smaller craft particularly kayaks and canoes, larger vessels are commonly seen using these sites as well.

Figure 1. Aerial photographs from 1992 and 2007 comparing dock structures for size and number.LLRpt Fig 24

Boat lifts were also characterized by this survey. In total 67 boat lifts were counted on the lake. These include more historic configurations and designs likely of the 1960’s-1980s to those with brand name more modern designs such as the Aqua Lift. Measurements were taken at the boat motor end of these structures. Of the 67 lifts, 9 (13%) would be in waters less than 3’ at 9.53, 18 lifts (27%) would be in waters less than 3’at 9.0’ and 37 (55%) when the lake was at 8.6’. We received one call from a concerned citizen regarding the accessibility of his Aqua-Lift boat lift under the water regime change in 2012. According to the manufacture of Aqua-Lift, this system is easily adjusted to various water depths down to 30” as the construction is like a bed frame (pers. Comm. 2012-12-06). He suggested that users may typically “scoop out” sediment that lies beneath the lift if greater depths are required, or reposition the lifts accordingly as they are free standing and as stated on their website are easily removed for winter storage. Based on there general configuration, water fluctuation of 3’ can be handled with greater fluctuations tolerated such as seen in estuarine systems with their XL models which are available in all classes of the lifts with the exception of the Mini-Aqua for Personal water crafts.

Sediment transport, wave action, and depth of water

A major factor in the sediment distribution is dictated by wave action. Given the unconsolidated nature of much of Devils Lake’s sediment (muck), it in particular is highly influenced by disruption and thus can be transported readily. Wave action from wind, boats and to a lesser extent current are the major forces causing disruption of the sediment particularly at the nearshore. Waves that come ashore will begin disrupting the sediment when the distance from the still water height is 1.25 times the height of the wave (Tetra Tech, 2012). Given the nature of waves from our most violent windstorms and wakes from the largest of vessels rarely exceed 3’, it is little surprise that most of the shoreline tapers to depth of no more than a few feet, the typical depth waves interact with the substrate. Muck in particular is unstable in these regions and the wave action tends to then mobilize the muck in favor or heavier sands and gravels which may remain. This phenomenon is viewable at many of the public access, particularly East Devils Lake State Park where in the small wading area near the fishing dock, the shallow, sandy shoreline gives way to murky, mucky waters only several feet offshore. What then can be deduced by this analysis is that if the lake is artificially held higher, then the muck would be more stable under the deeper area and would then be able to accumulate. This could reach the extent that the additional impoundment would ultimately have only a short term effect on water depth as mucky sediment moved inward to the shore coming into equilibration with the water depth and the incoming water energy’s capacity to disrupt the sediment.

Evidence to the truly unstableness of these unconsolidated sediments was seen through much of the lake. For example one dock which was home to a large boat had 4-5’ of depth near where it was moored while the adjacent dock which was seemingly unused had less than 1’. The sheer motor strength of the powerboat was apparently clearing the muck away, significantly deepening the channel approach as well as the docking area. As a result it would seem likely that in areas where loose mucky sediment dominates and even potentially in most sandy substrates, that the upland property owner and users of the dock could have the greatest impact as to what depth of water was available at the dock structure based on whether it was getting much use.

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